Determination of zidovudine concentration in serum by enzyme-linked immunosorbent assay and by time-resolved fluoroimmunoassay

Between 1985 and 1986, the drug zidovudine (also known as AZT) was shown to inhibit the human immunodeficiency virus (HIV), and it is used currently to treat acquired immunodeficiency syndrome (AIDS) and AIDS-related complex (ARC), which are caused by HIV infection. Two chemical methods, high-performance liquid chromatography (HPLC) and radioimmunoassay (RIA), have been used to determine the levels of zidovudine in body fluids. Two immunological methods, an enzyme-linked immunosorbent assay (ELISA) and a time-resolved fluoroimmunoassay (TR-FIA), which do not involve the use of radioactivity, were developed to determine zidovudine levels in the body. These newly developed methods may be well suited for laboratories not licensed to use radioactivity. Both ELISA and TR-FIA measure anti-AZT antibodies, which are immune system proteins that specifically bind to the drug AZT or zidovudine. Levels of AZT detected by anti-AZT antibody are then quantified by alkaline phosphatase enzyme activity in ELISA, and by degree of fluorescence, the emission of light upon exposure to ultraviolet radiation, in TR-FIA. The results show that the range of AZT levels that could be detected by ELISA was 125 to 4,000 nanomolar AZT, and by TR-FIA, 5 to 4,000 nanomolar. The speed and sensitivity of TR-FIA make it generally preferable to ELISA. Results obtained by ELISA, TR-FIA, HPLC, and RIA were consistent. (Consumer Summary produced by Reliance Medical Information, Inc.)