Clarithromycin
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.
Mecanismo: 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.
Dosificación por especie
- Treatment of feline leprosy · 62.5 mg per cat q12h · PO · q12h · Used in a regimen of 2 or 3 drugs including clofazimine and/or rifampin.
- Treatment of Nocardia (N. nova) infections · 62.5-125 mg (total dose per cat) PO twice daily · PO · q12h · Combination therapy with amoxicillin and/or doxycycline.
- Treatment of H. pylori infections · 7.5 mg/kg PO twice daily · PO · q12h · 14 days · Combination therapy with metronidazole and amoxicillin.
- Treatment of M. tuberculosis-bovis variant infections · 5-10 mg/kg PO q12h · PO · q12h · At least 2 months, then maintenance for 4 months · Used with rifampin and enrofloxacin.
- Susceptible infections · 7.5 mg/kg PO q12h · PO · q12h
- Treatment of Helicobacter mustelae infections · 12.5 mg/kg PO q12h · PO · q12h · 14 days · With ranitidine bismuth citrate. Same regimen given q8h is also published.
- Treatment of Helicobacter mustelae infections · 12.5-50 mg/kg q8-24h · PO · q8-24h · With omeprazole at 0.7 mg/kg PO once daily.
- Treatment of Rhodococcus equi infection in foals · 7.5 mg/kg PO q12h · PO · q12h
- Treatment of Rhodococcus equi infection in foals · 7.5 mg/kg PO q12h · PO · q12h · In combination with rifampin at 5 mg/kg PO q12h or 10 mg/kg PO q24h.
Vías de administración
Contraindicaciones
- Known hypersensitivity to clarithromycin or other macrolide antibiotics (e.g., erythromycin, azithromycin)
- Concurrent use with cisapride (due to risk of fatal cardiac arrhythmias)
Efectos adversos
- 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)
Interacciones farmacológicas
- Cisapride · Clarithromycin inhibits cisapride metabolism; concurrent use is contraindicated due to risk of severe cardiac arrhythmias.
- Fluconazole · May increase clarithromycin serum levels.
- Digoxin · Clarithromycin may increase serum levels of digoxin.
- Omeprazole · Concurrent use can increase the plasma levels of both drugs.
- Warfarin · May potentiate the effects of oral anticoagulant drugs.
- Zidovudine · Clarithromycin may decrease serum concentrations of zidovudine.
- CYP3A Substrates (Alfentanil, Bromocriptine, Buspirone, Carbamazepine, Methylprednisolone, Midazolam, Alprazolam, Triazolam, Rifabutin, Tacrolimus, Theophylline) · Clarithromycin inhibits CYP3A, potentially increasing plasma concentrations and toxicity of these drugs. Therapeutic monitoring or dose reduction may be required.
- Disopyramide · Increased levels and risk of prolonged QT interval.
- Quinidine · Increased levels and risk of prolonged QT interval.
Monitoreo
- Clinical efficacy (resolution of infection)
- Gastrointestinal adverse effects
- Signs of erythema (especially in cats)
- Potential drug interactions if on concurrent medications
Sobredosis
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.
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