Studies of the specificity of an antibody directed against probenecid. Investigations with probenecid analogs

An antibody against probenecid was obtained in rabbits immunized with probenecid conjugated to bovine serum albumin. The antibody exhibited a high degree of specificity (competitive assay) as shown by studies with 25 analogs which included isomers, homologs and metabolites. Interestingly, three analogs (2′-hydroxy, glycine and methyl ester) had a higher affinity than probenecid. The side-chain metabolites all had much lower affinity than the parent drug. Radioimmunoassay was carried out with dextran-coated charcoal and was sensitive to about 1 nanogram. This raises the possibility of radioimmunoassay of probenecid in plasma and tissue.