Moxidectin oral vs. injectable in goats
American Consortium for Small Ruminant Parasite Control
Moxidectin (Cydectin) is not approved for use in goats; therefore, there are no established withdrawal times (WDT) for meat and milk. FARAD, a national, USDA-sponsored, cooperative project, with a primary mission to prevent or mitigate illegal residues of drugs, pesticides and other chemicals in foods of animal origin, makes recommendations for extra-label drug use in food animals and these recommendations serve as the defacto WDT guidelines that should be followed.
Recently, FARAD came out with a 120-130 day recommended WDT for meat following use of injectable moxidectin. Without data specifically demonstrating that the injectable provides superior efficacy, we decided it was best to withdraw the recommendation for using injectable moxidectin.
Although the blood level data indicates injectable may be the preferred route, whether or not this translates to better efficacy depends on the amount of drug actually getting into the worm. It makes sense that it would since Haemonchus feeds on blood, but it is possible that the oral route might still be better if high levels of the drug are getting into the worm via direct contact in the stomach.
A study was planned this summer at UGA to compare the efficacy of the oral and injectable routes, but not a single farm in Georgia could be found with moxidectin susceptible worms (6/6 were highly resistant). Only large (>100 goats) farms were tested because lots of goats were needed to do the study, so the situation may not be quite as bad on smaller farms. But overall, >50% of all farms tested by DrenchRite at UGA from 2007-2009 had moxidectin resistance. So, moxidectin is on its last legs in goats in the southeastern US either way, and without clinical proof, we feel it is better to stick with the
oral route (if the worms are susceptible) since this route has a reasonable withdrawal time (23 days).
Furthermore, it is important to only use products that are designed for oral administration. Thus, only the sheep oral drench product should be used; the pour-on form for cattle (given orally) should not be used, and is not allowed under extra-label drug use law.