テトラサイクリン
テトラサイクリンは、プロトタイプとなる短時間作用型の**テトラサイクリン系抗生物質**です。歴史的には広域スペクトル抗菌薬として使用されてきましたが、細菌の耐性増加によりその臨床的役割は変化しています。 現代の獣医療において： * **小動物臨床**：感染症に対しては、組織移行性が良く投与頻度が少ないドキシサイクリンが一般的に好まれます。しかし、テトラサイクリンは**ナイアシンアミド**と併用され、その免疫調節作用を利用して免疫介在性皮膚疾患（円板状エリテマトーデス、天疱瘡など）の治療に頻繁に使用されます。 * **大動物臨床**：通常、オキシテトラサイクリンが好まれます。 **臨床のポイント**： * *マイコプラズマ*、*リケッチア*、スピロヘータ（ライム病など）、*クラミジア*などの非定型病原体に対しては依然として有効です。 * 顕著な**抗炎症および免疫調節作用**を持ち、獣医皮膚科において価値があります。
作用機序: Tetracycline is a **time-dependent, bacteriostatic antibiotic**. * **Antimicrobial Action**: Reversibly binds to the **30S ribosomal subunit** of susceptible organisms → prevents binding of aminoacyl transfer-RNA to the ribosome → inhibits bacterial protein synthesis. It may also bind to the 50S subunit and alter cytoplasmic membrane permeability. * **Immunomodulatory/Anti-inflammatory Action**: Suppresses antibody production and neutrophil chemotaxis. Inhibits key inflammatory mediators including **lipases, collagenases, prostaglandin synthesis**, and the activation of complement component 3.
動物種別の用量
- Susceptible infections · 11 mg/kg, PO twice daily · PO · q12h · up to 5 days
- Soft tissue infections · 20 mg/kg PO q8h · PO · q8h · 21 days
- Hemotropic mycoplasmosis · 10-25 mg/kg PO q8-12h · PO · q8-12h · 21 days
- Bacteremia, systemic infections · 7 mg/kg IV , IM q12h · IV/IM · q12h · as long as necessary
- Rickettsial diseases · 16 mg/kg, PO three times daily · PO · q8h · 21 days
- Susceptible infections · 20 mg/kg PO q8-12h · PO · q8-12h · May give with food if GI upset occurs; avoid or reduce dose in animals with renal or severe liver failure; avoid in young, pregnant or breeding animals
- Susceptible infections · 22-33 mg/kg PO q8h · PO · q8h
- Susceptible infections · 25 mg/kg PO 2-3 times daily · PO · q8-12h
- Susceptible infections in calves · 11 mg/kg orally · PO · Not specified
- Susceptible infections in calves · 11 mg/kg, PO twice daily · PO · q12h · up to 5 days
投与経路
禁忌
- Hypersensitivity to tetracyclines
- Pregnancy (last half) - retards fetal skeletal development and discolors teeth
- Young, growing animals (unless benefits outweigh risks)
有害事象
- Gastrointestinal distress (nausea, vomiting, anorexia, diarrhea)
- Discoloration of developing teeth and bones (yellow/brown/gray)
- Delayed bone growth and healing in young animals
- Superinfections (bacterial or fungal overgrowth)
- Photosensitivity
- Urolith formation (with long-term use in dogs)
- Hepatotoxicity and blood dyscrasias (rare)
- Cats: Colic, fever, hair loss, depression (poorly tolerated)
- Horses: Severe diarrhea (especially if stressed)
- Ruminants: Ruminal microflora depression and stasis (high oral doses)
- Injection site reactions (IM): Local necrosis and yellow staining
薬物相互作用
- Atovaquone · Tetracyclines may decrease atovaquone levels.
- Beta-lactam or Aminoglycoside Antibiotics · Theoretical antagonism of bactericidal activity, though clinical significance is doubtful.
- Digoxin · May increase bioavailability of digoxin, potentially causing toxicity that persists for months.
- Divalent or Trivalent Cations (Antacids, Calcium, Iron, Magnesium, Zinc, Bismuth) · Chelation occurs, significantly decreasing the absorption of tetracycline. Separate doses by at least 1-2 hours.
- Methoxyflurane · Concomitant use can cause fatal nephrotoxicity.
- Sucralfate · May impair oral absorption of tetracycline; separate dosing by at least 2 hours.
- Warfarin · May depress plasma prothrombin activity; anticoagulant dosage adjustment may be needed.
モニタリング
- Adverse effects (GI signs, injection site reactions)
- Clinical efficacy
- Periodic renal, hepatic, and hematologic evaluations (with long-term use or in susceptible patients)
過量投与
Tetracyclines are generally well tolerated after acute overdoses. * **Oral Overdose**: Most likely associated with GI disturbances (vomiting, anorexia, diarrhea). Monitor fluids and electrolytes if severe emesis/diarrhea occurs. * **Chronic Overdose**: May lead to drug accumulation and nephrotoxicity. * **Ruminants**: High oral doses can cause ruminal microflora depression and ruminoreticular stasis. * **IV Overdose/Rapid Injection**: Rapid IV injection can induce transient collapse and cardiac arrhythmias, presumably due to chelation with intravascular calcium ions. If rapid IV administration is necessary, pre-treatment with intravenous calcium gluconate is recommended by some clinicians.
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。