Thiamphenicol pharmacokinetics in beef and dairy cattle

The pharmacokinetics of thiamphenicol were investigated in 10 calves and six lactating cows. It was found that this drug is rapidly absorbed (1 5 min) following intramuscular injection with an absorption rate constant and a bioavailability of 8.7 h ‐1 and 84%, respectively. The drug appears to be widely distributed into various body fluids, yielding a volume of distribution (V d(area) ) of approximately 0.9 l/kg. The micro‐rate constants indicated that the antibiotic rapidly diffuses into the peripheral compartment (k 12 > k 21 ). Elimination from plasma is relatively rapid, with a biological half‐life of about 1.75 h. Thiamphenicol appears shortly in milk (15 min) after its intravenous administration, and gives milk to plasma concentration ratios greater than one between 4 and 12 h.