Thiamphenicol pharmacokinetics in sheep

The pharmacokinetics of thiamphenicol were investigated after intravenous (i.v.), intramuscular (i.m.) and oral (p.o.) administration to sheep. It was found that the drug is almost completely absorbed following intramuscular injection, with a bioavailability of about 87.5%. Thiamphenicol appears to be widely distributed into extravascular compartments, yielding a volume of distribution [V(b)] of approximately 1 l/Kg. Elimination from the blood is relatively rapid, with a biological half-life of about 1.5 h. Oral treatment showed that thiamphenicol is absorbed from the gastrointestinal tract yielding very low plasma concentrations which were maintained for at least 24 h. Although only 30% of the oral dose was systemically available, in contrast to chloramphenicol, thiamphenicol is truly absorbed when given orally to adult sheep. One possible reason for this observation is that rumen flora do not biotransform this drug as they do for chloramphenicol. Metabolism investigations are, however, needed to confirm this finding.