125I-radioimmunoassay for antipyrine

A radioimmunoassay (RIA) for the determination of antipyrine directly in plasma and saliva has been developed using 4-¹²⁵I-iodoantipyrine as the radioligand. The method showed excellent agreement (r=0.98) with a recently reported RIA for antipyrine using ³H-antipyrine as the radioligand. The interassay coefficient of variation for the ¹²⁵I-RIA did not exceed 7.6% and the mean recovery of antipyrine added to plasma or saliva was 101±1.73 (S.E.) over a range of 1.5 to 30 μg/ml. By virtue of its simplicity and low cost, the ¹²⁵I-RIA for antipyrine offers an attractive method for the routine determination of antipyrine levels and subsequent calculation of its half-life in man.