DETERMINATION OF CONCENTRATION OF ALBENDAZOLE SULFOXIDE IN PLASMA ANDUTERINE FLUID OF HEIFERS

Objectives-To determine time and concentration of peak plasma and uter ine fluid concentrations of albendazole (ABZ) sulfoxide (ABZSO) in hei fers after oral administration of ABZ. Sample Population-25 young Angu s and Simmental heifers maintained on pasture with ad libitum access t o hay and water. Procedure-Heifers were assigned at random to ABZ or c ontrol (water) groups, and were drenched with ABZ suspension at a dosa ge of 15, 30, 60, or 120 mg/kg of body weight, or with water. Plasma w as collected hourly, from 14 to 25 hours after administration of ABZ o r water. After a drug-withdrawal period, heifers were synchronized for estrus and drenched with 60 mg of ABZ/kg, or water (50 ml). Each uter ine horn was flushed. All samples were extracted and subjected to high -performance liquid chromatography analysis. Results-For all groups, h ighest mean +/- SEM plasma concentration of ABZSO was observed between 15 and 16 hours after ABZ administration, at 2.0 +/- 0.4 mu g/ml (15 mg/kg), 5.3 +/- 1.0 mu g/ml (30 mg/kg), 7.4 +/- 1.5 mu g/ml (60 mg/kg) , and 11.1 +/- 2.7 mu g/ml (120 mg/kg). Mean concentration for all ute rine horn fluid samples was 265 +/- 25 ng/ml/horn; range was 79 to 546 ng/ml/horn. The only significant (P = 0.0006) source of variation was the technician performing the flush. Mean concentration for each tech nician was 184 +/- 24 ng/ml/horn and 345 +/- 35 ng/ml/horn. Clinical R elevance-Teratogenic and embryotoxic effects of ABZSO differ for ewes and heifers. Albendazole sulfoxide is detectable in the uterus of heif ers; however, ABZSO peaks in heifer plasma earlier and at a lower conc entration than that reported for ewes, perhaps contributing to differe nces in susceptibility at similar dosages.