Previous changes

March 2024 — minor update. Fixed eruption added as an adverse effect of doxycycline as per the manufacturer's SPC.

August 2023 — minor update. Content in Wound Management sections restructured. No changes were made to recommendations. 

August 2023 — minor update. Typographical error corrected in the management of animal bites.

July 2023 — minor update. The manufacturer's SPC for metronidazole has been updated to note that QT prolongation has been reported (unknown frequency), particularly when metronidazole was administered with drugs with the potential for prolonging the QT interval.

May 2023 — minor update. Added potential adverse effects of co-amoxiclav to include Kounis syndrome (an allergic reaction which can result in myocardial infarction), aseptic meningitis, linear IgA disease (renal deposition of IgA), and drug-induced enterocolitis syndrome (all of unknown frequency). These adverse effects were noted in an update to the manufacturer’s summary of product characteristics.

March 2023 — minor update. A minor formatting change has been made to the section on wound care.

January 2023 — reviewed. A literature search was conducted in January 2023 to identify evidence-based guidelines, UK policy, systematic reviews, and key RCTs published since the last revision of the topic. Recommendations for assessment and management are largely based on the 2020 NICE guideline Human and animal bites: antimicrobial prescribing and the Public Health Wales guideline Health Protection Team Guidance for the Management of Human Bite Injuries in Wales (2019). As the topic had been updated to incorporate the 2020 NICE guidance since the last major review, no significant changes to recommendations have been made.

August 2021 — minor update. Adverse effects of co-trimoxazole updated in line with revised manufacturer's SPC relating to the rare problem of severe respiratory toxicity with the potential to progress to Adult Respiratory Distress Syndrome.

October 2020 — minor update. New advice from NICE Human and animal bites: antimicrobial prescribing guidance has been incorporated. These changes relate primarily to the advice on when to prescribe antibiotics for human and animal bites, the number of days advised for antibiotic prescriptions for treatment and for prophylaxis, and the indications for secondary care referral for people suffering bites. The choice of antibiotics has also been revised, clarithromycin has been removed and co-trimoxazole has been added as an alternative first-choice oral antibiotic for children under 12 years for penicillin allergy or if co-amoxiclav is unsuitable. This is an off-label use of co-trimoxazole. 

October 2018 — minor update. Adverse effects updated within prescribing information - metronidazole. 

February 2018 — minor update. New guidance from Public Health England regarding Rabies: administration of vaccine and immunoglobulin added to new evidence section.

February 2018 — revised. A literature search was conducted in December 2018 to identify evidence-based guidelines, UK policy, systematic reviews, and key RCTs published since the last revision of the topic. The topic now covers dog and cat bites and the scenario on pre-exposure rabies risk has been removed. There have been structural changes to streamline the scenarios. Antibiotic choices for prophylaxis and treatment of infected bite wounds have been simplified and antibiotic doses added to prescribing information. There have been changes to the recommendations on closing bite wounds in primary care.

March 2017 — minor update. New Public Health England guidelines on post-exposure treatment incorporated into the managing rabies section. 

July 2015 — minor update. The information on the concurrent use of clarithromycin or erythromycin with statins has been clarified.

February 2013 — minor update. The 2013 QIPP options for local implementation have been added to this topic.

October 2012 — minor update. The 2012 QIPP options for local implementation have been added to this topic.

January 2012 — revised. A literature search was conducted in October 2011 to identify evidence-based guidelines, UK policy, systematic reviews, and key RCTs published since the last revision of the topic. No changes to clinical recommendations have been made. 

July 2011 — minor update. More exact paracetamol dosing for children has been introduced by the Medicines and Healthcare products Regulatory Agency. Prescriptions have been updated to reflect the revised dosing. 

June 2011 — minor update. The 2010/2011 QIPP options for local implementation have been added to this topic. 

March 2011 — topic structure revised to ensure consistency across CKS topics — no changes to clinical recommendations have been made.

August 2009 — minor update. Advice from the National Institute for Health and Care Excellence guideline on when to suspect child maltreatment has been added to this topic. 

February 2009 — minor update. Clarithromycin added as an antibiotic option if a person is allergic to penicillin, in line with advice from the Health Protection Agency. Link updated to Health Protection Agency Clinical Rabies Service document. 

May 2008 — minor update to the text for animal bites, making it clearer that all cat bites require antibiotic prophylaxis. 

December 2007 — minor update to the text for animal bites. CKS now recommends that specialist advice should be sought for children under 12 years old who require antibiotic treatment and are allergic to penicillin, because they are unable to receive a tetracycline. 

August 2007 — minor update to text to clarify that, if tetanus vaccination is required, a combined tetanus vaccination should be used. Minor rewording of the Clinical Summaries on Assessing a bite, Managing a human bite, and Managing a cat and dog bite. 

April to July 2007 — converted from CKS guidance to CKS topic structure. The evidence base has been reviewed in detail, and recommendations are more clearly justified and transparently linked to the supporting evidence.

March 2004 — reviewed. Validated in May 2004 and issued in July 2004.

May 2001— reviewed. Validated in July 2001 and issued in October 2001.

New evidence

Evidence-based guidelines

No new evidence-based guidelines since 1 January 2023.

HTAs (Health Technology Assessments)

No new HTAs since 1 January 2023.

Economic appraisals

No new economic appraisals relevant to England since 1 January 2023.

Systematic reviews and meta-analyses

No new systematic reviews or meta-analyses published since 1 January 2023.

Primary evidence

No new primary evidence which reaches the CKS threshold for inclusion published since 1 January 2023.

New policies

No new national policies or guidelines since 1 January 2023.

New safety alerts

No new safety alerts since 1 January 2023.

Changes in product availability

No changes in product availability since 1 January 2023.

How should I assess someone with a human bite?

• Document how and when the bite occurred.
  • Who was bitten, and by whom.
  • Whether the skin was broken or blood was involved.
  • The nature of the bite (i.e. occlusal or clenched fist).
• Monitor vital signs if the bite is particularly traumatic, or sepsis is suspected.
• Examine the bite using gloves, bearing in mind that deep layers of tissue may move with positional changes after the bite injury, disguising the true depth of the wound. Document the following (record both positive and negative findings as there may be future litigation):
  • The location of the wound. Photographs or diagrams may be useful.
  • The size and depth of the injury.
    • An intercanine distance of less than 3 cm suggests a child bite; more than 3 cm suggests an adult bite.
  • The type of wound (for example laceration, puncture, abrasion, crush, haematoma, avulsion, or amputation).
  • The degree of crush injury, devitalized tissue, nerve or tendon damage, and involvement of muscle, bones, joints, or blood vessels.
    • Examine wounds overlying a joint through the full range of motion to detect retracted injuries and tendon rupture.
  • Neurovascular function in the area distal to the bite — check pulses and sensation.
  • The range of movement of any adjacent joints.
  • Any lymphadenopathy.
  • The presence of any foreign bodies (for example teeth) in the wound.
  • Any signs of infection (for example redness, swelling, induration, fluctuance, necrotic tissue, purulent discharge, pain, localized cellulitis, lymphangitis, lymphadenopathy, or fever).
  • Facial bites: perform an intraoral examination to exclude cheek lacerations with an intraoral communication.
• Determine whether the person is at increased risk of the wound becoming infected, due to:
  • The nature of the bite (deep, contaminated wounds; puncture or crush wounds; or significant tissue destruction).
  • Site of injury (for example hands, feet, face, or genitals; areas of poor perfusion or lymphatic return; or near a prosthetic joint implant). 
  • Wound penetrating bone, joints, tendons, or vascular structures.
  • Delayed presentation (more than 8 hours).
  • Associated medical conditions (for example diabetes mellitus, asplenia, immunocompromised status, chronic liver disease, or prosthetic heart valve or joint).
  • Their age (neonates, infants, and elderly people are at higher risk of infection).
• Although rare, suspect child maltreatment if there is a report or appearance of a human bite mark that is thought unlikely to have been caused by a young child. Also consider safeguarding issues if a vulnerable adult receives a bite injury.
  • Refer for further assessment in line with local policy.
• Assess the person's risk of tetanus and blood-borne virus infection.

How should I assess the risk of tetanus and blood-borne virus infection?

• To assess the risk of tetanus:
  • Enquire about tetanus immunization status. 
  • Determine whether the injury is considered to be a tetanus-prone wound; for example, there is:
    • A need for surgical intervention which is delayed for more than 6 hours.
    • A significant amount of devitalized tissue
    • A puncture wound (especially if in contact with soil or manure).
    • Contamination with material likely to contain tetanus spores, such as soil or manure.
    • A foreign body in the wound.
    • A compound fracture.
    • Systemic sepsis.
  • For more information see the UK Health Security Agency publications, Immunisation against infectious disease (the 'Green Book') and Tetanus: guidance for health professionals. 
• To assess the risk of acquiring a blood-borne viral infection (for example hepatitis B or C, or HIV):
  • Assess the status of the person who has been bitten (and the biter if possible):
    • Check their vaccination status for hepatitis B (and surface antibody response if applicable).
    • Ask if they are known to be HIV positive, hepatitis B surface antigen (HBsAg) positive, or hepatitis C positive.
    • For more information on groups of people at increased risk of these infections, see the CKS topics on Hepatitis B, Hepatitis C, and HIV infection and AIDS. 
    • Note that if the bite has not broken the skin there is no risk of blood-borne virus transmission. 
  • Offer to test for Hepatitis B, Hepatitis C, and HIV (see table 1). For more information on testing and interpretation of test results, see the CKS topics on Hepatitis B, Hepatitis C, and HIV infection and AIDS.  
    • If a child has received a bite, discuss their risk with a specialist (for example a consultant virologist) as it may be possible to avoid testing and the associated anxiety of venepuncture.
  • In most cases the status of the biter will not be known and it is often not practical to obtain a blood sample for testing, but if appropriate, and informed consent is given, the biter should also have their blood tested. Theoretically the biter is at higher risk given they will be exposed to the injured person's blood, whereas the person who has been bitten would usually be exposed to saliva only, unless the biter also has blood in their mouth.

Table 1. Blood tests following a bite injury

How should I manage a human bite wound?

• For initial wound management:
  • If possible remove any foreign bodies (for example teeth) from the wound.
  • Encourage the wound to bleed (if it has just occurred), unless it is already bleeding freely.
  • Irrigate thoroughly with warm, running water or normal saline. 
  • Consider the need for debridement (for example, if the wound is dirty or there is non-viable tissue). Refer to Accident and Emergency if this is required and the skills and resources are not available in primary care.
  • Advise analgesia (paracetamol or ibuprofen) for pain relief, if required.
  • Where body tissue has been torn off as a result of a bite, wrap any torn-off parts (for example, part of an ear) in clean tissue and store in a plastic bag surrounded by ice for transport to hospital.
  • Cover the wound with an appropriate clean dressing.
• Consider whether closure of the wound is appropriate.
  • Referral to Accident and Emergency for further assessment and management is usually indicated if wound closure is thought to be necessary. Note the types of bites for which referral is always recommended.
    • If the expertise and resources are available in primary care, seek specialist advice before attempting closure. Types of wounds that may be considered for closure include uncomplicated wounds with no risk factors for infection (for example, those presenting early which are not heavily contaminated, have been adequately irrigated and debrided, and do not involve underlying structures). 
  • Allow the following bite wounds to heal without formal closure:
    • Bite wounds over 24 hours old.
    • Infected bite wounds.
    • Deep puncture wounds.
    • Crush injuries.
    • Heavy contamination.
    • Uncertain adequacy of debridement.
    • Bites to the limbs, hands, and feet.
• Do not offer antibiotic prophylaxis to people with a human bite that has not broken the skin.
• Offer antibiotic prophylaxis to people with a human bite that has broken the skin and drawn blood.
• Consider antibiotic prophylaxis for people with a human bite that has broken the skin but not drawn blood if it:
  • Involves a high-risk area such as the hands, feet, face, genitals, skin overlying cartilaginous structures, or an area of poor circulation.
  • Is in a person at risk of a serious wound infection because of a comorbidity (such as diabetes, immunosuppression, asplenia, or decompensated liver disease).
• If antibiotic prophylaxis is indicated, prescribe co-amoxiclav for 3 days first line for children aged over one month and adults. If there is a penicillin allergy, or co-amoxiclav is unsuitable: 
  • For adults and young people aged 12 to 17 years, prescribe metronidazole plus doxycycline for 3 days.
  • For children aged under 12 years, prescribe co-trimoxazole for 3 days.
  • For more information on dosing, contraindications and cautions, adverse effects, and drug interactions, see Prescribing information.
• If the wound is infected:
  • Send pus or a deep wound swab for culture, before cleaning the wound. State on the form that the swab is from an infected human bite. 
  • Treat empirically with oral antibiotics if there are symptoms or signs of infection, including increased pain, inflammation, fever, discharge, or an unpleasant smell emanating from the wound. 
  • Admit anyone who has a severe infection or who is systemically unwell as intravenous antibiotics may be required.
• For treatment of an infected bite, prescribe co-amoxiclav for 5 days first line for children aged over one month and adults. If there is a penicillin allergy, or co-amoxiclav is unsuitable: 
  • For adults and young people aged 12 to 17 years, prescribe metronidazole plus doxycycline for 5 days.
  • For children aged under 12 years, prescribe co-trimoxazole for 5 days.
  • For more information on dosing, contraindications and cautions, adverse effects, and drug interactions, see Prescribing information.
• Give follow-up advice if the person has not been referred to hospital.
  • If the bite wound is not infected — advise the person to check for signs of infection and if these develop to attend urgently for review. Consider arranging a routine review within 24 to 48 hours.
  • If the wound is infected — review at 24 and 48 hours to ensure the infection is responding to treatment. Advise the person to attend urgently for review if the infection worsens or if they feel increasingly unwell.
  • For follow-up testing of people who are at risk of a blood-borne virus, see Assessment of tetanus and blood-borne virus risk.
• Reassess the bite if:
  • Symptoms or signs of infection develop or worsen rapidly or significantly at any time, or do not start to improve within 24 to 48 hours of starting treatment.
  • The person becomes systemically unwell.
  • The person has severe pain that is out of proportion to the infection.
• Be aware that people who have difficulty communicating may have nonverbal signs of pain, such as a change in behaviour.
• If a skin swab has been sent for microbiological testing, review the choice of antibiotic based on the swab results. If a change of antibiotic is needed, use a narrow-spectrum antibiotic if possible. 

How should I manage a person's risk of tetanus and blood-borne viruses?

• To manage a person's risk of tetanus:
  • Refer to updated information on the management of tetanus risk, depending on the person's immunization status and the risk status of the wound, in the chapter on tetanus in the UK Health Security Agency (UKHSA) publication Immunisation against infectious disease (the 'Green Book') and the Public Health England document Tetanus: guidance for health professionals. These guide health professionals in the management of tetanus-prone wounds and advise on the need for vaccine booster and/or human tetanus immunoglobulin, which may be required depending on age, vaccination status, and the level of risk of tetanus.
• To manage a person's risk of blood-borne viruses:
  • Seek immediate advice from a consultant in infectious diseases, a virologist, or the local Health Protection Team for anyone considered to be at risk of HIV or hepatitis B from a bite wound. Consider all people to be at risk unless the current status of the biter is known (rare).
    • For more information on Hepatitis B prophylaxis for reported exposure incidents, see chapter 18 of Immunisation against infectious disease (the 'Green Book'), published by the UK Health Security Agency (UKHSA).

When should I refer someone with a human bite?

• Refer to secondary care (with urgency depending on clinical judgement):
  • Severe bite injuries with heavy bleeding causing haemodynamic instability.
  • Penetrating wounds involving arteries, joints, nerves, muscles, tendons, bones, or the central nervous system. Note: penetrating bites to the hands (particularly bites to a clenched fist), feet, or head are at particular risk of infection and serious complications. 
  • Facial wounds (excluding very minor wounds) and bites to the eye or orbit. 
  • Bites where there is a possibility of a foreign body (for example a tooth) in the wound. 
  • Devitalized wounds where debridement is required, or wounds that might benefit from closure. 
  • Injuries requiring reconstructive surgery.
  • People with abscesses, severe cellulitis, lymphangitis, osteomyelitis, septic arthritis, necrotising fasciitis or with infected bite wounds that are not responding to treatment, or who are systemically unwell with possible sepsis. 
  • People with an increased risk of infection; for example, diabetes mellitus, asplenia, immunocompromised status, chronic liver disease, or prosthetic heart valve or joint. 
  • Bites to poorly vascularized areas such as ear cartilage/nose cartilage.
  • People who cannot take oral antibiotics (in which case, explore with the specialist whether locally available options for parenteral antibiotics at home or in the community, rather than in hospital, are appropriate).
  • People who have developed signs or symptoms of significant infection whilst taking antibiotics or are on prophylactic antibiotics.
• If bite wounds suggest possible child protection issues or safeguarding issues for a vulnerable adult, refer for further assessment in line with local policy.
• If the person is at risk of tetanus and assessment suggests they may require tetanus immunoglobulin, seek specialist advice. 
• If there is a possibility that the person has been exposed to a blood-borne virus such as hepatitis B or HIV, seek immediate advice from a consultant in infectious diseases, a virologist, or the local Health Protection Team. For more information see Managing risk of tetanus and blood-borne viruses.  

How should I assess someone with a dog or cat bite?

• Document how and when the bite occurred.
  • The type of animal (domesticated or wild) and its state of health or any unusual symptoms.
  • Whether the attack was provoked.
  • Mechanism of injury.
• Monitor vital signs if the bite is particularly traumatic, or sepsis is suspected.
• Examine the bite using gloves, bearing in mind that deep layers of tissue may move with positional changes after the bite injury, disguising the true depth of the wound. Document the following (record both positive and negative findings as there may be future litigation):
  • The location of the wound. Photographs or diagrams may be useful.
  • The size, extent, and depth of the injury.
  • The type of wound (for example laceration, puncture, abrasion, crush, haematoma, avulsion, or amputation).
  • The degree of crush injury, devitalized tissue, nerve or tendon damage, and involvement of muscle, bones, joints, or blood vessels.
    • Examine wounds overlying a joint through the full range of motion to detect retracted injuries and tendon rupture.
  • Neurovascular function in the area distal to the bite — check pulses and sensation.
  • The range and movement of any adjacent joints.
  • Any lymphadenopathy.
  • The presence of any foreign bodies (for example teeth) in the wound.
  • Any signs of infection (for example redness, swelling, induration, necrotic tissue, purulent discharge, pain, localized cellulitis, lymphangitis, lymphadenopathy, or fever).
  • Facial bites: perform an intraoral examination to exclude cheek lacerations with an intraoral communication. 
• Determine whether the person is at increased risk of the wound becoming infected, due to:
  • The type of animal — cat bites increase the risk of infection.
  • The nature of the bite (deep, contaminated wounds; puncture or crush wounds; or significant tissue destruction).
  • Site of injury (for example extremities such as hands, feet, face, or genitals; areas of poor perfusion or lymphatic return; or near a prosthetic joint implant).  
  • Wound penetrating bone, joints, tendons, or vascular structures.
  • Delayed presentation (more than 8 hours).
  • Associated medical conditions (for example diabetes mellitus, asplenia, immunocompromised status, chronic liver disease, or a prosthetic heart valve or joint).
  • Their age (neonates, infants, and elderly people are at higher risk of infection).
• Although rare, consider the possibility of child neglect if there is a report or appearance of an animal bite on a child who has been inadequately supervised. Refer for further assessment in line with local policy.
• Assess the person's risk of tetanus and rabies infection.

How should I assess the risk of tetanus and rabies?

• To assess the risk of tetanus:
  • Enquire about tetanus immunization status.
  • Determine whether the injury is considered to be a tetanus-prone wound; for example, there is:
    • A delay in surgical intervention for more than 6 hours.
    • Contamination with material likely to contain C. tetani spores, such as soil or manure.
    • A significant amount of devitalised tissue.
    • A puncture wound (especially if in contact with soil or manure).
    • A foreign body in the wound.
    • A compound fracture.
    • Systemic sepsis.
  • For more information see the UK Health Security Agency (UKHSA) publications, Immunisation against infectious disease (the 'Green Book') and Tetanus: guidance for health professionals.
• To assess the risk of rabies, enquire about the:
  • Country in which the person was bitten and the origin of the animal. 
    • The UK is considered to be a 'no risk' country, with no indigenous rabies in terrestrial animals. However, note that exposure to bats and their secretions is considered a potential rabies risk anywhere in the world. Certain groups of people in the UK are considered to be at increased risk of rabies (for example laboratory workers working with the rabies virus or people handling bats or imported animals). 
    • If the person was bitten abroad, the UK Health Security Agency's guidance on Rabies risks by country (for terrestrial animals) categorizes countries as no risk, low risk, or high risk. 
  • Site and severity of the wound — bites with broken skin, contamination of mucous membranes or skin lesions with an animal's saliva or body fluid, and proximal (head and neck) bites are considered to be high-risk.
  • Circumstances of the bite — unprovoked bites are considered higher risk.
  • Species of animal and its health status and behaviour in the days and weeks after the biting incident — abnormal behaviour increases the risk of infection.
  • Immune status of the person bitten based on history of rabies vaccination.
• A risk assessment should be performed on anyone who is at risk of rabies exposure using the UKHSA Rabies post exposure risk assessment form and calendar. In England, the risk assessment should be encrypted and emailed securely to the Rabies and Immunoglobulin Service. In addition to the above, the further information will be needed to complete the risk assessment: name, date of birth, age, address, NHS number, date of exposure, history of immunosuppression, and allergies.
• For more information on rabies risk assessment, see the UKHSA Collection on Rabies: risk assessment, post-exposure treatment, management (available at www.gov.uk) or seek specialist advice from:
  • England — Local health protection team or the UK Health Security Agency (UKHSA) Rabies and Immunoglobulin Service (tel. 0330 128 1020 Monday to Friday 8.30 am to 5pm), or out of hours UKHSA Colindale (tel. 020 8200 4400). 
  • Wales —  Public Health Wales health protection team (tel. 0300 003 0032) or duty virologist, University Hospital of Wales, Cardiff (029 20 747 747). 
  • Scotland — Local infectious diseases consultant on-call (contact details listed in chapter 27 on rabies in the green book).
  • Northern Ireland — The regional virology service (028 9024 0503) or the Public Health Agency Duty Room (030 0555 0119).

How should I manage a cat or dog bite wound?

• For initial wound management:
  • If possible remove any foreign bodies (for example, teeth) from the wound.
  • Encourage the wound to bleed (if it has just occurred), unless it is already bleeding freely.
  • Irrigate thoroughly with warm, running water or normal saline. It is usually not possible to irrigate small puncture wounds.
  • Consider the need for debridement (for example, if the wound is dirty or there is non-viable tissue) and refer to Accident and Emergency if this is required and the skills and resources are not available in primary care.
  • Advise analgesia (paracetamol or ibuprofen) for pain relief, if required.
  • Where body tissue has been torn off as a result of a bite, wrap any torn-off parts (for example, part of an ear) in clean tissue and store in a plastic bag surrounded by ice for transport to hospital.
  • Cover the wound with an appropriate clean dressing. 
• Consider whether closure of the wound is appropriate:
  • Referral to Accident and Emergency for further assessment and management is usually indicated if wound closure is thought to be necessary. Note the types of bites for which specialist referral is always recommended.
    • If the expertise and resources are available in primary care, seek specialist advice before attempting closure. Types of wounds that may be considered for closure include uncomplicated wounds with no risk factors for infection (for example, those presenting early which are not heavily contaminated, have been adequately irrigated and debrided, and do not involve underlying structures).
  • Allow the following bite wounds to heal without formal closure:
    • Bite wounds over 24 hours old.
    • Infected bite wounds.
    • Deep puncture wounds (for example, cat bites).
    • Crush injuries.
    • Heavy contamination.
    • Uncertain adequacy of debridement.
    • Bites to the limbs, hands, and feet.
• For people with cat bites:
  • Do not offer antibiotic prophylaxis to people with a cat bite that has not broken the skin. 
  • Offer antibiotic prophylaxis if the cat bite has broken the skin and drawn blood. 
  • Consider antibiotic prophylaxis for people with a cat bite that has broken the skin but not drawn blood if the wound could be deep. 
• For people with bites from a dog or other traditional pet (excluding cats):
  • Do not offer antibiotic prophylaxis for a bite that: 
    • Has not broken the skin.
    • Has broken the skin, but has not drawn blood.
  • Offer antibiotic prophylaxis if the bite has broken the skin and drawn blood if it: 
    • Has penetrated bone, joint, tendon, or vascular structures.
    • Is deep, is a puncture or crush wound, or has caused significant tissue damage.
    • Is visibly contaminated (for example, if there is dirt or a tooth in the wound).
  • Consider antibiotic prophylaxis if the bite has broken the skin and drawn blood if it:  
    • Involves a high-risk area such as the hands, feet, face, genitals, skin overlying cartilaginous structures or near prosthetic joints, or an area of poor circulation. 
    • Is in a person at risk of serious wound infection or systemic infection because of comorbidity (for example, diabetes mellitus, asplenia, immunosuppression, decompensated liver disease), or they have a prosthetic heart valve, or if they are at the extremes of age. 
• If antibiotic prophylaxis is indicated, prescribe co-amoxiclav for 3 days first line for children aged over one month and adults. If there is a penicillin allergy, or co-amoxiclav is unsuitable: 
  • For adults and young people aged 12 to 17 years, prescribe metronidazole plus doxycycline for 3 days.
  • For children aged under 12 years, prescribe co-trimoxazole for 3 days.
  • For more information on dosing, contraindications and cautions, adverse effects, and drug interactions, see Prescribing information.
  • Seek specialist advice for the most appropriate antibiotic for bites from other animals (for example, pigs). 
• If the wound is infected:
  • Send a pus or deep wound swab for culture, before cleaning the wound. State on the form that the swab is from an infected animal bite.
  • Treat empirically with oral antibiotics if there are symptoms or signs of infection, including increased pain, inflammation, fever, discharge, or an unpleasant smell emanating from the wound.
  • Admit anyone who has a severe infection or who is systemically unwell as intravenous antibiotics may be required.
• For treatment of an infected bite, prescribe co-amoxiclav for 5 days first line for children aged over one month and adults. If there is a penicillin allergy, or co-amoxiclav is unsuitable: 
  • For adults and young people aged 12 to 17 years, prescribe metronidazole plus doxycycline for 5 days.
  • For children aged under 12 years, prescribe co-trimoxazole for 5 days.
  • For more information on dosing, contraindications and cautions, adverse effects, and drug interactions, see Prescribing information.
• Give follow-up advice if the person has not been referred to hospital.
  • If the bite wound is not infected — advise the person to check for signs of infection and if these develop to attend urgently for review. Consider arranging a routine review within 24 to 48 hours.
  • If the wound is infected — review at 24 and 48 hours to ensure the infection is responding to treatment. Advise the person to attend urgently for review if the infection worsens or if they feel increasingly unwell.
  • Follow-up for people who require post-exposure prophylaxis for rabies should be as advised by a specialist. For more information, see Managing risk of tetanus and rabies.
• Reassess the animal bite if:
  • Symptoms or signs of infection develop or worsen rapidly or significantly at any time, or do not start to improve within 24 to 48 hours of starting treatment.
  • The person becomes systemically unwell.
  • The person has severe pain that is out of proportion to the infection.
• Be aware that people who have difficulty communicating may have non-verbal signs of pain, such as a change in behaviour.
• If a skin swab has been sent for microbiological testing, review the choice of antibiotic based on the swab results. If a change of antibiotic is needed, use a narrow-spectrum antibiotic if possible. 

How should I manage a person's tetanus and rabies risk?

• To manage a person's risk of tetanus:
  • Refer to updated information on the management of tetanus risk, depending on the person's immunization status and the risk status of the wound, in the chapter on tetanus in the UK Health Security Agency (UKHSA) publication Immunisation against infectious disease (the 'Green Book'), and document Tetanus: guidance for health professionals. These guide health professionals in the management of tetanus-prone wounds and advise on the need for vaccine booster and/or human tetanus immunoglobulin, which may be required depending on age, vaccination status, and level of risk of tetanus.
• To manage a person's risk of rabies: 
  • The need for treatment will be determined and organized by a specialist based on the person's rabies risk assessment. See the section on Assessment of tetanus and rabies risk for contact details for the appropriate specialist in England, Northern Ireland, Scotland, and Wales. 
  • Treatment recommendations are grouped into the following categories:
    • No risk, therefore no treatment.
    • Vaccine and human rabies immunoglobulin (HRIG).
    • Vaccine only.
    • Vaccine, HRIG, and blood test with the last dose of vaccine.
    • Observation of animal (domestic cats and dogs only).
  • If treatment is required but has not been started, post-exposure treatment should be commenced as soon as possible, ideally within 24 hours of contact. Initiating post-exposure treatment is not considered a medical emergency, and rabies vaccine/human rabies immunoglobulin (HRIG) can usually be sent out to be given the next day in most cases. However, for high-risk exposures, such as severe and multiple bites to the head and neck bites or from a confirmed rabid animal, treatment should ideally be started within 12 hours of reporting. NHS Trusts in England should have locally available rabies vaccine so that prompt treatment can be initiated.
  • The mainstay of post-exposure treatment is the rabies vaccine given by intramuscular injection at 0, 3, 7, and 21 days. HRIG may provide short-term immunity in the first week following the initiation of treatment.
  • It is important to note that vaccination and human rabies immunoglobulin should never be given at the same anatomical site. Vaccine doses are given in alternate arms.

When should I refer someone with a dog or cat bite?

• Refer to secondary care (with urgency depending on clinical judgement):
  • Severe bite injuries with heavy bleeding causing haemodynamic instability.
  • Penetrating wounds involving arteries, joints, nerves, muscles, tendons, bones, or the central nervous system. Note: penetrating bites to the hands, feet, or head are at particular risk of infection and serious complications. 
  • Children with scalp wounds and potential penetrating wounds to the skull.
  • Facial wounds (excluding very minor wounds) and bites to the eye or orbit.
  • Serious hand bites.
  • Bites where there is a possibility of a foreign body (for example a tooth) in the wound.
  • Devitalized wounds where debridement is required or wounds that might benefit from closure.
  • Bites that might need reconstructive surgery.
  • People with abscesses, lymphangitis, severe cellulitis, osteomyelitis, septic arthritis, necrotising fasciitis, infected bite wounds that are not responding to treatment, or who are systemically unwell.
  • People with an increased risk of infection — for example, diabetes mellitus, asplenia, immunocompromised status, chronic liver disease, or a prosthetic heart valve or joint.
  • Bites to poorly vascularized areas such as ear cartilage/nose cartilage.
  • People who cannot take oral antibiotics (in which case, explore with the specialist whether locally available options for parenteral antibiotics at home or in the community, rather than in hospital, are appropriate)
  • People who have developed signs or symptoms of significant infection whilst taking antibiotics or are on prophylactic antibiotics.
• If an animal has bitten a child, consider the possibility of poor parenting and supervision. Follow local policies for referral of children considered at risk.
• If the person is at risk of tetanus and assessment suggests they may require tetanus immunoglobulin, seek specialist advice. 
• If there is a possibility that the person has been exposed to rabies, seek immediate advice from:
  • England — Local health protection team or the UK Health Security Agency (UKHSA) service Rabies and Immunoglobulin Service (tel. 0330 128 1020 Monday to Friday 8.30 am to 5pm), or out of hours UKHSA Colindale (tel. 020 8200 4400). 
  • Wales —  Public Health Wales health protection team (tel. 0300 003 0032) or duty virologist, University Hospital of Wales, Cardiff (029 20 747 747). 
  • Scotland — Local infectious diseases consultant on-call (contact details listed in chapter 27 on rabies in the green book).
  • Northern Ireland — The regional virology service (028 9024 0503) or the Public Health Agency Duty Room (030 0555 0119).

What dosage of co-trimoxazole should I prescribe?

• For treatment of an infected bite wound as an alternative first-choice oral antibiotic for children under 12 years where co-amoxiclav cannot be used, the dosage of oral co-trimoxazole is:
  • 6 weeks to 5 months: 120 mg or 24 mg/kg twice a day for 5 days.
  • 6 months to 5 years: 240 mg or 24 mg/kg twice a day for 5 days.
  • 6 years to 11 years: 480 mg or 24 mg/kg twice a day for 5 days.
• For prophylaxis of a bite wound, the dosage is as described above but prescribed for 3 days. 
• Note this is considered an off-label or unlicensed use, but is recommended in the National Institute for Health and Care Excellence (NICE) guideline Human and animal bites: antimicrobial prescribing.

[NICE, 2020; BNF, 2022]

What are the contraindications and cautions when prescribing co-trimoxazole?

• Do not prescribe co-trimoxazole in children:
  • With acute porphyrias.
  • With hypersensitivity to sulphonamides, trimethoprim, or co-trimoxazole.
  • With severe parenchymal hepatic disease.
  • In the first 6 weeks of life.
  • With severe renal insufficiency.
  • With previous drug-induced thrombocytopaenia from use of trimethoprim and/or sulphonamides. 
• Prescribe co-trimoxazole with caution in children with:
  • Asthma or severe atopy.
  • Blood disorders (unless under specialist supervision).
  • G6PD deficiency (risk of haemolytic anaemia).
  • A predisposition to folate deficiency.
  • A predisposition to hyperkalaemia.

     [ABPI, 2021a; BNF for children, 2022]

What are the adverse effects of co-trimoxazole?

• Common adverse effects of co-trimoxazole include diarrhoea, electrolyte imbalance, fungal overgrowth, headache, nausea, and skin reactions.
• Less commonly it can cause vomiting. 
• Rare adverse effects include thrombocytopenia and other blood disorders including leucopenia, megaloblastic anaemia, and eosinophilia. It can also cause a severe rash (including Stevens–Johnson syndrome or toxic epidermal necrolysis) and severe respiratory toxicity including potential progression to Adult Respiratory Distress Syndrome. It should be discontinued immediately if these severe adverse effects are caused. 

[ABPI, 2021a; BNF for children, 2022]

What drug interactions are associated with co-trimoxazole?

• ACE inhibitors and angiotensin receptor blockers — caution should be exercised in patients taking any other drugs that can cause hyperkalaemia. Concomitant use of co-trimoxazole may result in hyperkalaemia.
• Azathioprine — there are conflicting clinical reports of interactions between azathioprine and trimethoprim-sulfamethoxazole, resulting in serious haematological abnormalities.
• Cyclosporin — reversible deterioration in renal function has been observed in patients treated with co-trimoxazole and cyclosporin following renal transplantation.
• Folinic acid — folinic acid supplementation has been shown to interfere with the antimicrobial efficacy of trimethoprim-sulfamethoxazole.
• Lamivudine — concomitant co-trimoxazole causes an increase in lamivudine exposure.
• Methotrexate — co-trimoxazole may increase the free plasma levels of methotrexate. If co-trimoxazole is considered appropriate therapy a folate supplement should be considered.
• Phenytoin — co-trimoxazole prolongs the half-life of phenytoin and if co-administered could result in an excessive phenytoin effect. Close monitoring of the patient's condition and serum phenytoin levels are advisable.
• Pyrimethamine — occasional reports suggest that patients receiving pyrimethamine at doses in excess of 25 mg weekly may develop megaloblastic anaemia should co-trimoxazole be prescribed concurrently.
• Repaglinide — trimethoprim may increase the exposure of repaglinide which may result in hypoglycaemia.
• Spironolactone — caution should be exercised in patients taking any other drugs that can cause hyperkalaemia. Concomitant use of co-trimoxazole may result in hyperkalaemia.
• Sulfonylureas — interaction with co-trimoxazole is uncommon, but potentiation has been reported.
• Warfarin — co-trimoxazole has been shown to potentiate the anticoagulant activity of warfarin. Careful control of the anticoagulant therapy during treatment with co-trimoxazole is advisable.
• Zidovudine — in some situations, concomitant treatment with zidovudine may increase the risk of haematological adverse reactions to co-trimoxazole. If concomitant treatment is necessary, consideration should be given to monitoring of haematological parameters.

[ABPI, 2021a]

What dosage of co-amoxiclav should I prescribe?

• For treatment of an infected bite wound, the dosage of oral co-amoxiclav is:
  • Adult: 250/125 mg or 500/125 mg 3 times a day for 5 days
  • Child 1–11 months: 0.25 mL/kg of 125/31 suspension three times a day for 5 days. 
  • Child 1–5 years: 0.25 mL/kg or 5 ml of 125/31 suspension three times a day, for 5 days. 
  • Child 6–11 years: 0.15 mL/kg or 5 ml of 250/62 suspension three times a day, for 5 days. 
  • Child 12–17 years: 250/125 mg or 500/125 mg 3 times a day for 5 days. 
• For prophylaxis of a bite the dosage is as described above but prescribed for 3 days in both adults and children. 
• Co-amoxiclav 400/57 suspension may be considered to allow for twice-daily dosing.

[NICE, 2020; ABPI, 2021b; BNF, 2022; BNF for children, 2022] 

What are the contraindications and cautions when prescribing co-amoxiclav?

• Do not prescribe co-amoxiclav in people with:
  • A true penicillin allergy — allergic reactions to penicillins occur in 1–10% of exposed individuals; anaphylactic reactions occur in fewer than 0.05% of treated patients.
    • Note: Gastrointestinal adverse effects alone (for example nausea, vomiting, or diarrhoea) do not constitute an allergy to penicillin. See the CKS topic on Angio-oedema and anaphylaxis for more information.
  • A history of co-amoxiclav- or penicillin-associated jaundice or hepatic dysfunction.
• Prescribe co-amoxiclav with caution in people with:
  • A hypersensitivity to cephalosporins — there is some evidence of partial cross-allergenicity. 
  • Hepatic impairment – monitor closely.
  • Chronic kidney disease (CKD) — reduce the dose if the estimated glomerular filtration rate (eGFR) is 30 mL/minute/1.73 m² or less.
  • Acute lymphocytic leukaemia, chronic lymphocytic leukaemia, cytomegalovirus infection, glandular fever — increased risk of erythematous rashes.

 [ABPI, 2021b; BNF, 2022; BNF for children, 2022]

What are the adverse effects of co-amoxiclav?

• Gastrointestinal — diarrhoea (very common), nausea and vomiting (common), drug-induced enterocolitis syndrome (unknown frequency).
  • Very rarely: antibiotic-associated colitis.
• Nervous system — headache, dizziness (uncommon), aseptic meningitis (unknown frequency).
• Skin — skin rash, urticaria, pruritus (uncommon), drug reaction with eosinophilia and systemic symptoms (DRESS) (unknown frequency).
  • Very rarely: erythema multiforme, Stevens–Johnson syndrome, toxic epidermal necrolysis, bullous and exfoliative dermatitis, acute generalized exanthematous pustulosis.
• Other rare, or very rare adverse effects include:
  • Hepatitis, cholestatic jaundice.
  • Hyperactivity, convulsions.
  • Hypersensitivity reactions (serious and occasionally fatal).  
  • Interstitial nephritis.
  • Linear IgA disease (renal deposition of IgA).  
  • Leucopenia, thrombocytopenia, haemolytic anaemia.
  • Kounis syndrome (an allergic reaction which can cause myocardial infarction). 
• Symmetrical Drug-related Intertriginous and Flexural Exanthema (SDRIFE) are adverse effects of unknown frequency.

[BNF, 2023; ABPI, 2023; EMC, 2024a]

What drug interactions are associated with co-amoxiclav?

• Allopurinol — concomitant use of allopurinol and amoxicillin may increase the incidence of skin rashes.
• Methotrexate — co-amoxiclav may reduce methotrexate clearance, causing an increased risk of toxicity.
  • Monitor methotrexate levels more closely. One recommendation is to carry out twice weekly platelet and white cell counts for 2 weeks initially, with the measurement of methotrexate levels if toxicity is suspected.
• Mycophenolate mofitil — reduction in the level of active metabolite may occur when given with co-amoxiclav.
• Oral anticoagulants (warfarin, phenindione, acenocoumarol) — prolongation of prothrombin time has been reported in people taking penicillins and warfarin concurrently.
  • Monitor the prothrombin time or international normalized ratio (INR) more closely with the addition or withdrawal of a penicillin. Adjustment of the anticoagulant dose may be necessary. 
• Oral hormonal contraception — additional contraceptive precautions are not required during or after courses of co-amoxiclav.
  • However, women should be advised about the importance of correct contraceptive practice if they experience vomiting or diarrhoea. For further information, see the sections on vomiting or diarrhoea in the CKS topics on Contraception - combined hormonal methods and Contraception - progestogen-only methods.
• Probenecid — concomitant administration may result in increased levels of amoxicillin, but not clavulanic acid.

[ABPI, 2021b; BNF, 2022; CoSRH, 2022]

What dosage of doxycycline should I prescribe?

• For treatment of an infected bite wound, the dosage of oral doxycycline is:
  • Adults and young people aged 12–17 years: 200 mg on the first day and then 100 mg or 200 mg daily for a further 4 days (in addition to metronidazole 400 mg three times a day). [NICE, 2020].
    • Child: doxycycline is contraindicated in children less than 12 years of age because of the risk of dental staining and hypoplasia [BNF for children, 2022].
• For prophylaxis the dosage is as described above and prescribed for a total of 3 days [NICE, 2020].

What are the contraindications and cautions when prescribing doxycycline?

• Do not prescribe doxycycline in:
  • Women who are pregnant or breastfeeding, and children younger than 12 years of age.
    • Tetracyclines are deposited in growing bone and teeth which can result in discolouration of teeth and occasionally dental hypoplasia.
• Prescribe doxycycline with caution in people with:
  • Hepatic impairment and those receiving potentially hepatotoxic drugs.
  • Myasthenia gravis — tetracyclines may increase muscle weakness in people with myasthenia gravis.
  • Systemic lupus erythematosus (SLE) — tetracyclines may exacerbate SLE symptoms.
  • Renal impairment — avoid excessive doses.
  • Alcohol dependence - alcohol may decrease the half-life of doxycycline.
• Advise that the capsules should be swallowed with plenty of water in either the sitting or standing position and well before going to bed at night to lower the risk of oesophageal irritation and ulceration. 

[ABPI, 2021c; BNF, 2022]

What are the adverse effects of doxycycline?

• Blood disorders — haemolytic anaemia, thrombocytopenia, neutropenia, eosinophilia (rare).
• Gastrointestinal — nausea, vomiting, diarrhoea (common), dyspepsia (uncommon). Abdominal discomfort, tooth discolouration, and enamel hypoplasia in children (frequency unknown).
  • Rarely: dysphagia, oesophagitis, oesophageal irritation, pseudomembranous colitis. For more information, see the CKS topic on Diarrhoea - antibiotic associated. (Advice to swallow the capsules with plenty of water, in an upright position, and well before going to bed helps to reduce the frequency of oesophagitis and oesophageal ulceration.)
• Immune system disorders – hypersensitivity common (including anaphylaxis, angioedema, exacerbation of systemic lupus erythematosus, Henoch-Schonlein purpura). Rarely drug reaction with eosinophilia and systemic symptoms (DRESS).
• Hepatic disorders – hepatotoxicity, hepatitis, jaundice, hepatic failure (frequency unknown).
• Renal disorders — blood urea increased.
• Skin — photosensitivity, rash (common).
  • Rarely: toxic epidermal necrolysis, Stevens–Johnson syndrome, erythema multiforme, exfoliative dermatitis, and fixed eruption.
• Other rare adverse effects include:
  
  • Arthralgia, myalgia.
  • Flushing.
  • Severe headache and/or visual disturbances — may be an early symptom of benign intracranial hypertension, a rare but serious adverse effect. Headache is a relatively common side effect.
  • Tinnitus.

 [BNF, 2022; EMC, 2024b]

What drug interactions are associated with doxycycline?

• Antacids (containing aluminium, bismuth, calcium, or magnesium) and other medications containing iron or zinc — these reduce the absorption of tetracyclines if taken concurrently.
  • Avoid taking antacids and other medications containing iron or zinc, 2 hours before or after taking tetracyclines.
• CYP3A enzyme inducers (phenobarbital, carbamazepine, or phenytoin) — these may reduce the serum half-life of doxycycline and decrease the concentration of doxycycline. Monitor and adjust the dose if necessary.
• Insulin — the blood-glucose lowering effect may be increased if taken with doxycycline. Monitor blood-glucose levels.
• Iron — Oral iron may decrease absorption of oral doxycycline, so doxycycline should be taken 2 to 3 hours after iron.
• Lithium — levels may be increased by doxycycline. Consider increasing the frequency of lithium monitoring.
• Oral hormonal contraception — additional contraceptive precautions are not required during or after courses of doxycycline.
  • However, women should be advised about the importance of correct contraceptive practice if they experience vomiting or diarrhoea. For further information, see the sections on vomiting or diarrhoea in the CKS topics on Contraception - combined hormonal methods and Contraception - progestogen-only methods.
• Retinoids — there is a possible increased risk of benign intracranial pressure if tetracyclines are used concurrently with retinoids (such as isotretinoin).
  • Avoid the concurrent use of tetracyclines and retinoids.
• Rifampicin — doxycycline levels may be reduced, which may lead to treatment failure. Monitor the effects and increase doxycycline dose if necessary.
• Warfarin — the concurrent use of warfarin and other anticoagulants with tetracyclines may increase the anticoagulant effect. 
  • Consider monitoring the person's international normalized ratio (INR) regularly and within 3 days of starting the tetracycline. Adjust the warfarin dose accordingly.
  • Other anticoagulants: Acenocoumarol, phenindione  — the manufacturer recommends monitoring INR.

[ABPI, 2021c; BNF, 2022; CoSRH, 2022]

What dosage of metronidazole should I prescribe?

• For treatment of an infected bite wound, metronidazole is recommended as an alternative first-choice antibiotic for those unable to take co-amoxiclav. It is co-prescribed with doxycycline. For adults and young people aged 12 to 17 years, the dosage of oral metronidazole is 400 mg 3 times a day for 5 days.
• For prophylaxis of a bite in the same age range the dose is the same, but is prescribed for 3 days. 

[NICE, 2020]

What are the contraindications and cautions when prescribing metronidazole?

• Do not prescribe metronidazole in people with:
  • Known metronidazole hypersensitivity.
• Prescribe metronidazole with caution in people with:
  • Cockayne syndrome — cases of severe hepatotoxicity/acute hepatic failure, including cases with a fatal outcome with very rapid onset after treatment initiation in patients with Cockayne syndrome have been reported with products containing metronidazole for systemic use (oral and suppositories). Only prescribe after careful benefit-risk assessment and only if no alternative treatment is available. Liver function tests must be performed just prior to the start of therapy, throughout, and at the end of treatment until liver function is within normal ranges, or until the baseline values are reached.
  • Active or chronic severe peripheral and central nervous system disease, as there is a risk of neurological aggravation.
  • Severe liver disease or hepatic encephalopathy — prescribe one-third of the daily dosage once daily.

[ABPI, 2021d; BNF, 2022]

What are the adverse effects of metronidazole?

• Blood disorders — agranulocytosis, neutropenia, thrombocytopenia, pancytopenia (very rare).
• Eye — transient diplopia, myopia (very rare).
• Gastrointestinal — nausea, vomiting, anorexia, epigastric pain, taste disturbances, furred tongue, oral mucositis (unknown frequency). 
• Nervous system — drowsiness, dizziness, convulsions, headaches, encephalopathy (very rare)
• Psychiatric — confusion, hallucinations (very rare).
• Skin — rash, pruritus, flushing, erythema multiforme, Stevens–Johnson syndrome or toxic epidermal necrolysis, fixed drug eruption (very rare).
• Other rare, or very rare adverse effects include:
  • Anaphylaxis.
  • Darkening of urine.
  • Hearing impairment, tinnitus.
  • Liver enzyme increases, jaundice, pancreatitis.
  • Myalgia, arthralgia.
  • Severe bullous skin reactions such as Stevens-Johnson–syndrome, toxic epidermal necrolysis (TEN), or acute generalized exanthematous pustulosis (AGEP) have been reported. If symptoms/signs are present, treatment must be immediately discontinued.

[ABPI, 2021d; BNF, 2022]

What drug interactions are associated with metronidazole?

• Alcohol — some people taking metronidazole experience a disulfiram-like reaction with alcohol.
  • Warn the person that they might experience this reaction if they drink alcohol whilst on metronidazole and for at least 48 hours afterwards. 
• Busulfan — plasma levels of busulfan may be increased leading to toxicity. Avoid high doses of busulfan. If conventional doses of busulfan are given, monitor blood count weekly.
• Ciclosporin — levels of ciclosporin may be increased. If co-administration of metronidazole and ciclosporin is necessary, serum ciclosporin levels and serum creatinine should be closely monitored.
• Disulfiram — increased risk of acute psychoses when given with metronidazole.
• Fluorouracil — metronidazole reduces the clearance of 5-fluorouracil, increasing the risk of toxicity.
• Lithium — seek specialist advice regarding the use of metronidazole with lithium, as metronidazole increases the risk of lithium toxicity. Lithium dose reduction may be required due to the risk of renal damage with concurrent use. Plasma concentrations of lithium, creatinine, and electrolytes should be monitored if metronidazole and lithium are used simultaneously.
• Oral hormonal contraception — additional contraceptive precautions are not required during or after courses of metronidazole.
  • However, women should be advised about the importance of correct contraceptive practice if they experience vomiting or diarrhoea. For further information, see the sections on vomiting or diarrhoea in the CKS topics on Contraception - combined hormonal methods and Contraception - progestogen-only methods.
• Phenobarbital and phenytoin — the metabolism of metronidazole is increased significantly. The dose of metronidazole may need to be increased.
• Warfarin — the anticoagulant effects of warfarin may be increased by metronidazole. 
  • Monitor the international normalized ratio (INR) and adjust the warfarin dose accordingly. 
• The manufacturers SPC also notes that QT prolongation has been reported (unknown frequency), particularly when metronidazole was administered with drugs with the potential for prolonging the QT interval.

[BNF, 2022]  [CoSRH, 2022; EMC, 2023]