Clearance of sulfamethoxazole in eggs and tissues of chickens.

Clearance of sulfamethoxazole (SMX, or sulfisomezole) in eggs and tissues of chicken after withdrawal of the drug which was medicated feed additively (at 0.2 or 0.4%) or administered intramuscularly (100 mg./kg., twice daily) for 5 successive days was determined using a fluorescamine reagent. Clearance patterns of SMX were found to be different between albumen and yolk. SMX level in albumen diminished linearly to below 0.1 p.p.m. (sensitivity level) by 5 days after the cessation of medication. On the other hand, SMX level in yolk remained at a plateau until 4 days, and thereafter decreased linearly to below 0.1 p.p.m. by 10 days. SMX levels in most tissues diminished below 0.1 p.p.m. by 3 days and those in kidney and skin by 4 days. Clearance patterns in tissue were quite similar to those in egg albumen. Proportion of acetylated-SMX to total-one in both albumen and yolk tended to increase up to 10% with the lapse of time after drug withdrawal. Acetylation was high in liver (36.5-43.6%), spleen skin and fat, but low in breast muscle and kidney (3.7-11%) in the groups of feed addition; while acetylation was low in liver of the group of intramuscular injection.