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. |
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 | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Inhibits CYP3A4 increasing levels of many drugs (eg statins carbamazepine) May cause QT prolongation and subsequent arrhythmias.
| Breastfeeding | Clarithromycin excreted into breast milk (M/P ratio ~0.5-2.0). Infant exposure via milk is low (<2% maternal dose). Consider risk of infant diarrhea, rash, or altered gut flora. Use caution in breastfeeding, especially in infants <2 months. |
| 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. |
■ FDA Black Box Warning
None
| Common Effects | Diarrhea |
| Serious Effects |
["Hypersensitivity to clarithromycin, erythromycin, or any macrolide antibiotic","Concurrent use with ergotamine or dihydroergotamine (risk of ergot toxicity)","Concurrent use with HMG-CoA reductase inhibitors (statins) metabolized by CYP3A4 (e.g., simvastatin, lovastatin) due to risk of rhabdomyolysis","Concurrent use with ranolazine, lomitapide, or certain antiarrhythmics (e.g., disopyramide, quinidine, dofetilide, sotalol) due to risk of QT prolongation","Cholestatic jaundice or hepatic impairment with prior clarithromycin use","History of QTc interval prolongation or ventricular arrhythmias including torsades de pointes"]
| 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"] |
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| 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. |