氯四環黴素
氯四環黴素（Chlortetracycline）是一種廣效的第一代**四環黴素類抗生素**。雖然其抗菌譜與土黴素（oxytetracycline）和四環黴素（tetracycline）幾乎相同，但在獸醫學中，它主要作為經濟動物（牛、豬、家禽）的飼料或飲水添加劑使用。 主要臨床特徵包括： * **廣效抗菌：** 對許多黴漿菌（*Mycoplasma*）、螺旋體（包括萊姆病病原）、披衣菌（*Chlamydia*）和立克次體（*Rickettsia*）有效。 * **抗藥性增加：** 許多革蘭氏陽性和陰性細菌（如大腸桿菌、克雷伯氏菌、綠膿桿菌）已產生抗藥性。 * **特寵應用：** 常用於鳥類醫學（特別是治療披衣菌感染）及某些小型哺乳動物，但**嚴禁**用於天竺鼠，因為會引起致命的腸毒血症。
作用機制: Chlortetracycline is a **bacteriostatic** antibiotic that inhibits bacterial protein synthesis. * **Primary Mechanism:** Reversibly binds to the **30S ribosomal subunit** of susceptible organisms → blocks the binding of aminoacyl transfer-RNA to the mRNA-ribosome complex → halts peptide chain elongation. * **Secondary Mechanism:** May also reversibly bind to **50S ribosomes** and alter cytoplasmic membrane permeability. * **Mammalian effects:** At very high concentrations, it can inhibit protein synthesis in mammalian cells, leading to antianabolic effects.
各物種劑量
- Susceptible infections · 25 mg/kg PO q6-8h · PO · q6-8h
- Bacterial conjunctivitis, keratitis, blepharitis, and spontaneous chronic corneal epithelial defects (SCCEDs) · 0.5-2 cm of ointment to affected eye · topical · q6h · 5 days · Used for immunomodulatory mechanism in SCCEDs.
- Chlamydiosis (Small birds) · 0.05% concentration in food · PO · Continuous
- Chlamydiosis (Larger psittacines) · 1% CTC concentration in food · PO · Continuous
- Susceptible infections (Ratites) · 15-20 mg/kg PO three times daily · PO · TID
- Susceptible infections (Pigeons) · 50 mg/kg PO q6-8h; or 1000-1500 mg/gallon drinking water · PO · q6-8h or continuous · In warm weather mix fresh every 12 hours. Calcium inhibits absorption; withhold grit and layer pellets during treatment.
- Susceptible infections · 25 mg/kg PO q6-8h · PO · q6-8h
- To prevent recurrence of mycoplasma or chlamydial conjunctivitis in large catteries · 50 mg per day per cat · PO · q24h · 1 month · Administer soluble chlortetracycline powder in food.
- Feline chlamydial conjunctivitis, mycoplasmal conjunctivitis, bacterial keratitis/blepharitis · 0.5-2 cm of ointment to affected eye · topical · q6h · 5 days · Oral doxycycline is the treatment of choice for feline chlamydial conjunctivitis.
給藥途徑
禁忌症
- Known hypersensitivity to chlortetracycline or other tetracyclines
- Guinea pigs (causes fatal clostridial enterotoxemia)
不良反應
- Gastrointestinal distress (nausea, vomiting, anorexia, diarrhea)
- Discoloration of developing teeth and bones (yellow, brown, or gray)
- Delayed bone growth and healing (at high doses)
- Hepatotoxicity
- Increased BUN (antianabolic effect)
- Ruminal microflora depression and stasis (in ruminants)
- Intravascular hemolysis and hemoglobinuria (with rapid IV injection of propylene glycol-based products)
- Colic, fever, and hair loss (in cats)
- Severe diarrhea (in stressed horses)
- Superinfections (bacterial or fungal overgrowth)
- Photosensitivity
藥物相互作用
- Beta-lactam Antibiotics · Bacteriostatic action of tetracyclines may interfere with the bactericidal activity of penicillins and cephalosporins.
- Aminoglycosides · May interfere with bactericidal activity.
- Digoxin · May increase the bioavailability of digoxin in a small percentage of patients, potentially leading to toxicity.
- Divalent or Trivalent Cations (Antacids, Calcium, Iron, Magnesium, Zinc, Bismuth) · Chelation occurs, significantly decreasing the oral absorption of the tetracycline. Separate administration by at least 1-2 hours.
- Warfarin · May depress plasma prothrombin activity; anticoagulant dosage may need adjustment.
監測
- Clinical efficacy (resolution of infection)
- Gastrointestinal signs (vomiting, diarrhea, anorexia)
- Renal function (BUN, creatinine) and hepatic function, especially with prolonged use or in compromised patients
- Fluid and electrolyte status if severe GI distress occurs
過量
Tetracyclines are generally well tolerated after acute overdoses. * **Oral Overdose:** Most likely associated with gastrointestinal disturbances (vomiting, anorexia, diarrhea). If severe emesis or diarrhea develops, monitor and replace fluids and electrolytes. * **Chronic Overdose:** May lead to drug accumulation and nephrotoxicity. * **Ruminants:** High oral doses can cause ruminal microflora depression and ruminoreticular stasis. * **Intravenous Overdose:** Rapid IV injection of undiluted propylene glycol-based products can cause intravascular hemolysis and hemoglobinuria. Rapid IV injection can also induce transient collapse and cardiac arrhythmias due to chelation with intravascular calcium ions.
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