Fate and residues of 14C-chloramphenicol in laying chickens

Studies were conducted to determine the metabolic fate of chloramphenicol (CAP) in White Leghorn using the 14C-labelled compound. In one experiment birds were administered orally via intra-crop, a single dose of 100 mg (equivalent to 66 mg kg-1 body weight) of CAP containing 14 microCi 14C-CAP, and its absorption, elimination and distribution in plasma were recorded. Orally dosed 14C-compound was rapidly absorbed, efficiently distributed in plasma and eliminated in excreta (> 70% in 5 hr). After 5 h, CAP equivalent residues in issues were lower than 15 micrograms g-1 for this treatment. In a second experiment birds were given intra-crop dose of either 0.5 or 5 mg of CAP (each dose contained 2.5 microCi 14C-CAP) daily for five consecutive days followed by a seven day withdrawal period and elimination of 14C in excreta and eggs was monitored. More than 95% of the administered 14C was eliminated within the first 24 h after dosing. Radiocarbon (14C) was deposited preferentially in yolks compared to albumen or other tissues. Residues declined when feeding was stopped. Various metabolites were isolated and identified by a combination of TLC, LC, and LC-MS. The main metabolic route of CAP in laying hens appears to be the glucuronidation. Cleavage of the dichloroacetate moiety was only a minor route.