Depletion of dietary sulphamonomethoxine and sulphadimethoxine from various tissues of laying hens

1. Sulphamonomethoxine (SMM) or sulphadimethoxine (SDM) was fed to laying hens at 400 mg/kg diet for 5 successive days. After withdrawal of the drugs, contents (mg/kg) of SMM and SDM in the blood, kidney, liver, ovary, muscle and adipose tissue were determined by HPLC. 2. The disappearance of dietary SMM and SDM from the tissues of laying hens was rapid and, except for the liver, was very similar in all tissues. 3. A common biological half-life (t(1/2)) of SMM in the above 6 tissues was estimated to be 5.2 h. The t(1/2) of SDM in the liver was 6.9 h, significantly longer than that of 4.4 h in the other 5 tissues. The values were much shorter than t(1/2) (reported elsewhere) for other drugs. 4. Comparing the data found in this study with those obtained from previous papers, the depletion velocities of SMM and SDM from the hen's body were much faster than those from albumen in egg. The reason for this is probably related to the longer time period over which albumen formation occurs.