Analysis of Morphine and its Major Metabolites by Differential Radioimmunoassay

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Abstract
The analysis of morphine, morphine-3-glucuronide (M-3-G) morphine-6-glucuronide (M-6-G) by differential radioimmunoassay using idodinated label and three different antisera is described. These methods were used to measure concentrations of morphine and its conjugated metabolites in human plasma, over a 3-h period, following a single 10 mg intravenous dose. In 13 patients peak concentrations of M-3-G (739 nmol/L±73.7 SEM) were approximately 10 times greater than those of M-6-G (71-3 nmol/L±8-6 SEM). Times to reach these peaks were similar for both metabolites. Decay of morphine from plasma followed a biexponential pattern with a mean terminal half-life of 59.3 min (±81 SEM, n=11). Accurate determination of the half-lives of the glucuronides was not possible due to the short sampling period, but M-6-G seemed to have a similar half-life to morphine, while M-3-G was eliminated more slowly.

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