The pharmacokinetics of promazine and its metabolites after acute and chronic administration to rats--a comparison with the pharmacokinetics of imipramine.

This study was aimed to investigate the pharmacokinetics of promazine (a phenothiazine analogue of imipramine) after its single and repeated administration. Male Wistar rats received promazine as a single injection (10 mg/kg ip) or they were treated chronically with the neuroleptic, once a day for two weeks. Plasma and brain concentration of promazine, desmethylpromazine and promazine sulphoxide were determined using the HPLC method devised by us. The results of the present study were compared with our earlier data obtained in analogous experiments with imipramine. The obtained data showed that the pharmacokinetics of promazine and imipramine was similar, though certain differences could be noticed. Both those drugs were unevenly distributed throughout the body, occurring in low concentrations in the blood plasma and reaching considerably higher concentrations in the brain. However, the uptake of promazine by the brain was more efficient than that of imipramine. The brain/plasma AUC ratio after a single dose amounted to 28.72 for promazine and 12.78 for imipramine. Their demethylated metabolites behaved in a similar way, where as the level of promazine sulphoxide in the brain was three times lower than that in the plasma. Chronic treatment with promazine or imipramine increased concentrations of the parent compounds and their demethylated metabolites, and prolonged their half-life in the plasma and brain. The plasma level of promazine sulphoxide did not change, and its brain level was decreased by chronic treatment with promazine. The half-life of promazine sulphoxide was prolonged in the plasma but shortened in the brain after repeated administration of promazine. The observed considerable amounts of desmethylpromazine and promazine sulphoxide, formed in vivo, suggest that the two compounds are major metabolites of promazine, and that the metabolic pattern of promazine in the rat and man is similar.