Previous changes

February 2025 — minor update. Detail added that if necessary, test of cure in pregnant women should be deferred for at least 3 weeks after treatment is completed.

August 2024 — minor update. Information on asymptomatic screening in people aged under 25 years has been updated in line with the National Chlamydia Screening Programme.

March 2024 — minor update. Information on the use of fluoroquinolones was added to the ofloxacin prescribing section in line with a review published by the MHRA. Fixed eruption added as an adverse effect of doxycycline as per the manufacturer's SPC.

January 2024 — minor update. Update to drug interactions section for erythromycin to include information on interactions with Lomitapide and Corticosteroids, as per the manufacturer's Summary of Product Characteristics (SPC). Information on the use of fluoroquinolones and reporting adverse reactions was added in line with the Drug Safety Update published by the MHRA.

April 2022 — minor update. Drug interactions with azithromycin to include hydroxychloroquine and chloroquine added in line with the manufacturer's summary of product characteristics.

March 2021 — reviewed. A literature search was conducted in February 2021 to identify evidence-based guidelines, UK policy, systematic reviews, and key randomized controlled trials published since the last revision of the topic. No major changes to clinical recommendations have been made.

January 2021 — minor update. Contraindications and drug interactions for erythromycin have been updated in line with an MHRA drug safety update. 

August 2020 — minor update. A reference to the BASHH Update on the treatment of Chlamydia trachomatis (CT) infection was added to the basis for recommendation in the management section of this topic. 

June 2019 — minor update. Clarification added regarding Test of cure (TOC).

March 2019 — minor update. Prescribing information for quinolones updated in line with MHRA, 2019, Fluoroquinolone antibiotics: new restrictions and precautions for use due to very rare reports of disabling and potentially long-lasting or irreversible side effects. 

February 2019 — minor update. Treatment options refined to doxycycline first line. Removed secondary care advice. 

January 2019 — minor update. Treatment options updated to be brought in line with updated BASHH guideline 2018, Chlamydia trachomatis treatment. Aortic aneurysm and dissection is now listed as an adverse effect of ciprofloxacin. 

June 2018 — minor update. Prescribing information updated with information regarding azithromycin interacting with colchicine. 

December 2016 — minor update.

• Uveitis, severe liver injury and exfoliative dermatitis were added as possible adverse effects of ofloxacin, in line with the manufacturer's updated Summary of Product Characteristics. 
• Drug reaction with eosinophilia and systemic symptoms (DRESS) has been added as a possible adverse effect of azithromycin.

June 2016 — reviewed. A literature search was conducted in June 2016 to identify evidence-based guidelines, UK policy, systematic reviews, and key randomized controlled trials (RCTs) published since the last revision of the topic. No major changes to clinical recommendations have been made.

May 2011 — minor update. The recommendation regarding the combined use of antibiotics and combined hormonal contraceptives was changed to reflect the new College of Sexual and Reproductive Healthcare guidance, Drug interactions with hormonal contraception (2011). Issued in June 2011.

September 2010 — minor update. The Health Protection Agency (HPA) figures for new diagnoses of chlamydia in 2008/9 have been added. Issued in September 2010.

August 2009 — minor update. Advice from the National Institute for Health and Care Excellence (NICE) guideline When to suspect child maltreatment (2009) has been added to this topic. Issued in August 2009.

November 2008 to May 2009 — 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. This topic now includes the management of men with uncomplicated genital chlamydia. Azithromycin is now recommended as a first-line antibiotic in women who are pregnant or breastfeeding.

September 2008 — minor correction to the Changes section. Issued in September 2008.

October to December 2005 — reviewed. Validated in March 2006 and issued in May 2006.

July 2002 — reviewed. Validated in October 2002 and issued in December 2002.

March 2000 — written. Validated in March 2000 and issued in May 2000.

New evidence

Evidence-based guidelines

No new evidence based guidelines since 1 December 2025.

HTAs (Health Technology Assessments)

No new HTAs since 1 December 2025.

Economic appraisals

No new economic appraisals relevant to England since 1 December 2025.

Systematic reviews and meta-analyses

No new systematic reviews or meta-analysis which reach the CKS threshold for inclusion since 1 December 2025.

Primary evidence

No new primary evidence which reaches the CKS threshold for inclusion published since 1 December 2025.

New policies

No new national policies or guidelines since 1 December 2025.

New safety alerts

No new safety alerts since 1 December 2025.

Changes in product availability

No changes in product availability since 1 December 2025.

Basis for recommendation

The information on groups of asymptomatic people who should be offered screening for chlamydia is based on the National chlamydia screening programme standards (eigth edition) [UKHSA, 2022], and expert opinion in clinical guidance Sexually transmitted infections in primary care [RCGP, 2013] and the UK national guideline for the management of infection with Chlamydia trachomatis (updated 2018) [BASHH, 2018].

All women seeking termination of pregnancy (TOP)

• Women undergoing TOP are at risk of ascending chlamydial infection, and so screening prior to TOP is recommended [RCGP, 2013; UKHSA, 2022].

Basis for recommendation

The recommendations on when to suspect and test for chlamydia infection are based on expert opinion in clinical guidelines Sexually transmitted infections in primary care [RCGP, 2013], the UK national guideline for the management of infection with Chlamydia trachomatis (updated 2018) [BASHH, 2018], Sexually transmitted diseases treatment guideline [CDC, 2021], and the World Health Organisation guidelines for the treatment of Chlamydia trachomatis [WHO, 2016], the 2025 European guideline on themanagement of Chlamydia trachomatis infections [White, 2025], and expert opinion in review articles [Chan, 2016; Páez‐Canro, 2019; Wong, 2019].

Basis for recommendation

The recommendations on tests for the diagnosis of chlamydia and lymphogranuloma venereum are based on the British Association for Sexual Health and HIV (BASHH) UK national guideline for the management of infection with Chlamydia trachomatis (updated 2018) [BASHH, 2018] and the Royal College of General Practitioners (RCGP) guideline Sexually transmitted infections in primary care [RCGP, 2013], and the 2025 European guideline on the management of Chlamydia trachomatis infections [White, 2025].

• No test is 100% sensitive or specific. Nucleic acid amplification tests are known to be more sensitive and specific than enzyme immunoassays (EIAs) [BASHH, 2018].
• The British Association for Sexual Health and HIV (BASHH) recommend vulvo-vaginal sample (VVS) as the specimen of choice in women (Level 11a, Grade B). VVS has a sensitivity of 96–98% and can be either taken by the person or a healthcare worker, and may pick up organisms in other parts of the genital tract. Reported sensitivities for first-catch urine (FCU) specimens in women are lower [BASHH, 2018; White, 2025].
• FCU in men is reported to be as sensitive or more sensitive than urethral sampling (Level IIa, Grade B) [BASHH, 2018; White, 2025].
• Rectal swabs and pharyngeal swabs — NAATs are the assays of choice for both genital and extra-genital samples, though the sensitivities are variable (Level IIa, Grade B) [BASHH, 2018].

Basis for recommendation

The information on the differential diagnosis of chlamydia is based on expert opinion in review articles [Van Ommen, 2023].

How should I manage a person with suspected or confirmed chlamydia?

• If chlamydia infection is suspected or confirmed, strongly recommend referral to a genito-urinary medicine (GUM) clinic for management.
  • If the person declines, or is unable to attend a GUM clinic, manage uncomplicated genital chlamydia infection in primary care.
• If a sexually transmitted infection (STI) is suspected or diagnosed in a child or young person:
  • Have a low threshold for discussing with a GUM specialist or paediatrician — local child safeguarding procedures should be followed.
  • For more information, see the CKS topic on Child maltreatment - recognition and management.
• Treat the infection
  • For non-pregnant adults and children over the age of 13 years:
    • First-line treatment is doxycycline 100 mg twice daily for 7 days (contraindicated in pregnancy and breastfeeding).
    • If doxycycline is contraindicated or not tolerated, consider azithromycin 1 g orally as a single dose for 1 day, followed by 500 mg orally once daily for 2 days.
    • If doxycycline or azithromycin are contraindicated, consider erythromycin 500 mg twice daily for 10–14 days. Ofloxacin 200 mg twice daily for 7 days, or 400 mg once daily for 7 days, is a possible alternative, but it is contraindicated in pregnancy, children, and growing adolescents. Note that systemic fluoroquinolones must now only be prescribed when other commonly recommended antibiotics are inappropriate. This follows a review by the MHRA, which assessed the effectiveness of current measures to reduce the identified risk of disabling, potentially long-lasting, or irreversible side effects.
  • For pregnant women — discuss management with other healthcare professionals involved in the woman's care (such as her midwife and obstetrician) and with GUM. Options that may be considered for treatment include:
    • • Azithromycin, 1 g orally for 1 day, then 500 mg orally once daily for 2 days, or
      • Erythromycin 500 mg four times daily for 7 days, or erythromycin 500 mg twice daily for 14 days, or
      • Amoxicillin 500 mg three times a day for 7 days.
  • If there is any uncertainty, seek specialist advice.
• Refer the person to GUM:
  • Urgently if there is no response to first-line treatment.
  • If pelvic inflammatory disease is suspected. For more information, see the CKS topic on Pelvic inflammatory disease.

What information and advice should I give the person?

• Offer written information on chlamydia, including information on transmission, treatment, possible complications, and measures to reduce the risk of further STIs. Patient information is available from:
  • The British Association for Sexual Health and HIV (BASHH) ‘A guide to - chlamydia’.
  • The Family Planning Association 'Chlamydia'.
  • If appropriate, the patient information found in the MHRA Drug Safety Update on fluoroquinolone antibiotics.
• Advise the person that:
  • Their current partner(s) must also be treated for chlamydia to reduce the risk of re-infection and onward transmission.
  • Sexual intercourse (including oral sex) should be avoided until they and their partner(s) have completed treatment (or waited 7 days after treatment with azithromycin).
  • It is strongly encouraged that all people diagnosed with chlamydia attend GUM for screening for other STIs (including gonorrhoea, hepatitis B, HIV, and syphilis) and partner notification.
    • For more information, see the CKS topics on Gonorrhoea, Hepatitis B, HIV infection and AIDS, and Syphilis.
    • If the person is unwilling or unable to attend a GUM clinic, advise them that (with their consent) their details can be provided to GUM solely for the purposes of partner notification.

How should I manage the sexual contacts of a person with chlamydia?

All patients identified with C. trachomatis should have partner notification discussed at the time of diagnosis by a trained healthcare professional, and the method of partner notification for each partner/contact identified should be documented, as should partner notification outcomes.

• Advise people diagnosed with an STI about the importance and benefits of partner notification, the possibility of sex partners being infected even if asymptomatic, and the risk of reinfection. Encourage them to engage in partner notification, regardless of where they are tested, and discuss the different methods of partner notification with them.
• Help people decide how to notify their sex partners. This includes:
  • Discussing ways of having these potentially difficult conversations and suggesting ways to deliver this information.
  • Discussing the best method of partner notification in light of the person's relationship status and other circumstances.
    • Alternative methods of disclosure may need to be used in different contexts (for example, those who may be at risk of domestic violence, or if the person expresses a need for anonymity).
• If a person feels unable to tell their sex partners about the STI or is showing signs of difficulty dealing with their diagnosis, refer them to specialist sexual health services that can offer them more support with partner notification.
• Partner notification on behalf of a person with an STI should be carried out by professionals with expertise in contact tracing and counselling, in line with the British Association for Sexual Health and HIV (BASHH) statement on partner notification for sexually transmitted infections.

How should I follow up people with chlamydia?

• Ask about adherence to treatment and resolution of symptoms.
• Check that partner notification has been carried out and reinforce health education.
• Test of cure is not routinely recommended for uncomplicated genital chlamydia infection, but is indicated in pregnancy, where poor compliance is suspected, or where symptoms persist.
  • Defer test of cure for at least 3 weeks after treatment. 
• Offer repeat testing to all people under the age of 25 years diagnosed with chlamydia 3–6 months after completion of treatment to check for re-infection.
• Consider offering repeat testing to people over the age of 25 years who are at high risk of re-infection.

What contraindications and cautions are important with amoxicillin?

Do not prescribe amoxicillin to:

• People with a true penicillin hypersensitivity.
  • 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. Reactions are more likely to occur in people with a history of penicillin hypersensitivity or atopy.
  • Gastrointestinal adverse effects alone (such as nausea, vomiting, or diarrhoea) do not constitute an allergy to penicillin.
• People with suspected infectious mononucleosis — morbilliform rash has been associated with this condition following use of amoxicillin.

Prescribe amoxicillin with caution to people with: 

• Hypersensitivity to cephalosporins.
• Renal impairment — reduce the dose of amoxicillin in severe impairment.

[EMC, 2025a; BNF, 2026]

What are the adverse effects of amoxicillin?

• Gastrointestinal — nausea and diarrhoea (common), vomiting (uncommon).
  • Rarely: antibiotic-associated colitis.
• Skin — skin rash (common), urticaria and pruritus (uncommon).
  • Very rarely: erythema multiforme, Stevens-Johnson syndrome, toxic epidermal necrolysis, bullous and exfoliative dermatitis, and acute generalized exanthematous pustulosis.
• Other rare or very rare adverse effects include:
  • Hepatitis, cholestatic jaundice.
  • Hyperkinesia, dizziness, convulsions.
  • Interstitial nephritis.
  • Leucopenia, thrombocytopenia, haemolytic anaemia.
  • Severe allergic reactions.

[EMC, 2025a; BNF, 2026]

What drug interactions are important with amoxicillin?

• Allopurinol — increased risk of rash when allopurinol is given with amoxicillin.
• Methotrexate — amoxicillin 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.
• Oral anticoagulants (warfarin, phenindione) — international normalized ratio (INR) may be increased. Monitor the INR closely during concomitant use. Dosage adjustments may be necessary. 
• Oral hormonal contraception — additional contraceptive precautions are not required during or after courses of amoxicillin.
  • 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.
• Tetracyclines — the antibacterial effects of amoxicillin may be antagonized.

[EMC, 2025a; BNF, 2026]

Pregnancy and breastfeeding

Pregnancy

• Amoxicillin is not known to be harmful in pregnancy.

Breastfeeding

• Trace amounts of amoxicillin are found in breastmilk, but it is appropriate to use in women who are breastfeeding.
• Penicillins (and cephalosporins) are the antibiotics of choice in women who are breastfeeding.

[SPS, 2024; EMC, 2025a; BNF, 2026]

What contraindications and cautions are important with azithromycin?

Prescribe azithromycin with caution to people:

• Who may be predisposed to prolongation of the QT interval. For example people:
  • With congenital or documented acquired QT prolongation.
  • Currently receiving treatment with other active substances known to prolong the QT interval such as antiarrhythmics of classes IA and III.
  • With electrolyte disturbance, particularly in cases of hypokalaemia and hypomagnesaemia.
  • With clinically relevant bradycardia, cardiac arrhythmia, or severe cardiac insufficiency, including Torsades de pointes.
• With hepatic impairment — avoid in severe impairment.
• With renal impairment.
• With myasthenia gravis — may aggravate symptoms.

[EMC, 2025b; BNF, 2026]

What are the adverse effects of azithromycin?

• Gastrointestinal — diarrhoea (very common), vomiting, abdominal pain, nausea (common).
  • Rarely: pancreatitis, pseudomembranous colitis. For more information, see the CKS topic on Diarrhoea - antibiotic associated.
• Nervous system — headache (common), dizziness, somnolence, dysgeusia, paraesthesia (uncommon).
  • Rarely: convulsions, hyperactivity, syncope, myasthenia gravis.
• Psychiatric — nervousness, insomnia (uncommon).
  • Rarely or very rarely: agitation, aggression, anxiety, delirium, hallucination.
• Skin and subcutaneous tissue — rash (common), pruritus (common), urticaria.
  • Uncommon or rare: drug reaction with eosinophilia and systemic symptoms (DRESS), Stevens-Johnson syndrome, toxic epidermal necrolysis, erythema multiforme.
• Other adverse effects reported, include:
  • Anaphylaxis.
  • Arrhythmias.
  • Arthralgia.
  • Deafness
  • Hepatitis, cholestatic jaundice.
  • Pancreatitis.
  • QT interval prolongation.

[EMC, 2025b; BNF, 2026]

What drug interactions are important with azithromycin?

• Antacids — plasma concentrations of azithromycin may be reduced. Simultaneous administration should be avoided.
  • Azithromycin should be taken at least 2 hours before, or 1 hour after antacids.
• Chloroquine and hydroxychloroquine — the manufacturer advises that clinicians carefully consider the balance of benefits and risks of co-administration due to increased risk of cardiovascular events and mortality.
• Ciclosporin — azithromycin can affect clearance of ciclosporin. If co-administration of these drugs is necessary, ciclosporin levels should be monitored and the dose adjusted accordingly.
• Colchicine — azithromycin slightly increases the levels of colchicine. Monitor for signs of colchicine toxicity (for example, nausea, vomiting, diarrhoea, myopathy, and pancytopenia).
• Digoxin — macrolides increase digoxin levels. Monitor and reduce the digoxin dose if required.
• Edoxaban — levels may be increased by azithromycin. Dose adjustment of edoxaban may be required.
• Ergot derivatives — there is a theoretical possibility of ergot toxicity if taken concomitantly with azithromycin. The manufacturer of azithromycin recommends avoiding.
• Oral hormonal contraception — additional contraceptive precautions are not required during or after courses of azithromycin.
  • 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.
• Rifabutin — azithromycin increases the risk of neutropenia when given with rifabutin. Monitor closely.
• Statins — there is a possible increased risk of myopathy.
  • Advise the person to report any muscle pain, tenderness, or weakness.
• Warfarin — occasionally and unpredictably, the effects of warfarin may be markedly increased by macrolides.
  • Monitor the international normalized ratio (INR), and adjust the warfarin dose accordingly.
• Dabigatran — azithromycin is predicted to increase the exposure to dabigatran.
• Drugs that prolong the QT interval (such as amiodarone, or sotalol) — all macrolides can prolong the QT interval, and concomitant use of drugs that prolong the QT interval is not recommended.
  • Use an alternative antibiotic and/or seek advice from a microbiologist.
• Drugs that cause hypokalaemia (such as diuretics, corticosteroids, short-acting beta-2 agonists) — hypokalaemia is a risk factor for QT prolongation.
  • Use an alternative antibiotic and/or seek advice from a microbiologist.

[CoSRH, 2022; EMC, 2025b; Preston, 2025; BNF, 2026]

Pregnancy and breastfeeding

Pregnancy

• Lack of data — manufacturer advises use only if benefit outweighs risk.

Breastfeeding

• Present in milk; use only if no suitable alternatives — manufacturer advises suspension of nursing during treatment and up to 2 days after discontinuation of treatment.

[EMC, 2025b; BNF, 2026]

What contraindications and cautions are important with doxycycline?

Do not prescribe doxycycline to:

• 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.
• Alcohol dependence.
• 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.

[BNF, 2026; EMC, 2026]

What are the adverse effects of doxycycline?

• Blood disorders — haemolytic anaemia, thrombocytopenia, neutropenia, eosinophilia (frequency unknown).
• Gastrointestinal — nausea, vomiting (common), dyspepsia (uncommon). Abdominal discomfort, diarrhoea, 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.
• Hepatic disorders — hepatotoxicity, hepatitis, jaundice, hepatic failure (frequency unknown).
• Renal disorders — blood urea increased.
• Cardiovascular disorders — hypotension, tachycardia, and peripheral oedema.
• Skin — photosensitivity, rash (common), and angioedema. Advise the person to minimize exposure to direct sunlight.
  • Rarely: toxic epidermal necrolysis, Stevens-Johnson syndrome, erythema multiforme, exfoliative dermatitis, drug reaction with eosinophilia and systemic symptoms (DRESS), and fixed eruption.
• Other adverse effects include:
  • Anaphylaxis.
  • Arthralgia, myalgia.
  • Bulging fontanelles in infants.
  • Flushing.
  • Severe headache and/or visual disturbances — may be an early symptom of benign intracranial hypertension, a rare but serious adverse effect.
  • Tinnitus.

[BNF, 2026; EMC, 2026]

What drug interactions are important 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, 2–3 hours before or after taking tetracyclines.
• CYP3A enzyme inducers (phenobarbital, carbamazepine, or phenytoin) — may reduce the serum half-life of doxycycline. Monitor and adjust the dose if necessary.
• Insulin — blood-glucose lowering effect may be increased if taken with doxycycline. Monitor blood-glucose levels.
• Lithium — levels may be increased by doxycycline. Manufacturer advises avoid or adjust dose.
• Methotrexate — levels may be increased by doxycycline; increased risk of hepatotoxicity.
• 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 are reduced, which may lead to treatment failure, dose adjustment may be needed.
• Statins — can increase risk of hepatotoxicity.
• Warfarin — concurrent use of warfarin with tetracyclines may increase the anticoagulant effect — manufacturer advises monitor international normalized ratio (INR).

[CoSRH, 2022; Preston, 2025; BNF, 2026; EMC, 2026]

Pregnancy and breastfeeding

Pregnancy

• Doxycycline is contraindicated in women who are pregnant.

Breastfeeding

• Doxycycline is contraindicated in women who are breastfeeding.

[BNF, 2026; EMC, 2026]

What contraindications and cautions are important with erythromycin?

Do not prescribe erythromycin to people:

• With porphyria.
• With a history of QT interval prolongation or ventricular cardiac arrhythmia.
• With conditions that predispose to QT interval prolongation such as electrolyte disturbances and people taking drugs that prolong the QT interval.
• With electrolyte disturbances.
• Taking medicines that interact with erythromycin (for example, simvastatin, tolterodine, mizolastine, domperidone, cisapride, pimozide, ergotamine, dihydroergotamine).

Prescribe erythromycin with caution to people with:

• Hepatic impairment (or people concomitantly receiving potentially hepatotoxic drugs).
• Moderate to severe renal impairment:
  • Give a maximum dose for erythromycin of 1.5 g a day in severe renal impairment.
• Myasthenia gravis — macrolides may aggravate weakness symptoms.

[EMC, 2025c; MHRA, 2020; BNF, 2026]

What are the adverse effects of erythromycin?

• Gastrointestinal (GI) — diarrhoea, GI discomfort/disorders, nausea, vomiting (common or very common); constipation (uncommon), pancreatitis.
  • Rare or very rare: antibiotic-associated colitis. For more information, see the CKS topic on Diarrhoea - antibiotic associated.
• Cardiovascular — QT interval prolongation, Torsades de pointes, palpitations, cardiac rhythm disorders including ventricular tachyarrhythmias.
• Hepatobiliary — cholestatic hepatitis, jaundice, hepatic dysfunction, hepatomegaly, hepatic failure, hepatocellular hepatitis.
• Skin and subcutaneous tissues — skin reactions (common or very common); angioedema, Stevens-Johnson syndrome, toxic epidermal necrolysis, erythema multiforme (uncommon); acute generalized exanthematous pustulosis (AGEP) (frequency unknown).
• Other adverse effects include:
  • Anaphylaxis.
  • Dizziness.
  • Headache.
  • Hearing impairment.
  • Vasodilation.
  • Vision disorders.

[EMC, 2025c; BNF, 2026]

What drug interactions are important with erythromycin?

• Aminophylline and theophylline — aminophylline can cause hypokalaemia (potentially increasing the risk of Torsade de pointes) when given with erythromycin. Theophylline clearance may also be reduced if given concurrently with erythromycin. Monitor theophylline levels after 48 hours and adjust the dose accordingly. Monitor potassium concentrations closely and the effects of oral erythromycin to ensure they are adequate. Consider giving an alternative antibiotic.
• Calcium channel blockers (amlodipine, diltiazem) — erythromycin possibly inhibits the metabolism of calcium channel blockers, increasing the risk of adverse effects such as hypotension. Monitor and adjust dose.
• Carbamazepine — erythromycin can increase carbamazepine levels, causing carbamazepine toxicity (which may present as nausea and vomiting, ataxia, and drowsiness).
  • Avoid concurrent use, unless carbamazepine levels can be monitored closely.
• Ciclosporin — levels are greatly increased by erythromycin. Monitor concentrations and effects (for example, renal function) more frequently if erythromycin is started or stopped.
• Colchicine — erythromycin possibly increases the risk of colchicine toxicity.
  • Stop or reduce the dose of colchicine.
  • Avoid concomitant use in renal or hepatic impairment.
• Corticosteroids — levels of corticosteroids may be increased. Monitor for corticosteroid adverse effects (such as moon face, weight gain, hyperglycaemia), and adjust the corticosteroid dose or stop the macrolide as appropriate. 
• Drugs that prolong the QT interval (such as amiodarone, amisulpride, fluconazole, lithium, sildenafil, mizolastine, hydroxyzine) — macrolides can also prolong the QT interval, increasing the risk of arrhythmias (such as Torsades de pointes).
  • Concurrent use of drugs that prolong the QT interval is not recommended.
• Drugs that cause hypokalaemia (such as diuretics, corticosteroids, short-acting beta-2 agonists) — hypokalaemia is a risk factor for QT prolongation. Monitor potassium levels closely.
• Digoxin — erythromycin may increase the concentration of digoxin.
  • Monitor digoxin concentration.
• Ergot alkaloids (such as ergotamine and dihydroergotamine) — concurrent use with erythromycin may result in acute ergot toxicity.
  • Concurrent use is contraindicated.
• Lomitapide — concurrent use with erythromycin increases transaminase levels and is contraindicated.
• Protease inhibitors (ritonavir, saquinavir) — erythromycin levels may be increased. Monitor for adverse effects.
• Rifampicin — may induce the metabolism of clarithromycin, resulting in sub-therapeutic levels.
  • If concurrent use is necessary, monitor erythromycin efficacy closely.
• Statins — there is an increased risk of myopathy (due to cytochrome P450 enzyme CYP3A4 inhibition).   
  • Simvastatin (potent CYP3A4 inhibitor) — concurrent use is contraindicated. If erythromycin treatment cannot be avoided, stop treatment with simvastatin during the course of the treatment.
  • Atorvastatin (moderate CYP3A4 inhibitor) — avoid concurrent use if possible. If erythromycin treatment cannot be avoided, prescribe the lowest starting dose of atorvastatin (that is 10 mg) and do not exceed 20 mg atorvastatin daily. Advise the person to seek medical advice if they experience symptoms of myopathy (for example, muscle pain, tenderness, or weakness).
  • Pravastatin — prescribe erythromycin with caution, and advise the person to report any muscle pain, tenderness, or weakness.
• Quetiapine — erythromycin increases the plasma concentration of quetiapine, and both drugs are associated with QT interval prolongation.
  • Concurrent use is contraindicated, but if necessary, monitor for quetiapine adverse effects (for example, somnolence, dry mouth, tachycardia) and reduce the dose if needed.
• Oral anticoagulants such as:
  • Rivaroxaban — erythromycin may increase levels of rivaroxaban, increasing the risk of bleeding.
  • Warfarin — erythromycin may cause a minor increase in warfarin effects. Consider increased monitoring of the international normalized ratio (INR) when both drugs are used (particularly in elderly people), and adjust the warfarin dose accordingly.
• Oral hormonal contraception — additional contraceptive precautions are not required during or after a course of erythromycin.
  • However, advise women on the importance of correct contraceptive practice if they experience vomiting or diarrhoea. For further information, see the section on vomiting or diarrhoea in the CKS topics on Contraception - combined hormonal methods and Contraception - progestogen-only methods.

[MHRA, 2020; EMC, 2025c; Preston, 2025; BNF, 2026]

Pregnancy and breastfeeding

Pregnancy

• The use of erythromycin in pregnancy is not known to be harmful — the considerable data for macrolides as a class, and for erythromycin specifically, do not suggest an increased overall risk of congenital malformation or of cardiac malformations specifically.
• However, the manufacturer states that:
  • Observational studies in humans have reported cardiovascular malformations after exposure to medicinal products containing erythromycin during early pregnancy.
  • There have been reports that maternal macrolide antibiotics exposure within 7 weeks of delivery may be associated with a higher risk of infantile hypertrophic pyloric stenosis (IHPS).

Breastfeeding

• Erythromycin is excreted in breast milk in small amounts and it is not known to be harmful.
  • Monitor the infant for irritability and possible effects on the gastrointestinal flora, such as diarrhoea, candidiasis (thrush, nappy rash).
• The manufacturer advises exercising caution due to reports of infantile hypertrophic pyloric stenosis in breastfed infants.

[UKTIS, 2020; LactMed, 2024; EMC, 2025c; BNF, 2026]

What contraindications and cautions are important with ofloxacin?

Note that systemic fluoroquinolones must now only be prescribed when other commonly recommended antibiotics are inappropriate. This follows a review by the MHRA which looked at the effectiveness of current measures to reduce the identified risk of disabling and potentially long-lasting or irreversible side effects.

Do not prescribe ofloxacin in:

• Children or growing adolescents.
• Women who are pregnant or breastfeeding.
• People with glucose-6-phosphate dehydrogenase deficiency.
• People with a history of tendon disorders related to fluoroquinolone administration, or who have previously had serious adverse reactions with a quinolone or fluoroquinolone antibiotic.
• People who are taking a corticosteroid — co-administration could exacerbate fluoroquinolone-induced tendonitis and tendon rupture.
• Myasthenia gravis — symptoms can be exacerbated.

Prescribe ofloxacin with caution in people with:

• Aortic aneurysm and/or aortic dissection, a family history of aneurysm disease, or with risk factors or conditions predisposing for aortic aneurysm and dissection (for example, Marfan syndrome, vascular Ehlers-Danlos syndrome, Takayasu arteritis, giant cell arteritis, Behcet's disease, hypertension, known atherosclerosis) — consider other therapeutic options.
• Congenital or pre-existing heart valve disease or risk factors predisposing to heart valve disease.
• Diabetes mellitus — may affect blood glucose. Blood glucose should be monitored closely.
• Epilepsy, or conditions that predispose to seizures, and in people taking other medications that may predispose to seizures, such as quinolones, can lower the seizure threshold.
• Quinolones may induce convulsions in patients with or without a history of convulsions, and taking nonsteroidal anti-inflammatory drugs at the same time may also induce them.
• A history of tendonitis — quinolones can very rarely cause tendon damage, and the risk of tendon rupture is increased by co-administration of corticosteroids.
• Impaired liver function — liver damage can occur.
• Impaired renal function — dose adjustments may be required.
• Conditions that predispose to QT interval prolongation:
  • Congenital long QT syndrome.
  • Concurrent use of drugs that are known to prolong the QT interval (for example, Class IA and III anti-arrhythmics, tricyclic antidepressants, macrolides, antipsychotics).
  • Uncorrected electrolyte imbalance (for exampl,e hypokalaemia or hypomagnesaemia).
  • Cardiac disease (for example, heart failure, myocardial infarction, or bradycardia).
  • Electrolyte disturbances.
• History of a psychotic disorder — there have been reports of suicidal thoughts or self-endangering behaviour after use of quinolones.
• An age greater than 60 years, renal impairment, or solid-organ transplants, as these people are at a higher risk of tendon injury.

[MHRA, 2019; MHRA, 2023; EMC, 2025d; BNF, 2026]

What are the adverse effects of ofloxacin?

• Cardiovascular system — tachycardia (rarely); ventricular arrhythmias, Torsades de pointes, QT interval prolongation (frequency unknown), heart valve regurgitation.
  • There is an increased risk of aortic aneurysm and dissection with fluoroquinolones, particularly in the older population. Fluoroquinolones should only be used after careful benefit-risk assessment and after consideration of other therapeutic options in people with positive family history of aneurysm disease, or in people diagnosed with pre-existing aortic aneurysm and/or aortic dissection, or in presence of other risk factors or conditions predisposing for aortic aneurysm and dissection (for example, Marfan syndrome, vascular Ehlers-Danlos syndrome, Takayasu arteritis, giant cell arteritis, Behcet’s disease, hypertension, known atherosclerosis).
• Gastrointestinal — diarrhoea, constipation, nausea, vomiting, abdominal pain (uncommon).
  • Very rarely: pseudomembranous colitis. For more information, see the CKS topic on Diarrhoea - antibiotic associated.
• Musculoskeletal — tendonitis (rare).
  • Arthralgia, myalgia, tendon rupture — this may occur within 48 hours of starting treatment, or months after stopping. Risk of tendon rupture is increased by co-administration of corticosteroids and in people aged over 60 years. If tendonitis is suspected, ciprofloxacin should be discontinued immediately.
• Nervous system — headache, dizziness.
  • Rarely: sleep disorders, taste disorders, tremor, vertigo, lowering of the seizure threshold — this may trigger seizures.
• Psychiatric — agitation, sleep disorder, insomnia.
  • Rarely: confusion, anxiety, depression, nightmares, suicidal behaviours.
• Skin — rash, pruritus (uncommon).
  • Exposure to excessive sunlight and UV radiation should be avoided during treatment and for 48 hours after stopping treatment.
  • Rarely: angioedema, Stevens-Johnson syndrome, erythema multiforme, toxic epidermal necrolysis anaphylaxis, drug rash with eosinophilia, systemic symptoms (DRESS), acute generalized exanthematous pustulosis (AGEP).
• Other adverse effects include:
  • Anaphylaxis.
  • Dyspnoea, bronchospasm.
  • Hepatic impairment, hepatitis.
  • Renal impairment.
  • Tachycardia.
  • Tinnitus.
  • Bone marrow failure.
  • Visual disturbances.
• Fluoroquinolones can very rarely cause long-lasting (up to months or years), disabling, and potentially irreversible side effects, sometimes affecting multiple systems, organ classes, and senses.
  • People should be advised to stop treatment at the first signs of a serious adverse reaction, such as tendonitis or tendon rupture, muscle pain, muscle weakness, joint pain, joint swelling, peripheral neuropathy, and central nervous system effects, and to contact their doctor immediately for further advice. Remain alert to the risk of suicidal thoughts and behaviours with use of fluoroquinolone antibiotics. 

[MHRA, 2019; MHRA, 2023; EMC, 2025d; BNF, 2026]

What drug interactions are important with ofloxacin?

• Antacids (containing aluminium, calcium, or magnesium) and other medications containing iron or zinc — these may reduce the absorption of ofloxacin if taken concurrently.
  • Ofloxacin should be taken at least 2 hours before these preparations, and not less than 4–6 hours after them.
• Corticosteroids — the risk of tendonitis and tendon rupture is increased in people taking a fluoroquinolone and a corticosteroid. The MHRA advises that concurrent use should be avoided.
• Ergometrine — levels may be increased, leading to ergotism. Concurrent use is contraindicated.
• Nonsteroidal anti-inflammatory drugs (NSAIDs) — possible increased risk of seizures when quinolones are given with NSAIDs. Avoid concurrent use in people with epilepsy or people predisposed to seizures, or monitor them very closely.
• Oral hormonal contraception — additional contraceptive precautions are not required during or after courses of ofloxacin.
  • 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.
• Strontium ranelate — the absorption of quinolones is reduced by strontium ranelate so they should not be given together.
• Theophylline — ciprofloxacin increases the plasma concentration of theophylline, leading to possible increased risk of convulsions. There is the possibility of a similar effect with ofloxacin. Monitor theophylline concentration closely.
• Warfarin — ofloxacin may enhance the anticoagulant effect, increasing the risk of bleeding. Monitor international normalized ratio (INR).
• Zolmitriptan — quinolones increase the plasma concentration of zolmitriptan by inhibiting its metabolism. The manufacturer recommends a maximum dose of 5 mg in 24 hours in people taking a quinolone.
• Drugs that prolong the QT interval (such as Class IA and III anti-arrhythmics, tricyclic antidepressants, macrolides, and antipsychotics) — very rare cases of QT interval prolongation have been reported in people taking quinolones and they should therefore be prescribed with caution alongside drugs known to prolong the QT interval.

[MHRA, 2019; CoSRH, 2022; MHRA, 2023; EMC, 2025d; Preston, 2025; BNF, 2026]

Pregnancy and breastfeeding

Pregnancy

• The use of ofloxacin in women who are pregnant is not recommended.

Breastfeeding

• Ofloxacin is excreted in breastmilk in quantities that are probably too small to be harmful, however the manufacturer advises avoid.

[MHRA, 2019; EMC, 2025d; BNF, 2026]