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Drug Reference

clarithromycin

Macrolide antibiotics· Brands: Klacid, Biaxin, Klaricid, ClaritekIVPO

Mechanism of action
Clarithromycin is a macrolide antibiotic that binds to the 50S subunit of bacterial ribosomes, inhibiting protein synthesis. It is generally bacteriostatic but may be bactericidal against some pathogens. It has activity against a range of Gram-positive bacteria, some Gram-negative organisms, and atypical pathogens including Mycoplasma, Legionella, and Chlamydia. It is also used for Helicobacter pylori eradication.
Pharmacokinetics
Clarithromycin is well absorbed after oral administration, with a bioavailability of approximately 50%. It is extensively metabolised in the liver by CYP3A4, forming an active metabolite, 14-hydroxyclarithromycin. The half-life is about 3 to 7 hours, and it achieves high tissue concentrations, particularly in respiratory secretions. Excretion is mainly via the urine and bile.
Indications & dosing

Community-acquired pneumonia

Treat for 7 to 14 days.

  • adult · PO: 500 mg every 12 hours · Treat for 7 to 14 days.

Acute exacerbation of chronic bronchitis

Treat for 7 to 14 days.

  • adult · PO: 500 mg every 12 hours · Treat for 7 to 14 days.

Pharyngitis/tonsillitis

For 10 days. Penicillin is preferred if susceptible.

  • adult · PO: 250 mg every 12 hours · For 10 days. Penicillin is preferred if susceptible.

Helicobacter pylori eradication

Used in combination with a PPI and another antibiotic, e.g., amoxicillin, for 7 to 14 days.

  • adult · PO: 500 mg every 12 hours · Used in combination with a PPI and another antibiotic, e.g., amoxicillin, for 7 to 14 days.

Skin and soft tissue infections

Use 500 mg for severe infections, 250 mg for mild to moderate.

  • adult · PO: 250–500 mg every 12 hours · Use 500 mg for severe infections, 250 mg for mild to moderate.

Mycobacterium avium complex (MAC) prophylaxis in HIV

For prevention or treatment of disseminated MAC disease in advanced HIV infection.

  • adult · PO: 500 mg every 12 hours · For prevention or treatment of disseminated MAC disease in advanced HIV infection.
Contraindications & precautions
  • Hypersensitivity to clarithromycin or other macrolides · Cross-sensitivity may occur
  • Concomitant use with terfenadine, astemizole, cisapride, or pimozide · Risk of QT prolongation and torsades de pointes
  • Concomitant use with ergot alkaloids (e.g., ergotamine, dihydroergotamine) · Risk of ergotism
  • History of QT interval prolongation or ventricular arrhythmias · Use only if no alternative, with close monitoring
  • Severe hepatic impairment · Avoid if possible; consider alternative antibiotic
  • Use caution in hepatic impairment; reduce dose or avoid in severe dysfunction.
  • Adjust dose in severe renal impairment (creatinine clearance <30 mL/min).
  • Avoid concomitant simvastatin or lovastatin due to risk of rhabdomyolysis; if required, use a low dose of another statin or temporarily discontinue.
  • Monitor for QT prolongation in patients with electrolyte disturbances, bradycardia, or concurrent QT-prolonging drugs.
  • Caution in myasthenia gravis; macrolides can worsen neuromuscular blockade.
  • Discontinue if severe diarrhoea develops; evaluate for antibiotic-associated colitis.
Adverse effects
  • Nausea
  • Diarrhoea
  • Dysgeusia (taste disturbance)
  • Abdominal pain
  • Headache
  • QT prolongation / ventricular arrhythmia (e.g., torsades de pointes)serious
  • Hepatotoxicity (e.g., cholestatic jaundice, hepatitis)serious
  • Pseudomembranous colitis (Clostridium difficile-associated diarrhoea)serious
  • Anaphylaxisserious
  • Stevens-Johnson syndrome / toxic epidermal necrolysisserious
Interactions
  • dabigatranmajorAvoid co-prescription. If combination is essential, consider reducing the dabigatran dose and monitor closely for signs of bleeding; alternatively, choose an antibiotic that does not inhibit P-gp (e.g., azithromycin or doxycycline). Consult local guidelines for dabigatran dose adjustment in renal impairment.
  • amiodaronecontraindicatedCoadministration is contraindicated. Avoid the combination and consider alternative antibacterial therapy. If coadministration is absolutely necessary, it should be done in a hospital setting with continuous ECG monitoring and immediate availability of resuscitation facilities, but ideally the combination should not be used.
  • cyclosporinemajorAvoid concomitant use of clarithromycin and cyclosporine if possible. If co-administration is considered necessary, reduce the cyclosporine dose empirically by approximately 50% and closely monitor cyclosporine trough levels, renal function, and blood pressure. Measure cyclosporine concentrations before starting clarithromycin, then twice weekly during co-administration, and after discontinuing clarithromycin. Adjust the cyclosporine dose to maintain therapeutic levels. Consider alternative macrolides with less CYP3A4 inhibitory activity, such as azithromycin, if appropriate.
  • tacrolimusmajorAvoid co-prescription where possible. If unavoidable, consider a non-interacting macrolide (e.g., azithromycin) or another antibiotic. If the combination is necessary, reduce the tacrolimus dose (often by 50% or more), monitor trough levels frequently (e.g., every 2-3 days) and adjust based on levels. Monitor renal function, blood glucose, and signs of neurotoxicity.
  • simvastatincontraindicatedAvoid co-prescription of clarithromycin and simvastatin. If an antibiotic is required, consider an alternative macrolide (e.g., azithromycin) or another antibiotic that does not inhibit CYP3A4. If a statin is required, consider a statin not metabolised by CYP3A4, such as pravastatin or rosuvastatin. If temporary combination is deemed absolutely necessary, simvastatin should be withheld during clarithromycin therapy; however, this approach is rarely acceptable given the contraindication.
  • warfarinmajorAvoid co-prescription if possible. If no suitable alternative antibiotic is available, closely monitor the INR, particularly during the first week of concurrent therapy, and adjust the warfarin dose as necessary. Continue monitoring for a few days after stopping clarithromycin.
  • apixabanmajorAvoid co-prescription if possible. If combined use is essential, reduce the apixaban dose (for example, from 5 mg twice daily to 2.5 mg twice daily) and monitor the patient closely for signs of bleeding. Do not use this combination in patients already taking apixaban 2.5 mg twice daily. Consider alternative antibiotics that are not strong CYP3A4/P-gp inhibitors.
  • digoxinmajorAvoid co-prescription when possible. If use is necessary, consider reducing the digoxin dose and closely monitoring serum digoxin concentrations and renal function before and during therapy. Monitor the patient for signs of digoxin toxicity, including heart rate and rhythm. Consider alternative antibiotics that do not inhibit P-glycoprotein (e.g., azithromycin has a less pronounced effect) where appropriate.
  • atorvastatinmajorAvoid co-prescribing atorvastatin with clarithromycin where alternatives exist. If concurrent use is necessary, use the lowest effective atorvastatin dose (e.g., 10 to 20 mg daily) and monitor for muscle symptoms and creatine kinase levels regularly. Consider temporary suspension of atorvastatin during clarithromycin therapy if possible.
  • theophyllinemajorAvoid concomitant use if possible. If co-administration is necessary, monitor theophylline serum concentrations closely and adjust the dose accordingly. Patients should be observed for signs of theophylline toxicity, such as nausea, palpitations, and tremors.
  • carbamazepinemajorAvoid coadministration where possible. If combined therapy is necessary, monitor carbamazepine plasma concentrations at baseline and after initiation of clarithromycin, and adjust the carbamazepine dose accordingly. Monitor the patient for clinical signs of toxicity. Consider alternative antibiotics with less CYP3A4 inhibition, such as azithromycin.
  • rivaroxabanmajorAvoid co-prescription of rivaroxaban and clarithromycin. If alternative antibiotics are not suitable, monitor patients closely for signs of bleeding, and consider a temporary reduction in rivaroxaban dose or switching to a less interacting antibiotic such as azithromycin or doxycycline. Assess renal function and reassess anticoagulant requirements during therapy.
  • edoxabanmajorAvoid coadministration unless the benefit clearly outweighs the risk. If unavoidable, consider reducing the edoxaban dose by half (for example, from 60 mg to 30 mg once daily). Monitor the patient closely for signs of bleeding, and assess renal function at baseline and periodically. Consider an alternative antibiotic with minimal P-gp inhibition, such as azithromycin, if clinically appropriate. Instruct the patient to seek urgent medical attention if they develop unusual bleeding.
  • colchicinemajorAvoid co-prescription whenever possible, especially in patients with renal or hepatic impairment. If a macrolide is needed, consider azithromycin, which does not significantly inhibit CYP3A4. If co-administration is unavoidable in a patient with normal renal and hepatic function, reduce the colchicine dose (e.g., to 0.6 mg once daily) and monitor closely for signs of toxicity, including blood counts and renal function.
Renal & hepatic adjustment
  • eGFR 0–29: Reduce dose by 50% or double the dosing interval; monitor renal function closely.
  • eGFR 30–59: No dose adjustment required, but use caution and monitor for adverse effects.
  • Hepatic impairment (mild): no dose adjustment required
  • Hepatic impairment (moderate): no dose adjustment required, but monitor liver function
  • Hepatic impairment (severe): use with caution; consider reducing dose or using alternative, especially if combined with renal impairment (avoid)
Monitoring, pregnancy & toxicity
  • Liver function tests · Baseline and periodically during therapy, especially in patients with hepatic impairment or on long-term treatment
  • ECG (QT interval) · In patients at risk of QT prolongation, such as those with electrolyte imbalance or taking other QT-prolonging drugs
  • Renal function · Before and during therapy in patients with renal impairment
  • Signs of superinfection or overgrowth · Throughout therapy
  • Drug interactions (e.g., with statins, warfarin) · Before and during therapy
  • Pregnancy: Avoid during pregnancy, especially in the first trimester, unless the benefits clearly outweigh the risks; alternative antibiotics are preferred.
  • Toxicity: QT prolongation and cardiac arrhythmias (e.g., torsades de pointes) · Discontinue drug, monitor ECG, correct electrolyte abnormalities, provide supportive care
  • Toxicity: Gastrointestinal disturbances (nausea, vomiting, diarrhoea) · Supportive care, rehydration, consider dose reduction or switching to another antibiotic
  • Toxicity: Hepatotoxicity (elevated liver enzymes, hepatitis) · Discontinue drug, monitor liver function, supportive care
  • Toxicity: Allergic reactions (rash, anaphylaxis) · Discontinue drug, symptomatic treatment, including antihistamines or adrenaline if necessary
Clinical notes
Clarithromycin is indicated for respiratory tract infections, skin and soft tissue infections, and as part of combination therapy for Helicobacter pylori. It may cause gastrointestinal side effects and is associated with QT prolongation, so caution is required with other drugs that prolong the QT interval. It is a potent CYP3A4 inhibitor, leading to significant interactions with statins, warfarin, and some antiepileptics. Dose adjustment may be necessary in renal impairment.

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BNF; local formulary