Previous changes

February 2025 — minor update. Duration of antibiotic treatment updated to 5–7 days.  

May 2024 — minor update. Information added stating that concomitant treatment with clarithromycin and ivabradine is now contra-indicated and caution is now advised when co-administering clarithromycin with edoxaban, as per the manufacturer's updated SPC.

December 2023 — 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).

November 2023 — minor update. Interactions section for flucloxacillin updated in line with updated manufacturer's summary of product characteristics.

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

December 2016 — minor update. The dose of clarithromycin for people with severe renal impairment has been clarified, in line with the manufacturer's Summary of Product Characteristics.

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

July 2015 — minor update. The prescribing information sections on erythromycin and clarithromycin have 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.

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. Issued in July 2011.

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

April 2011 — minor update. Change to recommendation regarding need for additional contraception during or after a course of antibiotics - additional contraception is no longer required when using antibiotics that are not enzyme inducers with combined hormonal methods for durations of 3 weeks or less. Issued in June 2011

November 2010 to March 2011 — CKS topic revised. The evidence-base has been reviewed in detail, and recommendations are more clearly justified and transparently linked to the supporting evidence. This CKS topic replaces the former topic on Boils and paronychia, which included the management of staphylococcal whitlow. There are now separate CKS topics on Boils, carbuncles, and staphylococcal carriage and Paronychia - acute. This topic now includes the management of herpetic whitlow.

July 2007 — Oilatum Plus discontinued. Minor change to the text made and prescriptions removed. Issued in August 2007.

December 2006 to March 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.

October 2006 — minor update. Analgesia prescriptions updated because new doses of ibuprofen for children are recommended by the British National Formulary. Issued in October 2006.

October 2005 — minor technical update. Issued in November 2005.

September 2003 — written. Validated in December 2003 and issued in February 2004.

New evidence

Evidence-based guidelines

No new evidence-based guidelines since 1 February 2026.

HTAs (Health Technology Assessments)

No new HTAs since 1 February 2026.

Economic appraisals

No new economic appraisals relevant to England since 1 February 2026.

Systematic reviews and meta-analyses

No new systematic reviews or meta-analysis which reach the CKS threshold for inclusion since 1 February 2026.

Primary evidence

No new primary evidence which reaches the CKS threshold for inclusion published since 1 February 2026.

New policies

No new national policies or guidelines since 1 February 2026.

New safety alerts

No new safety alerts since 1 February 2026.

Changes in product availability

No changes in product availability since 1 February 2026.

Basis for recommendation

The recommendations on the diagnosis of staphylococcal and herpetic whitlow are based on expert opinion in review articles [McDonald, 2011; Rigopoulos, 2012; Sanders, 2014; Barabas, 2015; Rerucha, 2019; DermNet, 2023; Barger, 2024; Iorizzo, 2024], a chapter within a textbook on musculoskeletal infections [Lee, 2020], and chapters within dermatology textbooks [Craft, 2008; de Berker, 2010].

Basis for recommendation

The recommendations on the differential diagnosis of staphylococcal and herpetic whitlow are based on expert opinion in review articles  [Rerucha, 2019; DermNet, 2023; Barger, 2024; Iorizzo, 2024].

How should I manage a person with staphylococcal whitlow?

• Urgently admit the person to hospital if there are systemic features (for example, fever, tachycardia, or signs of shock), or associated lymphadenopathy or ascending lymphangitis.
• Consider arranging same-day incision and drainage for people with a whitlow that is tense (even when a frank abscess has not developed) or fluctuant (the lesion feels 'boggy', and the overlying skin has a shiny appearance). 
  • The decision on whether to arrange same-day incision and drainage will depend on clinical judgement, taking into account the rapidity and degree of spread; any underlying comorbidities, such as conditions causing immunosuppression; and whether the person (or their carer) is able to follow instructions reliably regarding monitoring for complications.
  • Incision and drainage may be performed in primary care if the expertise and facilities are available. Otherwise refer to a surgical unit or emergency department, according to local protocols.
• If incision and drainage are not indicated:
  • Consider prescribing oral antibiotics. 
    • Flucloxacillin is recommended first line. 
    • Erythromycin or clarithromycin are alternatives if the person has a true allergy to penicillin. Prescribe erythromycin to women who are pregnant or breastfeeding.
  • For more information, see Prescribing information.
  • Seek specialist advice if the person is already known to have meticillin-resistant Staphylococcus aureus (MRSA) infection or a swab sample grows MRSA.
• Consider taking a swab from the contents of the whitlow if:
  • The whitlow is recurrent.
  • The person is immunosuppressed or at increased risk of infection.
  • The whitlow has not responded to treatment within 2–3 days.
  • The person has a history of MRSA infection or contact with MRSA. For more information, see the CKS topic on MRSA in primary care.
  • There is doubt about the diagnosis.
• Consider referral for an X-ray if there is a history of injury and the possibility of a radio-opaque foreign body. Osteomyelitis can occur as a rare complication of staphylococcal whitlow; sinus tract formation may be associated with osteomyelitis and requires x-ray investigation.
• Consider the need for tetanus prophylaxis.
• Advise the person to:
  • Keep the finger elevated as much as possible.
  • Apply moist heat three to four times a day to alleviate pain and hasten draining of the pus.
  • Take paracetamol or ibuprofen as required for pain relief. For more information, see the CKS topics on Analgesia - mild-to-moderate pain and NSAIDs - prescribing issues.
  • Reduce the risk of recurrence by avoiding , such as injuries to the fingertips.
  • Seek medical advice if:
    • Swelling and pain become worse, or the whitlow becomes fluctuant (incision and drainage may be necessary).
    • They become systemically unwell (admission for intravenous antibiotics may be necessary).
    • The whitlow recurs (a swab for bacterial culture may be necessary).

How should I manage a person with herpetic whitlow?

• Wear protective gloves when touching a person with active symptoms of herpes, such as an open, fluid-filled blister.
• Consider prescribing an antiviral drug if the person presents soon after the onset of symptoms (for example, within 48 hours). Aciclovir is recommended first line. For more information, see Prescribing information.
  • Antiviral drugs can be used to treat recurrent episodes if they are initiated within 48 hours of the onset of symptoms.
• Incision and drainage of a herpetic lesion are not recommended.
• Consider taking a swab for:
  • Virological culture if the diagnosis is uncertain, the whitlow does not resolve with treatment or is recurrent, or the person is immunocompromised.
  • Bacterial culture if secondary bacterial infection is suspected.
• Advise the person (where appropriate) to:
  • Take paracetamol or ibuprofen as required for pain relief. For more information, see the CKS topics on Analgesia - mild-to-moderate pain and NSAIDs - prescribing issues.
  • Avoid touching the infected area.
  • Ensure that the infected finger is covered with a clean, dry dressing to prevent transmission.
  • Avoid touching other parts of their body with the affected finger, especially the eyes. They should avoid wearing contact lenses (instead, wear glasses) until the infection has healed.
  • Discourage affected children from sucking their thumbs.
• Offer written information. Patient information on herpetic whitlow is available from the NHS.
• Inform the person that recurrence is common, but the initial infection is usually the most severe.
  • Offer HIV (human immunodeficiency virus) testing if the lesion is particularly extensive. For more information, see the CKS topic on HIV infection and AIDS.
• Where appropriate, manage the underlying cause of the herpetic whitlow. For more information, see the CKS topics on Herpes simplex - genital and Herpes simplex - oral.

What dose of aciclovir should I prescribe?

• For adults and children from 2 years of age — prescribe 200 mg five times daily (at approximately 4-hourly intervals during the day, omitting the nighttime dose) for 5 days.
• For children 1 month to 23 months — prescribe 100 mg five times daily (at approximately 4-hourly intervals during the day, omitting the nighttime dose) for 5 days.
• For immunocompromised adults and children, the dose should be doubled:
  • Adults and children from 2 years of age — prescribe 400 mg five times daily for 5 days.
  • Children 1 month to 23 months — prescribe 200 mg five times daily for 5 days.

[EMC, 2025c; BNF, 2026; BNFC, 2026]

What are the contraindications and cautions for aciclovir?

• Do not prescribe aciclovir to a person with a known allergy to aciclovir or valaciclovir.
• Prescribe aciclovir with caution in a person who: 
  • Is elderly.
  • Has renal impairment — advise the person to maintain adequate hydration. For herpes simplex infection, use the normal oral dose twice daily (every 12 hours) if the person's estimated glomerular filtration rate (eGFR) is less than 10 mL/minute/1.73 m².

[EMC, 2025c; BNF, 2026; BNFC, 2026]

What are the adverse effects of aciclovir?

• Aciclovir is generally well tolerated. 
• However, it may cause gastrointestinal adverse effects, such as nausea, vomiting, diarrhoea, and abdominal pain. Headache, dizziness, and skin rashes (including photosensitivity and urticaria) have also been commonly reported.

[EMC, 2025c; BNF, 2026; BNFC, 2026]

What are the drug interactions with aciclovir?

Clinically relevant drug interactions with aciclovir include:

• Aminophylline and theophylline — levels of these drugs are increased if used concurrently with aciclovir. Measurement of plasma concentrations and dose adjustment where necessary are therefore recommended.
• Nephrotoxic drugs — Use with other nephrotoxic drugs increases the risk of renal impairment. Examples include, but are not limited to, colistimethate, nonsteroidal anti-inflammatory drugs, tacrolimus,  and voclosporin.
• Live herpes-zoster vaccine — vaccine efficacy may be affected. Avoid live herpes-zoster vaccines until at least 48 hours after stopping aciclovir. If possible, avoid aciclovir for 2 weeks after live herpes-zoster vaccines.

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

What dose of clarithromycin should I prescribe?

• Adults: 250 mg to 500 mg twice daily for 5–7 days.
• Children aged:
  • 1 month to 11 years with body weight:
    • Less than 8 kg: 7.5 mg per kg twice daily for 5–7 days.
    • 8–11 kg: 62.5 mg twice daily for 5–7 days.
    • 12–19 kg: 125 mg twice daily for 5–7 days.
    • 20–29 kg: 187.5 mg twice daily for 5–7 days.
    • 30–40 kg: 250 mg twice daily for 5–7 days.
  • 12 years and over:  250 mg to 500 mg twice daily for 5–7 days.

[EMC, 2024; BNF, 2026]

What are the contraindications and cautions for clarithromycin?

• Do not prescribe clarithromycin to people with:
  • Known hypersensitivity to clarithromycin or other macrolide antibiotics.
  • A history of QT prolongation or ventricular arrhythmia, including Torsade de Pointes.
  • Hypokalaemia or hypomagnesaemia.
  • Severe hepatic failure.
• Clarithromycin is also contraindicated for people taking certain drugs.
• Prescribe clarithromycin with caution in people with:
  • Coronary artery disease, severe cardiac insufficiency, or bradycardia (less than 50 beats per minute) — increased risk of QT prolongation.
  • Other conditions that predispose to QT interval prolongation, such as electrolyte disturbances and people taking drugs that prolong the QT interval  — macrolides can also prolong the QT interval, increasing the risk of Torsades de Pointes arrhythmia. 
  • Impaired hepatic function (or people concomitantly receiving potentially hepatotoxic drugs) — clarithromycin is principally excreted by the liver. Hepatic dysfunction, including increased liver enzymes and cholestatic hepatitis (with or without jaundice) has been rarely reported with clarithromycin.
  • Use half the normal dose in severe renal impairment (estimated glomerular filtration rate [eGFR] less than 30 mL/min/1.73 m²) for a maximum duration of 14 days.
    • Avoid Xetinin XL^® (clarithromycin 500 mg modified release once daily tablets) in people with eGFR less than 30 mL/min/1.73  m², and use half the normal dose of modified release tablets in people with eGFR between 30 and 60 mL/min/1.73 m².
  • Myasthenia gravis — macrolide antibiotics may aggravate weakness symptoms of people with myasthenia gravis.
  • Concurrent conditions treated with drugs metabolised by CYP3A enzymes, particularly where the drug has a narrow safety margin.
    • Examples include, but are not limited to, alprazolam, cilostazol, ciclosporin, disopyramide, ibrutinib, methadone, methylprednisolone, omeprazole, atypical antipsychotics, quinidine, rifabutin, sildenafil, sirolimus, tacrolimus, triazolam and vinblastine.

[EMC, 2024; BNF, 2026; EMC, 2026]

What are the adverse effects of clarithromycin?

• Clarithromycin is generally well tolerated. 
• The most common adverse effects are gastrointestinal — such as nausea, vomiting, dyspepsia, and diarrhoea.
  • Consider pseudomembranous colitis if a person develops severe diarrhoea during or after treatment with clarithromycin.
  • Pseudomembranous colitis is an acute, exudative colitis caused by Clostridiodes difficile, a Gram-positive toxin-releasing bacillus. It often follows antibiotic treatment. For more information, see the CKS topic on Diarrhoea - antibiotic associated.
• Less common adverse effects include muscle complaints (spasms, stiffness and myalgia), rash and hepatoxicity.
• Very rarely, QT prolongation, ventricular tachycardia, and Torsade de Pointes arrhythmia have been reported.

[EMC, 2024; BNF, 2026]

What are the important drug interactions with clarithromycin?

• Drug interactions with clarithromycin include:
  • Pimozide — do not prescribe with clarithromycin as concurrent use may result in QT prolongation, cardiac arrhythmias including ventricular tachycardia, ventricular fibrillation, and Torsade de Pointes.
  • Ergotamine and dihydroergotamine — do not prescribe with clarithromycin as concurrent use may result in acute ergot toxicity. 
  • Colchicine — avoid concomitant administration.
  • Carbamazepine — monitor carbamazepine levels within 3–5 days of starting clarithromycin, and adjust dose accordingly. Clarithromycin can increase carbamazepine levels, causing carbamazepine toxicity (may present as nausea and vomiting, ataxia, and drowsiness).
  • Phenytoin and valproate — Clarithromycin can increase phenytoin and valproate levels.
  • Digoxin — elevated digoxin serum concentrations have been observed in people receiving clarithromycin and digoxin concomitantly, with some displaying clinical signs of digoxin toxicity.
  • Edoxaban — manufacturer advises caution with concurrent treatment with edoxaban, particularly in those with a high risk of bleeding.
  • Ivabradine — concomitant treatment is contraindicated, owing to CYP3A4 inhibition by clarithromycin which can cause elevated levels of ivabradine.
  • Lomitapide — concurrent use with clarithromycin increases transaminase levels and is contraindicated.
  • Midazolam — concomitant treatment is contraindicated as this can result in elevated levels of midazolam.
  • Other drugs that prolong the QT interval — if possible, avoid giving clarithromycin to a person who is already taking a drug that can potentially prolong the QT interval. These include, but are not limited to, astemizole, cisapride, domperidone and terfenadine.
  • Ranolazine — concomitant treatment is contraindicated as clarithromycin is predicted to markedly increase ranolazine levels.
  • Statins — there is an increased risk of myopathy.
    • For simvastatin — do not prescribe clarithromycin to a person taking simvastatin. Consider temporarily stopping simvastatin during short-term treatment with clarithromycin. 
    • For atorvastatin — avoid concurrent use with clarithromycin if possible. Consider temporarily stopping atorvastatin during short-term treatment with clarithromycin. If concurrent use cannot be avoided, prescribe the lowest starting dose of atorvastatin (10 mg), and advise the person to report any muscle pain, tenderness, or weakness.
    • For pravastatin — prescribe clarithromycin with caution and advise the person to seek medical advice if they experience symptoms of myopathy (for example muscle pain, tenderness, or weakness).
    • Other statins — clinically significant interaction with clarithromycin is not expected for rosuvastatin and fluvastatin. Nevertheless, advise the person to report any muscle pain, tenderness, or weakness. 
  • Ticagrelor — concomitant treatment is contraindicated as clarithromycin is predicted to markedly increase ticagrelor levels.
  • Warfarin — increase monitoring of the international normalized ratio (INR) when both drugs are used (particularly in elderly people), and adjust the warfarin dose accordingly. Clarithromycin may enhance the effect of warfarin. 
  • Zidovudine — concurrent use can decrease steady-state zidovudine concentrations.
  • Oral hypoglycaemic drugs and insulin — the concurrent use of clarithromycin and antidiabetic drugs (such as sulphonylureas and/or insulin) can result in significant hypoglycaemia.
    • Monitor blood glucose levels more regularly and adjust the antidiabetic drug (and/or insulin) dose accordingly. 
  • Calcium channel blockers (CCBs) — due to an increased risk of hypotension, caution is advised with the concurrent use of clarithromycin and CCBs metabolized by CYP3A4 (such as verapamil, amlodipine, and diltiazem).
  • Drugs that cause hypokalaemia (such as diuretics, corticosteroids, short-acting beta-2 agonists) — hypokalaemia is a risk factor for QT prolongation.
  • Oral hormonal contraception — additional contraceptive precautions are not required during or after courses of clarithromycin.
    • However, women should be advised about the importance of correct contraceptive practice if they experience vomiting or diarrhoea. For further information, see the CKS topic on Contraception - assessment.
  • Other drugs metabolised by CYP3A enzymes — particularly where the drug has a narrow safety margin.
    • Examples include, but are not limited to, alprazolam, cilostazol, ciclosporin, disopyramide, ibrutinib, methadone, methylprednisolone, omeprazole, atypical antipsychotics, quinidine, rifabutin, sildenafil, sirolimus, tacrolimus, triazolam and vinblastine.

[CoSRH, 2022; EMC, 2024; BNF, 2026; Preston, 2026]

What dose of erythromycin should I prescribe?

• Adults: 250 mg to 500 mg four times daily for 5–7 days.
• Children aged:
  • 1–23 months: 125 mg four times daily for 5–7 days.
  • 2–7 years: 250 mg four times daily for 5–7 days.
  • 8–17 years: 250 mg to 500 mg four times daily for 5–7 days.

[BNF, 2026]

What are the contraindications and cautions for erythromycin?

• Do not prescribe erythromycin to people with:
  • Porphyria or a known hypersensitivity to erythromycin.
  • A history of QT interval prolongation or ventricular cardiac arrhythmia.
  • Conditions that predispose to QT interval prolongation such as electrolyte disturbances and people taking drugs that prolong the QT interval.
• Erythromycin is also contraindicated for people taking certain drugs.
• Prescribe erythromycin with caution in people with:
  • Impaired hepatic function (or people concomitantly receiving potentially hepatotoxic drugs) — erythromycin is principally excreted by the liver. 
  • Renal impairment — some manufacturers advise dose reduction in severe renal impairment.
  • Myasthenia gravis — macrolide antibiotics may aggravate weakness symptoms of people with myasthenia gravis.

[EMC, 2025b; BNF, 2026]

What are the adverse effects of erythromycin?

• Gastrointestinal adverse effects such as nausea, vomiting, and diarrhoea are common in people taking erythromycin.
  • Consider pseudomembranous colitis if a person develops severe diarrhoea during or after treatment with erythromycin.
  • Pseudomembranous colitis is an acute, exudative colitis caused by Clostridiodes difficile, a Gram-positive toxin-releasing bacillus. It often follows antibiotic treatment. For more information, see the CKS topic on Diarrhoea - antibiotic associated.
• Hepatic dysfunction, including increased liver enzymes and cholestatic hepatitis (with or without jaundice), has been rarely reported with this drug.

[EMC, 2025b; BNF, 2026]

What are the important drug interactions with erythromycin?

• Drug interactions with erythromycin include:
  • Tolterodine, mizolastine, amisulpride, astemizole, terfenadine, domperidone, cisapride, ergotamine, dihydroergotamine, and pimozide — concurrent administration with erythromycin is contraindicated.
  • Cimetidine — monitor concurrent use closely as a dose reduction of erythromycin may be necessary. Cimetidine may inhibit the metabolism of erythromycin, leading to an increased plasma concentration.
  • Calcium channel blockers (CCBs) — due to an increased risk of hypotension, caution is advised with the concurrent use of erythromycin and CCBs metabolized by CYP3A4 (such as verapamil).
  • Carbamazepine — monitor carbamazepine levels within 3–5 days of starting erythromycin and adjust the dose accordingly. Erythromycin can increase carbamazepine levels, causing carbamazepine toxicity (which may present as nausea and vomiting, ataxia, and drowsiness).
  • Colchicine — avoid concurrent use if possible. Colchicine toxicity has been reported following concomitant use with erythromycin.
  • 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 — if possible, avoid giving erythromycin to a person who is already taking a drug that can potentially prolong the QT interval.
  • Ivabradine — levels of ivarbradine may be increased when used concurrently with erythromycin and is contraindicated, and rare cases of serious, potentially fatal, cardiovascular events including cardiac arrest, torsade de pointes and other ventricular arrhythmias have been observed.
  • Lomitapide — concurrent use with erythromycin increases transaminase levels and is contraindicated.
  • Statins — there is an increased risk of myopathy.
    • For simvastatin — do not prescribe erythromycin to a person taking simvastatin. Consider temporarily stopping simvastatin during short-term treatment with erythromycin. 
    • For atorvastatin — avoid concurrent use with erythromycin if possible. Consider temporarily stopping atorvastatin during short-term treatment with erythromycin. If concurrent use cannot be avoided, prescribe the lowest starting dose of atorvastatin (10 mg), and advise the person to report any muscle pain, tenderness, or weakness.
    • For pravastatin — prescribe erythromycin with caution and advise the person to seek medical advice if they experience symptoms of myopathy (for example muscle pain, tenderness, or weakness).
    • Other statins — clinically significant interaction with erythromycin is not expected for rosuvastatin and fluvastatin. Nevertheless, advise the person to report any muscle pain, tenderness, or weakness. 
  • Terfenadine — concurrent use with erythromycin may affect terfenadine metabolism.
  • Theophylline — consider using clarithromycin (in preference to erythromycin) as clarithromycin normally causes only modest (clinically unimportant) increases in theophylline levels.
    • Concurrent use of erythromycin with high doses of theophylline may be associated with an increase in serum theophylline levels and potential theophylline toxicity (which may present as palpitations, nausea, tremor, and headache). If this is suspected, reduce the dose of theophylline. 
    • Concurrent treatment may also result in a significant decrease in erythromycin serum concentrations, leading to sub-therapeutic concentrations of erythromycin.
  • Triazolobenzodiazepines and related benzodiazepines — such as alprazolam, triazolam and midazolam, concurrent use with erythromycin may decrease clearance and increase the pharmacological effect of these drugs.
  • Rivaroxaban — erythromycin may increase levels of rivaroxaban, increasing the risk of bleeding. 
  • Warfarin — monitor the international normalized ratio (INR) when both drugs are used (particularly in elderly people), and adjust the warfarin dose accordingly. Erythromycin may enhance the effect of warfarin; this is an established but unpredictable interaction.
  • Zopiclone — monitor concurrent use. Erythromycin has been reported to decrease the clearance of zopiclone and this may lead to an increase in the effects of zopiclone. 
  • Oral hormonal contraception — additional contraceptive precautions are not required during or after courses of erythromycin.
    • However, women should be advised about the importance of correct contraceptive practice if they experience vomiting or diarrhoea. For further information, see the CKS topic on Contraception - assessment.

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

What dose of flucloxacillin should I prescribe?

• Adults: 250 mg to 500 mg four times daily for 5–7 days.
• Children aged:
  • 1 month to 1 year: 62.5 mg to 125 mg four times daily for 5–7 days.
  • 2–9 years: 125 mg to 250 mg four times daily for 5–7 days.
  • 10–17 years: 250 mg to 500 mg four times daily for 5–7 days.

[BNF, 2026]

What are the contraindications and cautions for flucloxacillin?

• Do not prescribe flucloxacillin to people with:
  • A true penicillin allergy — gastrointestinal adverse effects alone (for example nausea, vomiting, or diarrhoea) do not constitute an allergy to penicillin.
  • History of flucloxacillin-associated jaundice or hepatic dysfunction.
• Prescribe flucloxacillin with caution to people with: 
  • Hepatic dysfunction (not flucloxacillin-related), especially if they are 50 years of age or older, or have a serious underlying medical condition.
  • Severe renal impairment — reduce the dose if the person's estimated glomerular filtration rate (eGFR) is less than 10 mL/minute/1.73 m².

[EMC, 2025a; BNF, 2026]

What are the adverse effects of flucloxacillin?

• Diarrhoea is a common adverse effect of flucloxacillin.
  • Consider pseudomembranous colitis if a person develops severe diarrhoea during or after treatment with flucloxacillin.
  • Pseudomembranous colitis is an acute, exudative colitis caused by Clostridiodes difficile, a Gram-positive toxin-releasing bacillus. It often follows antibiotic treatment. For more information, see the CKS topic on Diarrhoea - antibiotic associated.
• Cholestatic jaundice and hepatitis may occur (very rarely) up to several weeks after treatment with flucloxacillin has been stopped. Risk factors include treatment for more than 2 weeks and increasing age.
• Uncommon adverse effects include arthralgia, leucopenia, rash, urticaria and purpura.

[EMC, 2025a; BNF, 2026]

What are the drug interactions with flucloxacillin?

• Methotrexate — methotrexate clearance may be reduced, causing an increased risk of toxicity; however, serious interactions are uncommon. 
  • Standard routine monitoring will identify any decreases in elimination in people on high-dose regimens. For people on low-dose regimens, consult local or national guidelines/protocols for monitoring and management.
• Coumarin and indanedione anticoagulants (warfarin, phenindione) — consider increased monitoring of international normalized ratio (INR) and adjust the dose accordingly.
• Posaconazole and voriconazole — concentrations of antifungal is greatly decreased. If concurrent use is unavoidable, monitor for decreased efficacy and consider increasing the dose of the azole (although this may not resolve the issue). 
• Probenecid — concomitant administration may result in increased levels of flucloxacillin.
• Live cholera vaccine — efficacy of the vaccine may be reduced. Avoid flucloxacillin from 14 days before to 10 days after receiving live cholera vaccine.
• Live typhoid vaccine — immune response to vaccine may be reduced. Avoid flucloxacillin from 3 days before to 3 days after receiving live typhoid vaccine.
• Paracetamol — caution is advised when flucloxacillin is used with paracetamol, as concurrent intake has been associated with high anion gap metabolic acidosis.

[EMC, 2025a; EMC, 2025d; Preston, 2026]