Comparative pharmacokinetics of aditoprim in milk-fed and conventionally fed calves of different ages.

Aditoprim body disposition was described after intravenous and oral administration of 5 or 10 mg kg-1 bodyweight to milk-fed and conventionally fed calves with bodyweights of 80 kg, 160 kg and 210 kg. After intravenous administration to conventionally fed calves, aditoprim total body clearance increased and elimination half-life decreased with age. Oral administration of aditoprim with feed was associated with a longer absorption half-life and consequently longer elimination half-life in the older calves, because the drug was deposited in a functionally mature rumen. The weak base aditoprim is slowly absorbed from the rumen according to the pH partition hypothesis and probable binding to dietary fibres and other macromolecules. The favourable pharmacokinetics of aditoprim indicate a potential use for this antimicrobial in bovine practice, pending further studies on residue depletion profile, safety and therapeutic efficacy.