Fluorescence polarization immunoassay for zidovudine.

We report a fluorescence polarization immunoassay (FPIA) for zidovudine (azidothymidine; Retrovir). This assay is accurate and specific over the clinically relevant range of zidovudine concentrations in serum (from 1 to 1,250 ng/ml; from 0.004 to 4.8 microM) and is unaffected by potentially interfering compounds in the sera of patients with renal or hepatic failure. Cross-reactivity with structural analogs of zidovudine (including zidovudine glucuronide) is less than 0.05%, except for cross-reactivities of 0.2, 0.3, and 0.4% with 3-methylthymidine, 3',5'-dideoxythymidine, and A22U (the optical isomer of zidovudine), respectively. The FPIA for zidovudine is more sensitive and more specific than high-performance liquid chromatography (HPLC); it requires 50 to 60 or 200 versus 500 microliters of serum and is faster to perform (45 specimens per h with the FPIA versus 3 specimens per h with HPLC). The zidovudine FPIA compares well with the radioimmunoassay. A correlation coefficient of 0.992 was observed with 31 serum specimens examined by both methods. All three assays (FPIA, radioimmunoassay, and HPLC) are unaffected by the heat treatment used to inactivate human immunodeficiency virus. The zidovudine FPIA should be particularly useful for analyzing specimens from large numbers of human immunodeficiency virus-infected patients receiving zidovudine in current clinical trials.