Pharmacokinetics of imidocarb dipropionate in horses after intramuscular administration.
Authors: Belloli C, Crescenzo G, Lai O, Carofiglio V, Marang O, Ormas P
Journal: Equine veterinary journal
Summary
# Imidocarb Dipropionate Pharmacokinetics in Horses Imidocarb is routinely administered intramuscularly to treat *Babesia caballi* infections and prevent babesiosis, yet its behaviour in equine circulation remained poorly characterised until this 2002 investigation. Belloli and colleagues injected eight horses with a single therapeutic dose of 2.4 mg/kg and tracked drug concentration in plasma, faeces, urine and milk using high-performance liquid chromatography over an extended timeframe. Notably, imidocarb became undetectable in plasma within 12 hours post-injection, despite the drug's known clinical efficacy against babesial parasites. This paradox resolves through the drug's rapid sequestration into tissue reservoirs, where it persists long-term in concentrations sufficient for therapeutic activity—a reservoir mechanism explaining why treatment remains effective even when circulating levels fall below detection thresholds. For practitioners, these findings underscore that imidocarb's short plasma half-life does not reflect inadequate therapeutic action, and the prolonged tissue retention may inform dosing intervals and withdrawal periods for competition or food-producing animals.
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Practical Takeaways
- •Imidocarb's disappearance from blood does not indicate elimination from the body—tissue sequestration provides prolonged therapeutic effect for babesiosis treatment and prevention
- •The 12-hour plasma clearance may inform re-dosing intervals and withdrawal periods, as the drug persists in tissues long after blood levels drop
- •Understanding tissue reservoir effects helps explain why single-dose imidocarb protocols remain effective despite rapid plasma clearance
Key Findings
- •Imidocarb dipropionate is rapidly sequestered in tissue storage sites after i.m. administration at 2.4 mg/kg in horses
- •Plasma concentrations became undetectable by 12 hours post-injection despite prolonged body retention
- •The drug exhibits a tissue reservoir effect that may explain its extended therapeutic and prophylactic activity despite absent plasma detection
- •HPLC detection methods confirmed prolonged tissue retention patterns following single i.m. dose