Radioimmunoassay for clonidine in human plasma and urine using a solid phase second antibody separation.

A reliable, sensitive, and specific radioimmunoassay (RIA) procedure for the quantitation of clonidine in plasma and other biological fluids was developed. The detection limit of the assay is 2 pg based on a 200 microliters sample. Nine commonly used drugs were found not to interfere with the RIA. The utility of the assay was demonstrated in a bioavailability study of clonidine conducted with 24 healthy subjects. Clonidine was readily quantitated in plasma over 4 half-lives. This assay is suitable for pharmacokinetic and bioavailability studies as well as therapeutic drug monitoring of patients.