Enhanced plasma and target tissue availabilities of albendazole and albendazole sulphoxide in fasted calves: evaluation of different fasting intervals

The influence of different pre- and post-treatment fasting periods on the p lasma availability and disposition kinetics of albendazole (ABZ) and its su lphoxide metabolite (ABZSO) in cattle was investigated. The effect of fasti ng on the distribution of ABZ and ABZSO to different target tissues/fluids was also characterised. In Experiment I, 35 parasite-free Holstein calves w ere divided into seven groups according to the following feeding conditions and treated intraruminally with ABZ (10 mg/kg): control group (fed ad libi tum), 24 h fasting either prior to (24 h pre-) or post (24 h post-) treatme nt, 24 h fasting with either 6 (6 h pre+18 h post) or 12 h (12 h pre+12 h p ost-) of feed restriction prior to treatment, 12 h fasting either prior to (12 h pre-) or post (12 h post) treatment. In Experiment II, calves from th e same pool of animals were subjected to a 24 h fasting period prior to the same ABZ treatment and killed (two animals) at either 24, 36 or 48 h post- administration to obtain samples of abomasal/intestinal mucosa and fluid co ntents, bile and lungs. Plasma (Experiment I) and tissues/fluids (Experimen t II) samples were analysed by HPLC. All the fasting periods investigated i nduced marked changes to the plasma availability and disposition kinetics o f the ABZSO metabolite. Enhanced plasma availability between 37 and 118%, d elayed peak concentrations and extended mean residence times for ABZSO were observed in fasted compared to fed calves. The changes in plasma kinetics, reflecting an altered quantitative gastrointestinal absorption, were refle cted in increased availability of ABZ and ABZSO in the target tissues/fluid s of fasted calves. The availabilities of ABZ and ABZSO in the gastrointest inal mucosa and fluids in fasted calves were markedly greater than in those fed ad libitum.