A radioimmunoassay suitable for screening blood and urine samples for tricyclic antidepressant and some phenothiazine drugs in forensic toxicology is described. The assay displays a remarkably broad spectrum of cross-reactivity that enables therapeutic or subtherapeutic levels of most tricyclic antidepressants and a number of phenothiazines in blood to be detected. The antiserum is commercially available and the radioligand, a radioiodinated conjugate of N-acetyl-L-histidine and nortriptyline, is easily prepared. Blood samples require prior extraction to reduce the background but urine may be assayed directly. 75 microliters of blood or 100 microliter of urine are required. Haemolysis or decomposition of the samples, common anticoagulants and sodium fluoride do not affect the results. Data for 57 compounds are presented.
Two simple and economical radioimmunoassays for methadone in blood or urine are described. Haemolysis, decomposition, common anticoagulants and sodium fluoride do not affect the results. One assay uses commercially-available [1-3H](-)-methadone hydrobromide as the label, while the other uses a radioiodinated conjugate of 4-dimethylamino-2,2-diphenylpentanoic acid and L-tyrosine methyl ester. A commercially-available antiserum is used in both assays. Normethadone and alpha-methadol cross-react to a small extent with the antiserum while methadone metabolites, dextropropoxyphene, dipipanone and phenadoxone have negligible cross-reactivities. The 'cut-offs' of the two assays as described are 30 and 33 ng ml-1 for blood, and 24 and 21 ng ml-1 for urine. The assay using the radioiodinated conjugate can be made more sensitive if required by increasing the specific activity of the label.
A simple and economical radioimmunoassay for benzoylecgonine in blood or urine is described. Haemolysis, decomposition, common anticoagulants and sodium fluoride do not affect the results. A commercially available antiserum is used at a dilution of 1:600. The tracer is radioiodinated p-hydroxybenzoylecgonine. It is prepared by reacting p-acetoxybenzoic anhydride with methyl ecgonine followed by mild hydrolysis and radioiodination by the Iodo-gen method. The product is purified on a disposable silica cartridge and has a specific activity of about 30 TBq mmol-1. Polyethylene glycol is used to separate the bound and free fractions in the assay. The range of the dose-response curve is 0-400 ng ml-1 benzoylecgonine. The assay is largely specific for benzoylecgonine. Cocaine, ecgonine, methylecgonine and cinnamoyl cocaine have slight or negligible cross-reactivities. The inter-assay coefficient of variation is 7.5% and the recovery of benzoylecgonine from 'spiked' blood is 103%. The 'cut-off' is 20 ng ml-1 benzoylecgonine for both blood and urine. Radioimmunoassay and high-performance liquid chromatography results agree well.
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