Plasma bromocriptine assays must have high sensitivity because plasma concentrations are low, and high specificity because bromocriptine is extensively metabolised. This paper describes the simple preparation of a radioiodine-labelled derivative of dihydroergocriptine and its use in a radioimmunoassay employing an antiserum directed against the intact bromocriptine molecule. The method could measure plasma bromocriptine at concentrations of 0.05 nmol/L, had between-assay coefficients of variation of less than 10% and was more convenient than previous assays using tritium radiolabels.
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