BIOAVAILABILITY, PHARMACOKINETICS AND RESIDUES OF CHLORAMPHENICOL IN THE CHICKEN

The pharmacokinetic properties of chloramphenicol were determined in b roiler chickens after two single oral doses (30 and 50 mg/kg body weig ht) and after a single intravenous (i.v.) dose (30 mg/kg body weight). After oral and i.v. administration, the plasma concentration-time gra ph was characteristic of a two-compartment open model. After oral admi nistration (30 and 50 mg/kg), chloramphenicol was absorbed rapidly (ti me to maximal concentration of 0.72 or 0.60 h) and eliminated with a m ean half-life (t1/2beta) of 6.87 or 7.41 h, respectively. The bioavail ability was 29% at 30 mg/kg chloramphenicol and 38% at 50 mg/kg chlora mphenicol. Concentrations greater than 5 mug/ml were achieved at 15 mi n and persisted up to 2 or 4 h post-administration, respectively. Stat istically significant differences between the two routes of administra tion were found for the pharmacokinetic variables. half-lives of both distribution and elimination phases (t1/2alpha, t1/2beta) and apparent volume of distribution [V(d(area))]. The mean t1/2beta) of chloramphe nicol and i.v. administration was 5.23 h. Chloramphenicol was extensiv ely metabolized into dehydrochloramphenicol (DH-CAP), nitrophenylamino propanedione (NPAP) and nitroso-chloramphenicol (NO-CAP) derivatives. Residues of chloramphenicol (CAP) and the three metabolites DH-CAP, NP AP and NO-CAP in kidney, liver and muscle were measured in chickens th at received an oral dose of 50 mg/kg once daily for 4 days. The result s indicate that CAP and DH-CAP residues were cleared slowly and were a t or below the detection limit of 0.005 mug/ml within 12 days after do sing. However, at the time of slaughter (12 days), the NPAP and NO-CAP residues were detected in the tissue.