title: A newly developed precise and sensitive radioimmunoassay for clonidine.
abstract: A new precise and sensitive radioimmunoassay for clonidine has been developed. Synthesis and analysis of the hapten (4-carboxy-clonidine; St 1984) as well as antibody production in rabbits are described in detail. At a final dilution of 1:1000 the resulting immune serum binds 50% of a tritiated clonidine standard containing 1 ng of clonidine. The detection limit of the presented radioimmunoassay for clonidine is 0.1 ng/ml. The coefficient of variation did not exceed 4.3% for any of 7 standard determinations with 5 replicates. There was no relevant cross-reactivity of inactive clonidine metabolites apart from 4-OH-clonidine. To avoid any errors from cross-reaction clonidine was selectively and quantitatively extracted into diethylether from unknown plasma samples. Following concentration of the extracts even such low concentrations as 20 pg of clonidine/ml plasma were detectable. With the radioimmunoassay applied in pharmacokinetic studies a maximal clonidine concentration in blood plasma of healthy human volunteers was determined to 0.6 ng/ml 1.5 h after oral administration of 150 micrograms.
mesh_terms: D000906:Antibodies / Q000032:analysis; D000941:Antigens; D003000:Clonidine / Q000097:blood* / Q000276:immunology; D003429:Cross Reactions; D006241:Haptens / Q000138:chemical synthesis; D006801:Humans; D007700:Kinetics; D008297:Male; D008722:Methods; D011863:Radioimmunoassay
chemical_list: D000906:Antibodies; D000941:Antigens; D006241:Haptens; D003000:Clonidine