A comparison of two radioimmunoassays for 7-hydroxychlorpromazine: rabbit polyclonal antibodies vs. mouse monoclonal antibodies.

Two radioimmunoassays (RIAs) were developed for 7-hydroxychlorpromazine (7-OHCPZ), which is a pharmacologically active chlorpromazine (CPZ) metabolite. One of the RIAs used polyclonal antibodies produced in rabbits immunized with a 7-OHCPZ-protein conjugate, which was prepared by coupling 7-hydroxy-N-(2-carboxyethyl)desmethylchlorpromazine to bovine serum albumin by a mixed anhydride method (90% yield). The other RIA was based on mouse monoclonal antibodies produced by hybridomas against the same conjugate. The mouse monoclonal antibodies were considerably more specific than the rabbit polyclonal antibodies. There was little interference with the measurement of 7-OHCPZ by RIA based on mouse monoclonal antibodies even when the samples were spiked with 7-OHCPZ in the presence of five times excess of CPZ and two major metabolites, CPZ sulfoxide and CPZ-N-oxide. By contrast, there was a significant increase in the apparent concentration of 7-OHCPZ when the same samples were assayed by RIA based on polyclonal antibodies. The RIA based on mouse monoclonal antibodies was applied, together with an RIA for CPZ to determine the concentrations of 7-OHCPZ and CPZ in plasma samples from two healthy volunteers after they had received a single 50 mg p.o. dose of CPZ. To our knowledge, this is the first time that plasma 7-OHCPZ concentrations, measured up to 24 hr after a single dose of CPZ, are reported in humans.