四環黴素
四環黴素是一種典型的短效**四環黴素類抗生素**。雖然過去常作為廣效抗菌藥物使用，但由於細菌抗藥性增加，其臨床角色已發生轉變。 在現代獸醫學中： * **小動物臨床**：對於感染性疾病，通常首選去氧羥四環素 (Doxycycline)，因為其組織穿透力較佳且給藥頻率較低。然而，四環黴素常與**菸鹼醯胺 (Niacinamide)** 併用，利用其免疫調節作用來治療免疫介導性皮膚病（如盤狀紅斑性狼瘡、天皰瘡）。 * **大動物臨床**：通常首選氧四環黴素 (Oxytetracycline)。 **臨床要點**： * 對於非典型病原體如*黴漿菌*、*立克次體*、螺旋體（如萊姆病）及*披衣菌*仍然有效。 * 具有顯著的**抗發炎與免疫調節特性**，使其在獸醫皮膚科中具有重要價值。
作用機制: 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.
各物種劑量
- 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
給藥途徑
禁忌症
- Hypersensitivity to tetracyclines
- Pregnancy (last half) - retards fetal skeletal development and discolors teeth
- Young, growing animals (unless benefits outweigh risks)
不良反應
- 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
藥物相互作用
- 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.
監測
- 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
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.
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