We review the status of radioimmunoassays for detection of abused drugs. Individual assays with use of 125I-labeled antigens are all performed in an identical manner and can be completed in 30 min to 1 h. Combined assays for simultaneous detection of two or more such drugs or assays in which a tritium-labeled antigen is used require 1-2 h for completion. All tests can be performed with 0.1 ml or less of specimen. The assays involving 125I reliably detect urinary concentrations of, per liter, 40-100 mug of morphine, 100 mug of barbiturates, methadone, methaqualone, or benzoylecgonine, and 1000 mug of amphetamine. The assay for morphine involving 3H detects 60 mug/liter. Each assay is capable of providing a qualitative and quantitative estimate of the drugs sought. The 125I-labeled antigens have a usable shelf life of at least two to four months after the antigen is iodinated; the tritium assay is stable for six months. The assays can be performed with use of paper discs that have been suspended in urine and then dried, in place of the liquid specimen. The assays appear to be equally applicable to detection of drugs in urine, blood, saliva, and tissues. All of them are done at ambient temperature and can be used equally well for emergency (stat) tests or mass screening. Except for the benzoylecgonine assay, the clinical reliability of these tests has been demonstrated.
A radioimmunoassay using a 3H- or 125I-labeled morphine antigen has been shown to be of practical value for the rapid detection of nanogram amounts of morphine and morphine analogs in biological fluids [1–3]. A radioimmunoassay for detection of barbiturates by conjugation of a secobarbital derivative to protein was also developed utilizing 14C-labeled pentobarbital or barbital [4,5]. The present report describes our experiences with a practical radioimmunoassay for barbiturates employing a secobarbital derivative labeled with 125I, as the antigen.
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