Plasma Half‐lives and the Excretion into Egg‐white and ‐yolk of Three Sulphonamides and Pyrimethamine after Medication of Laying Hens

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Abstract
The concentration of drugs in blood plasma and the excretion into egg‐white and ‐yolk were studied after continuous administration for 8 days in the drinking water of 0.1 % sulphanilamide, 0.2 % and 0.1 % sulphadimidine, 0.04 % sulphaquinoxaline and 0.01 % pyrimethamine. During the last two thirds of this period of treatment a state of equilibrium was reached between the drug concentration in the blood plasma and that in egg‐white. No such equilibrium was established between blood plasma and egg‐yolk. Some physical and chemical constants of the drugs (i. e. lipid solubility at pH 7.4 and 6.0 and per cent protein‐bound in blood plasma and egg‐white) have been measured together with some pharmacokinetic parameters in hens (t1/2α, t1/2β, Vd). By using these results the experimental and theoretical distribution ratios between the ultrafiltrate of egg‐white and blood plasma have been calculated. This has not provided any conclusive evidence of the passage of the investigated drugs from blood plasma to egg‐white following the passive diffusion concept; however, the possibility still exists. With regard to the passage of drugs from blood plasma to egg‐yolk, the amount of drug excreted into the egg‐yolk mainly depends on the lipid solubility of the drug in use.