Doxycycline
Doxycycline is a broad-spectrum, semi-synthetic **tetracycline antibiotic** derived from oxytetracycline. It is widely used in veterinary medicine due to its favorable pharmacokinetic profile compared to older tetracyclines. **Key Clinical Advantages:** * **High Lipophilicity:** Penetrates tissues exceptionally well, including the central nervous system (CSF), prostate, and eye. * **Renal Safety:** Unlike other tetracyclines, doxycycline is primarily excreted in the feces as an inactive chelate. It does **not** accumulate in patients with renal dysfunction, making it the tetracycline of choice for azotemic patients. * **Heartworm Adjunct:** Doxycycline is a critical component of modern canine heartworm (*Dirofilaria immitis*) treatment protocols. It eliminates ***Wolbachia***, an endosymbiotic bacterium essential for heartworm survival and reproduction, thereby weakening the adult worms and reducing post-adulticide pulmonary pathology. It is highly effective against atypical organisms including *Borrelia* (Lyme disease), *Leptospira*, *Rickettsiae*, *Chlamydia*, *Mycoplasma*, *Bartonella*, and *Bordetella*.
Mecanismo: 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).
Dosificación por especie
- 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.
Vías de administración
Contraindicaciones
- 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
Efectos adversos
- 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)
Interacciones farmacológicas
- 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
Monitoreo
- 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
Sobredosis
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.
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