Sensitive and Specific Morphine Radioimmunoassay with Iodine Label: Pharmacokinetics of Morphine in Man after Intravenous Administration

Analysis of morphine in plasma by radioimmunoassay is complicated by interference from morphine metabolites, particularly morphine-3-glucuronide. This interference makes radioimmunoassay a poor technique to study the pharmacokinetics of morphine in man. The method described here is one which uses commercially available anti-morphine antiserum and separating reagent with a simply prepared iodinated morphine derivative. Cross-reactivity to morphine metabolites is negligible and the method correlates well with HPLC. Results obtained for pharmacokinetic parameters after intravenous administration in man are in agreement with published data using GLC or HPLC. The method is inexpensive, simple and rapid; choice of a different antiserum could allow the method to be used for screening for drugs of abuse such as morphine, diamorphine, codeine and dihydrocodeine.