Clarithromycin
6-O-Methylerythromycin
Also known as: Biaxin XL · Klacid · Klaricid · Maclar · Prevpak (combination) · 6O-Methylerythromycin · TE-031 · A-56268
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Dosing by species
🌎 NA — North America🌍 EU — Europe
Dogs
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Treatment of severe or refractory cases of canine leproid granuloma syndrome | 15-25 mg/kg total daily dose PO given divided q8-12h | PO | q8-12h | 4-8 weeks until lesions are substantially reduced or resolved | 🌎 NA |
| Susceptible infections | 2.5-10 mg/kg PO twice daily | PO | q12h | — | 🌎 NA |
| Susceptible infections | 5-10 mg/kg PO q12h | PO | q12h | — | 🌎 NA |
- Treatment of severe or refractory cases of canine leproid granuloma syndrome: Used in combination with rifampin 10-15 mg/kg PO once daily.
Cats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Treatment of feline leprosy | 62.5 mg per cat q12h | PO | q12h | — | 🌎 NA |
| Treatment of Nocardia (N. nova) infections | 62.5-125 mg (total dose per cat) PO twice daily | PO | q12h | — | 🌎 NA |
| Treatment of H. pylori infections | 7.5 mg/kg PO twice daily | PO | q12h | 14 days | 🌎 NA |
| Treatment of M. tuberculosis-bovis variant infections | 5-10 mg/kg PO q12h | PO | q12h | At least 2 months, then maintenance for 4 months | 🌎 NA |
| Susceptible infections | 7.5 mg/kg PO q12h | PO | q12h | — | 🌎 NA |
- Treatment of feline leprosy: Used in a regimen of 2 or 3 drugs including clofazimine and/or rifampin.
- Treatment of Nocardia (N. nova) infections: Combination therapy with amoxicillin and/or doxycycline.
- Treatment of H. pylori infections: Combination therapy with metronidazole and amoxicillin.
- Treatment of M. tuberculosis-bovis variant infections: Used with rifampin and enrofloxacin.
Ferrets
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Treatment of Helicobacter mustelae infections | 12.5 mg/kg PO q12h | PO | q12h | 14 days | 🌎 NA |
| Treatment of Helicobacter mustelae infections | 12.5-50 mg/kg q8-24h | PO | q8-24h | — | 🌎 NA |
- Treatment of Helicobacter mustelae infections: With ranitidine bismuth citrate. Same regimen given q8h is also published.
- Treatment of Helicobacter mustelae infections: With omeprazole at 0.7 mg/kg PO once daily.
Horses
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Treatment of Rhodococcus equi infection in foals | 7.5 mg/kg PO q12h | PO | q12h | — | 🌎 NA |
| Treatment of Rhodococcus equi infection in foals | 7.5 mg/kg PO q12h | PO | q12h | — | 🌎 NA |
- Treatment of Rhodococcus equi infection in foals: In combination with rifampin at 5 mg/kg PO q12h or 10 mg/kg PO q24h.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Clarithromycin is a semi-synthetic macrolide antibiotic closely related to erythromycin. It is structurally modified via the methylation of position 6 in the lactone ring, which confers improved acid stability, better oral bioavailability, and a broader spectrum of activity compared to its parent compound.
Key Clinical Features:
- Spectrum of Activity: Similar to erythromycin but highly effective against atypical mycobacteria (e.g., Mycobacterium avium complex), Helicobacter spp., and Rhodococcus equi.
- Clinical Utility: Primarily used in small animals for atypical mycobacterial infections (like feline leprosy or canine leproid granuloma) and Helicobacter eradication protocols. In equine medicine, it is a cornerstone treatment for Rhodococcus equi pneumonia in foals.
- Tolerability: Generally better tolerated than erythromycin, with fewer gastrointestinal side effects, as it has less prokinetic (motilin-receptor agonist) activity.
Clinical Pearl: Clarithromycin is a potent inhibitor of the cytochrome P450 3A (CYP3A) enzyme system. Concurrent use with other drugs metabolized by this pathway requires careful review to avoid toxicity.
Mechanism of action
Clarithromycin is typically bacteriostatic, though it can be bactericidal at high concentrations against highly susceptible organisms.
- Mechanism: It penetrates the bacterial cell wall and reversibly binds to the P site of the 50S ribosomal subunit.
- Pathway: Binding → Inhibition of RNA-dependent protein synthesis (blocks transpeptidation and translocation) → Suppression of bacterial growth.
- Post-Antibiotic Effect (PAE): Macrolides generally exhibit a prolonged PAE against Gram-positive pathogens, allowing for sustained efficacy even when plasma levels drop below the MIC.
Safety & warnings
Contraindications
- Known hypersensitivity to clarithromycin or other macrolide antibiotics (e.g., erythromycin, azithromycin)
- Concurrent use with cisapride (due to risk of fatal cardiac arrhythmias)
Adverse effects
- Gastrointestinal disturbances (nausea, vomiting, anorexia, diarrhea)
- Pinnal or generalized erythema (specifically noted in cats)
- Transient, mild BUN elevation
- Prolonged QT interval / torsades de pointes (rare)
- Hepatotoxicity (rare)
- Thrombocytopenia (rare)
- Pseudomembranous colitis secondary to Clostridium difficile (reported in humans)
Precautions
Pregnancy & Lactation: FDA Category C. High doses in animal studies showed some teratogenic effects (cleft palate, fetal growth retardation). Use only if benefits outweigh risks. Excreted into milk, though unlikely to be clinically significant. Hepatic/Renal Impairment: Use with caution; dose adjustments may be necessary in severe renal or hepatic dysfunction. Drug Interactions: Potent CYP3A inhibitor. Always review concurrent medications before prescribing.
Drug interactions
Clarithromycin inhibits cisapride metabolism; concurrent use is contraindicated due to risk of severe cardiac arrhythmias.
May increase clarithromycin serum levels.
Clarithromycin may increase serum levels of digoxin.
Concurrent use can increase the plasma levels of both drugs.
May potentiate the effects of oral anticoagulant drugs.
Clarithromycin may decrease serum concentrations of zidovudine.
Clarithromycin inhibits CYP3A, potentially increasing plasma concentrations and toxicity of these drugs. Therapeutic monitoring or dose reduction may be required.
Increased levels and risk of prolonged QT interval.
Increased levels and risk of prolonged QT interval.
Monitoring
- Clinical efficacy (resolution of infection)
- Gastrointestinal adverse effects
- Signs of erythema (especially in cats)
- Potential drug interactions if on concurrent medications
Pharmacokinetics
Half-life
Absorption
In dogs, bioavailability ranges from 60-83%, with higher values obtained in fasted animals. In foals, it is well absorbed after intragastric administration with peak serum concentrations at ~1.5 hours.
Distribution
Widely distributed into tissues; penetrates susceptible bacterial cell walls effectively. Achieves high intracellular concentrations.
Metabolism
Undergoes hepatic metabolism. It is a known inhibitor of the CYP3A subfamily of the cytochrome P450 enzyme system.
Elimination
Excreted via urine and feces. Excreted into the milk of lactating animals.
Overdose
Overdoses of clarithromycin are generally not life-threatening and primarily result in gastrointestinal distress (vomiting, diarrhea, cramping).
- Treatment: For recent, large ingestions, administration of activated charcoal with a cathartic may help remove unabsorbed drug.
- Note: Forced diuresis, peritoneal dialysis, or hemodialysis are not effective in enhancing the elimination of clarithromycin from the body.
Available products
Formulations
- Oral tablets (regular and film-coated)
- Extended-release oral tablets
- Granules for oral suspension
Human-labeled
- Clarithromycin Regular & Film-coated Oral Tablets: 250 mg & 500 mg
- Clarithromycin Extended-release Tablets: 500 mg
- Clarithromycin Granules for Oral Suspension: 125 mg/5 mL & 250 mg/5 mL (after reconstitution)
- Pre-packaged combination (Prevpak) containing lansoprazole, amoxicillin, and clarithromycin
Regulatory status
No regulatory data for: 🇺🇸 US · 🇪🇺 EU · 🇬🇧 UK · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Conventional 250 mg tablets: Protect from light, store in well-closed containers at 15-30°C (59-86°F). Conventional/ER 500 mg tablets: Store at controlled room temperature (20-25°C; 68-77°F). Granules for suspension: Store unmixed granules at 15-30°C. After reconstitution, store at room temperature (DO NOT refrigerate) and discard any unused drug after 14 days.
Client information
Clarithromycin is an antibiotic used to treat specific types of bacterial infections.
- Administration: You can give this medication with or without food. If your pet vomits after taking it on an empty stomach, try giving future doses with a small treat or meal.
- Liquid Suspension: If you are using the liquid form, do not refrigerate it. Keep it at room temperature. Shake well before each use, and throw away any leftover liquid after 14 days.
- Drug Interactions: Clarithromycin can interact with many other medications. Never give your pet any new medications, supplements, or over-the-counter drugs without checking with your veterinarian first.
- Side Effects: Watch for vomiting, diarrhea, or loss of appetite. In cats, you might occasionally notice redness of the skin or ears. Contact your vet if these occur.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.