Chlortetracycline
Chlortetracycline is a broad-spectrum, first-generation **tetracycline antibiotic**. While it shares a nearly identical spectrum of activity with oxytetracycline and tetracycline, it is primarily utilized in veterinary medicine as a feed or water additive for food-producing animals (cattle, swine, poultry). Key clinical features include: * **Broad-spectrum activity:** Effective against many *Mycoplasma*, spirochetes (including *Borrelia*), *Chlamydia*, and *Rickettsia*. * **Increasing resistance:** Many gram-positive and gram-negative bacteria (e.g., *E. coli*, *Klebsiella*, *Pseudomonas*) have developed resistance over time. * **Exotic animal use:** Frequently used in avian medicine (especially for chlamydiosis) and in certain small mammals, though it is strictly contraindicated in guinea pigs due to fatal enterotoxemia. > **Clinical Pearl:** Because of its formulation as a feed/water additive, it is highly practical for herd or flock treatment, but individual dosing in companion animals is less common compared to newer tetracyclines like doxycycline.
กลไกการออกฤทธิ์: 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.
ขนาดยาตามชนิดสัตว์
- 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.
วิธีการให้ยา
ข้อห้ามใช้
- Known hypersensitivity to chlortetracycline or other tetracyclines
- Guinea pigs (causes fatal clostridial enterotoxemia)
อาการไม่พึงประสงค์
- 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
อันตรกิริยาระหว่างยา
- 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.
การติดตาม
- 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
การได้รับยาเกินขนาด
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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