CAFFEINE IN PLASMA AND SALIVA BY A RADIOIMMUNOASSAY PROCEDURE

  • 1 January 1976
    • journal article
    • research article
    • Vol. 199  (3) , 679-686
Abstract
Caffeine was analyzed in human plasma and saliva by a simple, rapid and sensitive radioimmunoassay procedure. Immunization of rabbits with an antigen prepared by coupling 7-(5-carboxypentyl)-1,3-dimethylxanthine to bovine serum albumin resulted in the formation of antibodies selective for caffeine as opposed to various mono- and dimethylxanthines, mono-, di- and trimethyluric acids and a variety of common drugs. The radioligand used for competitive binding studies was 7-(2,3-3H2-propyl)-1,3-dimethylxanthine. The procedure permits direct analysis of caffeine in plasma or saliva without extraction. Comparison with a high pressure liquid chromatography method for the analysis of caffeine gave satisfactory results and showed no evidence for interference by metabolites. A caffeine half-life of 4.0 h determined by the radioimmunoassay was in agreement with previous work. Comparison of human plasma and saliva levels by the radioimmunoassay procedure indicated approximately equal concentrations in the 2 fluids.