Pharmacokinetics of UMF-078, a candidate antifilarial drug, in infected dogs.

The pharmacokinetics of the filaricidal benzimidazole compounds UMF-078 and UMF-289 were evaluated in beagle dogs experimentally infected with Brugia pahangi. Twenty-four infected microfilaremic beagles were selected and randomly allocated into 4 treatment groups of 6 dogs each: oral (PO) UMF-078, PO UMF-289 (the HCl salt form of UMF-078), intramuscular (IM) UMF-078, and untreated controls. Equivalent doses of 50 mg/kg of the free base were given twice a day for 3 days to the 3 groups of treated dogs. Oral absorption is rapid compared with IM dosing; the absorption half-life (K01-HL) for the IM treatment is approximately 14 hr compared with 1 and 2 hr for the PO regimen of salt and free base forms, respectively. The elimination half-lives (K10-HL) for the PO regimens are 13 and 15 hr for the salt and free base forms, respectively. Because of sustained absorption following IM dosing, the K10-HL is prolonged. In contrast to oral administration, IM dosing of UMF-078 provides sustained, relatively low plasma drug levels, with good tolerance and efficacy.