Serum and urine concentrations of morphine and morphine metabolites in patients with advanced cancer receiving continuous intravenous morphine: An observational study Cancer palliative care

Background:The feasibility and clinical implication of drug monitoring of morphine, morphine-6-glucuronide (M6G)and morphine-3-glucuronide (M3G) need further investigation. This study aimed to determine what predicts serumconcentrations of morphine in cancer patients receiving continuously intravenous morphine, the relationships betweenserum concentration of morphine/its metabolites and urinary concentrations, and the relation between morphineconcentrations and with clinical outcomes.Methods:We collected serum and urine samples from 24 patients with advanced cancer undergoing continuouslyintravenous morphine therapy. Serum samples were obtained at day one. Spot urine samples were collected once dailyon three consecutive days. Pain and adverse drug events were assessed using the Korean version of MD AndersonSymptom Inventory.Results:A total of 96 samples (72 urine and 24 serum samples) were collected. Median dose of morphine was82.0 mg/24 h. In a multivariate analysis, total daily morphine dose was the most significant predictors of bothserum and urine concentration of morphine. Morphine, M6G, and M3G in serum and urine were statistical significantlycorrelated (correlation coefficient = 0.81, 0.44, 0.56;pvalues < 0.01, 0.03, 0.01, respectively).Conclusion:Spot urine concentrations of morphine and its metabolites were highly correlated to those of serum. Totaldose of daily morphine was related to both serum and urine concentration of morphine and its metabolites.