克拉黴素
克拉黴素（Clarithromycin）是一種半合成的**巨環類抗生素**，與紅黴素（Erythromycin）結構相似。它透過內酯環第6位的甲基化進行結構修飾，這使其比母體化合物具有更好的胃酸穩定性、更高的口服生物利用度以及更廣的抗菌譜。 **主要臨床特徵：** * **抗菌譜：** 與紅黴素相似，但對**非典型分枝桿菌**（例如禽分枝桿菌複合群）、*幽門螺旋桿菌*及*馬紅球菌*具有極佳的療效。 * **臨床應用：** 在小動物醫學中，主要用於治療非典型分枝桿菌感染（如貓痲瘋或犬痲瘋樣肉芽腫）以及*幽門螺旋桿菌*的根除療程。在馬科醫學中，它是治療幼駒*馬紅球菌*肺炎的核心藥物。 * **耐受性：** 通常比紅黴素具有更好的耐受性，胃腸道副作用較少（因為其促進胃腸蠕動的胃動素受體激動作用較弱）。 > **臨床要點：** 克拉黴素是細胞色素 P450 3A (CYP3A) 酵素系統的強效抑制劑。若與其他經此途徑代謝的藥物併用，必須謹慎評估以避免毒性反應。
作用機制: 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.
各物種劑量
- 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.
給藥途徑
禁忌症
- Known hypersensitivity to clarithromycin or other macrolide antibiotics (e.g., erythromycin, azithromycin)
- Concurrent use with cisapride (due to risk of fatal cardiac arrhythmias)
不良反應
- 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)
藥物相互作用
- 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.
監測
- Clinical efficacy (resolution of infection)
- Gastrointestinal adverse effects
- Signs of erythema (especially in cats)
- Potential drug interactions if on concurrent medications
過量
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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