Oxycodone, Morphine, and Fentanyl in Patients With Chronic Pain: Proposal of Dose-Specific Concentration Ranges

Abstract

Background: Interpreting opioid concentrations is challenging because of the lack of reference ranges. Therefore, the authors aimed to propose dose-specific concentration ranges in serum for oxycodone, morphine, and fentanyl in patients with chronic pain, based on concentration measurements from a large number of patients and supported by theoretical pharmacokinetic calculations and previously published concentrations. Methods: The opioid concentrations in patients undergoing therapeutic drug monitoring (TDM) for various indications (TDM group) and patients with cancer (cancer group) were investigated. Patients were divided based on the daily opioid doses, and the 10th and 90th percentiles of the concentrations in each dose interval were evaluated. In addition, the expected average serum concentrations were calculated for each dose interval based on published pharmacokinetic data, and a targeted literature search for previously reported dose-specific concentrations was performed. Results: The opioid concentrations in 1054 patient samples were included: 1004 in the TDM group and 50 in the cancer group. In total, 607 oxycodone, 246 morphine, and 248 fentanyl samples were evaluated. The authors proposed dose-specific concentration ranges based mainly on 10th–90th percentiles of the concentrations measured in patient samples, whereas the calculated average concentrations and previously published concentrations were used to adjust the ranges. In general, results from calculations and concentrations retrieved from previous literature were within the 10th–90th percentiles of concentrations from patient samples. However, the lowest calculated average concentrations of fentanyl and morphine were below the 10th percentiles of patient samples in all dose groups. Conclusions: The proposed dose-specific ranges may be useful for interpreting steady-state opioid serum concentrations in clinical and forensic settings.