Radioimmunoassay for trimeprazine in human plasma

Antisera to trimeprazine were raised in New Zealand white rabbits to an immunogen synthesized by covalent linkage of bovine serum albumin to N-(2-carboxyethyl)desmethyltrimeprazine. By use of an antiserum, a radioimmunoassay for trimeprazine was developed that is able to quantitate 0.38 ng/ml-1 in a 200 microliter plasma sample with a coefficient of variation of approximately 12%. The antiserum did not cross-react with the supposedly pharmacologically inactive metabolite trimeprazine sulfoxide; however, the cross-reactivity with the supposedly active metabolite N-desmethyltrimeprazine is significant (49%). The radioimmunoassay was able to measure the drug and/or N-desalkyl metabolites in plasma samples obtained as late as 24 hr following administration of a single oral dose (10mg) of trimeprazine tartrate. Analysis of the same plasma samples by a published high-performance liquid chromatographic procedure gave values much lower than those obtained by the radioimmunoassay, indicating the N-desalkyl metabolites are produced significantly after trimeprazine oral administration.