CLARITHROMYCIN
Clinical safety rating: caution
Animal studies have proved adverse effects but may be safe for humans
Clarithromycin inhibits bacterial protein synthesis by binding to the 50S ribosomal subunit, specifically to the 23S rRNA component, blocking peptide chain elongation and exerting bacteriostatic or bactericidal effects depending on concentration and organism.
| Metabolism | Primarily hepatic via cytochrome P450 3A (CYP3A) isoenzymes; undergoes oxidative N-demethylation and hydroxylation to produce 14-hydroxyclarithromycin (active metabolite). |
| Excretion | Renal: approximately 30-40% unchanged; biliary/fecal: approximately 40-50% as metabolites; total renal clearance accounts for about 30-40% of dose; hepatic metabolism contributes to elimination; dose adjustment required in severe renal impairment (CrCl <30 mL/min). |
| Half-life | Terminal elimination half-life: 5-7 hours in adults with normal renal function; prolonged to 8-12 hours in moderate to severe renal impairment; clinical context: allows twice-daily dosing; active metabolite (14-hydroxyclarithromycin) half-life similar. |
| Protein binding | Approximately 65-70% bound, primarily to albumin; binding is concentration-dependent, decreasing at high concentrations. |
| Volume of Distribution | Vd: 3-4 L/kg (approximately 200-300 L in adults); extensive tissue distribution; accumulates in tissues (e.g., lung, tonsils, nasal mucosa) to levels 10-100 times serum concentrations; crosses placenta and enters breast milk. |
| Bioavailability | Oral immediate-release: approximately 50-55% due to first-pass metabolism; food may slightly increase bioavailability; oral suspension: similar to tablets; IV: 100% (not applicable). |
| Onset of Action | Oral: 1-2 hours to achieve therapeutic plasma concentrations; time to clinical symptom relief (e.g., fever reduction in respiratory infections) typically 24-72 hours; IV: immediate upon infusion completion, therapeutic levels achieved within 30 minutes. |
| Duration of Action | Recommended dosing interval: every 12 hours; clinical duration of antimicrobial effect covers 12 hours; sustained release formulation (500 mg once daily) provides 24-hour coverage; post-antibiotic effect of 1-4 hours against susceptible organisms. |
| Molecular Weight | 747.96 |
250-500 mg orally twice daily for 7-14 days; for MAC infection: 500 mg twice daily.
| Dosage form | TABLET, EXTENDED RELEASE |
| Renal impairment | CrCl 30-60 mL/min: reduce dose by 50% or increase dosing interval to once daily; CrCl <30 mL/min: 250 mg once daily or 500 mg every 48 hours. |
| Liver impairment | Child-Pugh A/B: no adjustment; Child-Pugh C: avoid use due to potential accumulation. |
| Pediatric use | 7.5 mg/kg orally twice daily (max 500 mg/dose) for 7-10 days; for MAC: 7.5-15 mg/kg twice daily (max 500 mg/dose). |
| Geriatric use | No specific geriatric dose adjustment; use caution in renal impairment and monitor for QT prolongation and gastrointestinal effects. |
| 1st trimester | Limited human data; animal studies show embryotoxicity at high doses. Use only if benefit outweighs risk. Consider alternative macrolide such as azithromycin. |
| 2nd trimester | Generally considered safe based on observational data; no increased risk of major malformations. Use if indicated. |
| 3rd trimester | Safe to use; no known adverse fetal effects near term. Crosses placenta but no significant neonatal toxicity. |
Clinical note
Inhibits CYP3A4 increasing levels of many drugs (eg statins carbamazepine) May cause QT prolongation and subsequent arrhythmias.
| Placental transfer | Crosses placenta; fetal concentrations approximately 50% of maternal serum concentrations. |
| Breastfeeding | Clarithromycin is excreted into breast milk in small amounts (estimated relative infant dose <1% of maternal weight-adjusted dose). No adverse effects reported in nursing infants. Use with caution in infants with hepatic or renal impairment. Monitor for diarrhea or rash. |
■ FDA Black Box Warning
None
| Common Effects | Diarrhea |
| Serious Effects |
Known hypersensitivity to clarithromycin or any macrolide antibioticConcurrent use with ergotamine or dihydroergotamine (risk of ergotism)Concurrent use with HMG-CoA reductase inhibitors that are extensively metabolized by CYP3A4 (e.g., atorvastatin, lovastatin, simvastatin) due to increased risk of rhabdomyolysisConcurrent use with pimozide (increased risk of arrhythmias)Combination with cisapride (QT prolongation risk)History of cholestatic jaundice or hepatic dysfunction with previous clarithromycin useConcurrent use with ticagrelor or ranolazine
| Precautions | Increased risk of cardiac arrhythmias, including QT prolongation and torsades de pointes, especially in patients with pre-existing cardiac conditions, electrolyte abnormalities, or concomitant use of other QT-prolonging drugs, Exacerbation of myasthenia gravis symptoms, Severe acute hypersensitivity reactions including Stevens-Johnson syndrome and toxic epidermal necrolysis, Hepatic dysfunction, including hepatocellular and cholestatic hepatitis, which may be severe and potentially fatal, Increased mortality risk in patients with coronary artery disease (based on some observational studies), Potential for antibiotic-associated colitis due to Clostridioides difficile overgrowth, Drug interactions due to CYP3A4 inhibition, including increased plasma concentrations of statins, warfarin, colchicine, ergot alkaloids, benzodiazepines, and calcium channel blockers |
Loading safety data…
| Lactation Rating | L1 (Safe, compatible with breastfeeding) |
| Teratogenic Risk | First trimester: increased risk of miscarriage and cardiovascular malformations (odds ratio ~1.5-2.0). Second/third trimester: no specific major teratogenicity; use only if benefit outweighs risk due to potential for maternal hepatotoxicity. |
| Fetal Monitoring | Monitor maternal liver function tests (LFTs) and renal function. For fetus, consider serial ultrasounds if first trimester exposure to assess for cardiac anomalies. Monitor for maternal QT prolongation if risk factors present. |
| Fertility Effects | No known adverse effects on fertility in animal studies. Limited human data; no evidence of impaired fertility or reproductive function. |
| Food/Dietary | Avoid concurrent intake of grapefruit or grapefruit juice, as it may increase clarithromycin serum concentrations via CYP3A4 inhibition. High-fat meals may modestly increase absorption. |
| Clinical Pearls | Clarithromycin is a macrolide antibiotic with a 14-membered lactone ring; it inhibits bacterial protein synthesis by binding to the 50S ribosomal subunit. It has a prolonged half-life and excellent tissue penetration. Due to its potent CYP3A4 inhibition, it significantly increases levels of statins, warfarin, and other CYP3A4 substrates, which can lead to rhabdomyolysis or bleeding. It is also associated with QTc prolongation; avoid in patients with electrolyte abnormalities, bradycardia, or concurrent QTc-prolonging drugs. Double-check drug interactions before prescribing. |
| Patient Advice | Take clarithromycin exactly as prescribed, with or without food. · Complete the full course even if you feel better. · Do not take with pimozide, ergot alkaloids, or cisapride due to serious interactions. · Avoid grapefruit and grapefruit juice during treatment. · Contact your doctor immediately if you experience chest pain, palpitations, or fainting (signs of QTc prolongation). · Report any muscle pain, weakness, or dark urine (possible rhabdomyolysis). · Use effective contraception as clarithromycin may reduce efficacy of hormonal contraceptives. |