Pharmacokinetics of doramectin and ivermectin after oral administration in horses.
Authors: Pérez R, Cabezas I, Godoy C, Rubilar L, Muñoz L, Arboix M, Castells G, Alvinerie M
Journal: Veterinary journal (London, England : 1997)
Summary
# Editorial Summary: Oral Doramectin versus Ivermectin in Horses Comparing the blood plasma behaviour of two widely-used oral antihelmintics, researchers administered either ivermectin or doramectin paste (both at 0.2 mg/kg) to ten clinically healthy horses and tracked plasma concentrations for up to 75 days using high-performance liquid chromatography. Whilst both drugs demonstrated comparable absorption profiles and reached peak plasma levels similarly, doramectin exhibited a significantly longer terminal elimination half-life, resulting in measurable plasma concentrations persisting for approximately 30 days compared to ivermectin's 20 days. The prolonged retention profile of doramectin generated area-under-the-curve values approximately 30% higher than ivermectin, suggesting greater systemic exposure and potentially superior parasite exposure over the treatment interval. From a practical standpoint, the extended pharmacokinetic profile may offer advantages for maintaining anthelmintic pressure in grazing horses, though practitioners should note this study did not directly compare parasite-killing efficacy between the two compounds. These findings support doramectin paste as a viable alternative to ivermectin for oral parasite control programmes, particularly where extended drug activity might reduce re-treatment frequency or benefit animals with chronic exposure to gastrointestinal parasites.
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Practical Takeaways
- •Doramectin offers a potential alternative to ivermectin for equine parasite control with the advantage of prolonged systemic levels, potentially allowing for extended dosing intervals
- •The extended detectability of DRM in plasma (30 vs 20 days) may provide improved parasite control and reduce re-treatment frequency in practice
- •Both drugs perform similarly during the absorption phase, so choice between them may depend on desired duration of action, cost, and local resistance patterns rather than initial efficacy
Key Findings
- •Doramectin (DRM) demonstrated a significantly longer terminal elimination half-life (P<0.05) compared to ivermectin (IVM) in horses after oral administration
- •DRM showed 30% higher area under the concentration-time curve (AUC) and longer mean residence time than IVM despite similar absorption patterns
- •Plasma concentrations of DRM were detectable for 30 days post-treatment versus 20 days for IVM, indicating prolonged systemic exposure
- •Both drugs showed similar peak concentrations, time to peak, and absorptive half-lives at the 0.2 mg/kg dose in horses