Pharmacokinetics of cysteine ethyl ester in rat.

1. The pharmacokinetics of the mucolytic compound 35S-cysteine ethyl ester in rat show that it is completely absorbed after oral administration, with a bioavailability of 0.59. 2. By autoradiography, tissue distribution of 35S-cysteine ethyl ester showed a high affinity for the lung, different to that observed with 35S-cysteine. 3. Unchanged cysteine ethyl ester, cysteine and inorganic sulphates were present in the lung. 4. After oral or i.v. administration of 35S-cysteine ethyl ester the total radioactivity excreted in the urine amounted to 16% dose and 40% was excreted in the faeces, following biliary excretion. It was metabolized to inorganic sulphate, cysteine and taurine, which were excreted in the urine.