クラリスロマイシン
クラリスロマイシンは、エリスロマイシンに関連する半合成の**マクロライド系抗生物質**です。ラクトン環の6位がメチル化されることで構造が修飾されており、親化合物と比較して酸に対する安定性が向上し、経口バイオアベイラビリティが高く、抗菌スペクトルが広くなっています。 **主な臨床的特徴:** * **抗菌スペクトル:** エリスロマイシンと似ていますが、**非定型抗酸菌**（例：マイコバクテリウム・アビウム・コンプレックス）、*ヘリコバクター*属、および*ロドコッカス・エクイ*に対して非常に有効です。 * **臨床的有用性:** 小動物では主に非定型抗酸菌感染症（猫ハンセン病や犬の類ハンセン病肉芽腫など）や*ヘリコバクター*除菌プロトコルに使用されます。馬の医療では、子馬の*ロドコッカス・エクイ*肺炎の主要な治療薬です。 * **忍容性:** エリスロマイシンよりも一般的に忍容性が高く、消化管の副作用が少ない（モチリン受容体作動作用による消化管運動促進作用が弱いため）のが特徴です。 > **臨床上のポイント:** クラリスロマイシンはシトクロムP450 3A（CYP3A）酵素系の強力な阻害剤です。この経路で代謝される他の薬剤と併用する場合は、毒性を避けるために慎重な確認が必要です。
作用機序: 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.
動物種別の用量
- 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.
投与経路
禁忌
- Known hypersensitivity to clarithromycin or other macrolide antibiotics (e.g., erythromycin, azithromycin)
- Concurrent use with cisapride (due to risk of fatal cardiac arrhythmias)
有害事象
- 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)
薬物相互作用
- 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.
モニタリング
- Clinical efficacy (resolution of infection)
- Gastrointestinal adverse effects
- Signs of erythema (especially in cats)
- Potential drug interactions if on concurrent medications
過量投与
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.
VetSheet の薬剤リファレンスは、獣医療従事者向けの臨床意思決定支援を目的としており、専門的判断やメーカーの最新添付文書に代わるものではありません。