• Sulphonamides;
  • pyrimethamine;
  • plasma half-lives;
  • drug excretion;
  • egg-yolk;
  • egg-albumen

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.