The acetylation‐deacetylation equilibrium of sulfadimidine in ruminant calves

Summary

Plasma disappearance curves of sulfadimidine (SDM) in calves show at high doses a pattern resembling that of capacity‐limited elimination. The half‐life of the first part of the elimination phase of SDM when administered at high doses ranged between 6.4 and 11.5 h, while that of the terminal end of the plasma concentration‐time curves was similar to that obtained at a low level application, ranging between 2.5 and 6.0 h.

The percentage of N₄‐acetylsulfadimidine (N₄‐SDM) in plasma was low, viz. 2.2 to 5.8% of the total sulfadimidine concentration measured. The acetylation‐deacetylation equilibrium was established within 3 h p.i. The N₄‐SDM plasma concentration‐time curves were parallel to those of SDM beyond 3 h p.i. At high doses (66–235 mg/kg) the percentage of N₄‐SDM was slightly higher than that found at the low dose level.

A small proportion of N₄‐acetylsulfadimidine, injected as the parent compound, was deacetylated to SDM. The intrinsic elimination half‐life of N₄‐SDM was 0.9 h. It may be concluded that ultra‐trace concentrations of N₄‐SDM, left in edible tissues of ruminants at slaughter, have in case of negative sulfonamide‐sensitive bioassays no significance for the public health.

Notes

Meat Inspection Service, Wolfskuilseweg 279, Nijmegen, the Netherlands.

Department of Clinical Pharmacy, Sint Radboud Hospital, University of Nijmegen, the Netherlands.