多西環素
多西環素是一種廣效、半合成的**四環黴素類抗生素**，衍生自土黴素（oxytetracycline）。由於其與舊型四環黴素相比具有良好的藥代動力學特性，在獸醫學中被廣泛使用。 **主要臨床優勢：** * **高脂溶性：** 組織穿透力極佳，包括中樞神經系統（CSF）、前列腺和眼睛。 * **腎臟安全性：** 與其他四環黴素不同，多西環素主要以無活性的螯合物形式經糞便排泄。它**不會**在腎功能不全的患者體內蓄積，是氮血症患者的首選四環黴素。 * **心絲蟲輔助治療：** 多西環素是現代犬心絲蟲治療方案的重要組成部分。它能消除心絲蟲生存和繁殖所必需的內共生細菌 ***Wolbachia***，從而削弱成蟲並減少殺成蟲治療後的肺部病理變化。 它對非典型病原體高度有效，包括伯氏疏螺旋體（萊姆病）、鉤端螺旋體、立克次體、披衣菌、黴漿菌、巴爾通體和博德特氏菌。
作用機制: Doxycycline is a **bacteriostatic** antibiotic. * **Primary Mechanism:** It reversibly binds to the **30S ribosomal subunit** of susceptible organisms → prevents the binding of aminoacyl transfer-RNA to the mRNA-ribosome complex → **inhibits bacterial protein synthesis**. * **Secondary Mechanisms:** It may also reversibly bind to 50S ribosomes and alter cytoplasmic membrane permeability. * **Anti-inflammatory/Immunomodulatory Effects:** Beyond its antimicrobial properties, doxycycline inhibits matrix metalloproteinases (MMPs) and scavenges reactive oxygen species, which contributes to its efficacy in treating chronic inflammatory conditions (e.g., idiopathic rhinitis, arthritis).
各物種劑量
- Hemotropic mycoplasmosis · 5-10 mg/kg PO once daily for 14 days · PO · q24h · 14 days · Round dose to nearest whole tablet or capsule.
- Bartonellosis · 50 mg (total dose) PO q12h for 14-28 days · PO · q12h · 14-28 days
- Systemic infections, bacteremia · 5-11 mg/kg PO or IV q12h as long as necessary · PO/IV · q12h · As long as necessary
- Ehrlichiosis or Anaplasmosis · 5-10 mg/kg PO q12h for 21 days · PO · q12h · 21 days
- Clinical hemoplasmosis or bartonellosis · 10 mg/kg PO q12-24h · PO · q12-24h
- Toxoplasma gondii · 5-10 mg/kg PO q12h for 4 weeks · PO · q12h · 4 weeks
- Susceptible mycobacterial, L-Forms, or mycoplasma infections · 5-10 mg/kg PO q12h · PO · q12h
- Nocardia (N. nova) infections · 5 mg/kg or higher PO twice daily · PO · q12h · Combination therapy with amoxicillin and clarithromycin.
- Feline chlamydial infections (C. felis) · 10 mg/kg PO once daily for a minimum of 3-4 weeks · PO · q24h · 3-4 weeks
- Susceptible bacterial infections · 10 mg/kg · PO · q24h · As directed · Administer with food or a water bolus to prevent oesophageal ulceration.
- Feline chlamydiosis · 10 mg/kg · PO · q24h · 3-4 weeks · Administer with food or a water bolus.
給藥途徑
禁忌症
- Hypersensitivity to tetracyclines
- Intravenous administration in horses (associated with fatal cardiac arrhythmias)
- First half of pregnancy (can retard fetal skeletal development and discolor deciduous teeth, though less likely than other tetracyclines)
- Pregnant animals
- Animals with evidence of oesophagitis or dysphagia
不良反應
- Vomiting
- Diarrhea
- Anorexia
- Elevated liver enzymes (ALT, ALP)
- Esophageal strictures (especially in cats if dry-pilled)
- Superinfections (non-susceptible bacteria or fungi)
- Photosensitivity (reported in humans)
- Cardiac arrhythmias, collapse, and death (if given IV to horses)
- Nausea
- Diarrhoea
- Oesophagitis
- Oesophageal ulceration/stricture (especially in cats)
- Tooth discoloration (if given during tooth development, though risk is lower than other tetracyclines)
藥物相互作用
- Oral Antacids (Aluminum, Calcium, Magnesium, Zinc, Bismuth) · Chelates with divalent/trivalent cations, significantly decreasing doxycycline absorption. Give at least 1-2 hours apart.
- Bismuth Subsalicylate, Kaolin, Pectin · May reduce gastrointestinal absorption of doxycycline.
- Oral Iron · Decreases tetracycline absorption. Give iron 3 hours before or 2 hours after doxycycline.
- Penicillins / Cephalosporins / Aminoglycosides · Bacteriostatic drugs (doxycycline) may theoretically interfere with the bactericidal activity of these antibiotics.
- Phenobarbital · May decrease doxycycline half-life and reduce serum levels. · moderate
- Warfarin · Tetracyclines may depress plasma prothrombin activity; anticoagulant dosage may need adjustment.
- Antacids · Reduced absorption of doxycycline · moderate
- Calcium salts · Reduced absorption of doxycycline · moderate
- Magnesium salts · Reduced absorption of doxycycline · moderate
- Iron salts · Reduced absorption of doxycycline · moderate
- Phenytoin · May increase doxycycline metabolism, decreasing plasma levels · moderate
- Antacids (Calcium, Magnesium, Iron salts) · Reduced absorption of doxycycline (though less marked than with water-soluble tetracyclines) · moderate
監測
- Clinical efficacy
- Adverse effects (GI upset)
- Liver enzymes (ALT, ALP) with prolonged use
- Clinical response to therapy
- Signs of dysphagia, regurgitation, or oesophagitis (especially in cats)
- Gastrointestinal upset
過量
Doxycycline is generally quite safe in mild overdose situations (except for IV administration in horses). * **Oral Overdose:** Most likely associated with gastrointestinal disturbances (vomiting, anorexia, diarrhea). * **Treatment:** Oral administration of divalent or trivalent cation antacids (e.g., calcium, magnesium, aluminum) can bind the drug in the gut and reduce GI distress. Monitor and replace fluids/electrolytes if severe emesis or diarrhea occurs. * **IV Overdose:** Rapid intravenous injection has induced transient collapse and cardiac arrhythmias in several species, presumably due to chelation with intravascular calcium ions.
VetSheet 藥物參考供持牌獸醫專業人員作臨床決策輔助之用,不能取代專業判斷或廠方最新藥品說明書。