Acyclovir
**Acyclovir** is a synthetic purine nucleoside analogue primarily utilized in veterinary medicine for its antiviral properties against specific herpesviruses. Key clinical applications include: * **Avian Medicine**: Treatment and prophylaxis of **Pacheco's disease** (a highly fatal herpesvirus infection in birds). * **Feline Medicine**: Management of **Feline Herpesvirus-1 (FHV-1)** infections, particularly corneal or conjunctival presentations. *Clinical Pearl: It has relatively mild activity against FHV-1 compared to newer antivirals like famciclovir, ganciclovir, or cidofovir, and carries a higher risk of systemic toxicity in cats.* * **Equine Medicine**: Investigational use for **Equine Herpesvirus type-1 (EHV-1)** myeloencephalopathy, though its extremely poor oral bioavailability (<4%) in horses makes therapeutic efficacy challenging. While highly effective in humans, its use in veterinary species is often limited by variable pharmacokinetics, poor oral absorption in certain species (like horses), and potential toxicities (such as nephrotoxicity and bone marrow suppression in cats).
Mecanismo: Acyclovir is a prodrug that requires activation by viral enzymes, making it highly specific to infected cells. 1. **Viral Entry**: Acyclovir enters the virus-infected cell. 2. **Initial Phosphorylation**: It is preferentially phosphorylated by **viral thymidine kinase** into acyclovir monophosphate. 3. **Subsequent Phosphorylation**: Host cell kinases further convert it into the active form, **acyclovir triphosphate**. 4. **DNA Chain Termination**: Acyclovir triphosphate acts as a competitive inhibitor of **viral DNA polymerase**. It incorporates into the growing viral DNA chain → lacks the 3'-hydroxyl group needed for further elongation → causes **premature DNA chain termination** and halts viral replication.
Dosificación por especie
- Herpesvirus-1 infections · 10-25 mg/kg PO twice daily · PO · q12h · Never begin therapy until diagnostic evaluation is completed. May be toxic in cats; monitor CBC every 2-3 weeks.
- EHV-1 outbreaks (prevention or treatment) · 10 mg/kg PO 5 times daily or 20 mg/kg PO q8h · PO · 5 times daily or q8h · Although efficacy is undetermined, anecdotal use may have had some efficacy. However, the drug's very low oral bioavailability suggests that oral dosing is unlikely to be of much benefit.
- Treatment of Pacheco's Disease · 80 mg/kg PO q8h or 40 mg/kg q8h IM · PO/IM · q8h · Maximum 72 hours for IM · Do not use parenterally for more than 72 hours as it can cause tissue necrosis at site of injection.
- Treatment of Pacheco's Disease · 80 mg/kg in oral suspension once daily PO; mix suspension with peanut butter or add to drinking water 50 mg in 4 oz of water · PO · q24h · 7-14 days
- Individual treatment · 80 mg/kg PO or IM twice daily · PO/IM · q12h
- Prophylaxis (Exposed birds) · 25 mg/kg IM once, then acyclovir is added to drinking water at 1 mg/mL and to the food at 400 mg/quart of seed · IM, then PO · Once IM, then continuous PO · Minimum of 7 days · Give IM with caution as it is very irritating.
- Prophylaxis (Quaker parrots) · 80 mg/kg q8h · PO (gavage) · q8h · 7 days
Las dosis son una referencia clínica para veterinarios colegiados. Confirme siempre con la ficha técnica vigente y el paciente individual.
Vías de administración
Contraindicaciones
- Dehydrated states
- Pre-existing renal function impairment
- Hypersensitivity to acyclovir or related antivirals
- Pre-existing neurologic deficits
- Previous neurologic reactions to other cytotoxic drugs
Efectos adversos
- Thrombophlebitis (with parenteral use)
- Acute renal failure
- Encephalopathologic changes (rare)
- Gastrointestinal disturbances (vomiting, diarrhea)
- Leukopenia (cats)
- Anemia (cats)
- Tissue necrosis (if given IM for >72 hours in birds)
Interacciones farmacológicas
- Nephrotoxic medications (e.g., Amphotericin B, Aminoglycosides) · Concomitant administration with IV acyclovir may increase the potential for nephrotoxicity. Amphotericin B may potentiate antiviral effects but significantly increases nephrotoxic risk.
- Zidovudine · Concomitant use may cause additional CNS depression.
Monitorización
- Renal function tests (BUN, Serum Creatinine) with prolonged or IV therapy
- Complete Blood Count (CBC) every 2-3 weeks in cats to monitor for leukopenia and anemia
- Hydration status
Sobredosis
Acute oral overdosage is unlikely to cause significant toxicity. * **Clinical Signs**: Gastrointestinal signs (vomiting, diarrhea, lethargy) predominate. Renal failure is possible with higher doses due to drug crystallization in the renal tubules. Crystalluria and elevated renal values occurred at 188.7 mg/kg in a dog. * **Treatment**: Consider gastrointestinal decontamination at doses of **150 mg/kg or higher**. Below 150 mg/kg, manage symptomatically as GI signs will likely predominate. Ensure adequate hydration to maintain urine flow and prevent crystalluria.
La referencia de fármacos de VetSheet está destinada a veterinarios colegiados como apoyo a la decisión clínica, no sustituye el juicio profesional ni la ficha técnica vigente del fabricante.