Development of radioimmunoassay for chlorpromazine

Antiserum against chlorpromazine (CPZ) was produced in rabbits immunized with CPZ hapten conjugated to bovine serum albumin. The antiserum was used to develop a radioimmunoassay for CPZ. As little as 10 pg of CPZ can be detected with this radioimmunoassay. Major metabolites, CPZ sulfoxide, Nor1 -CPZ and Nor2 -CPZ are not bound significantly by the antibody unless the concentrations are very high. Although the antibody can bind 7-HO-CPZ, 8-HO-CPZ and promazine, the concentrations required to produce a 50% inhibition of 3H-CPZ-antibody binding are 5-10 times greater than CPZ. The plasma levels of CPZ and some minor metabolites in rats following administration of 10 mg/kg i.v. were determined by radioimmunoassay and showed a biphasic decay curve. Brain levels revealed that following i.v. administration CPZ traverses the blood-brain barrier rapidly and achieves peak concentration within 5 min. Plasma and brain levels can be detected for at least 24 hr.