The Correlation Between Predicted and Measured Patient Specific Analgesic Concentrations After Intravenous Titration: A Guide for Initial Maintenance Requirements with Methadone

Abstract

The relationship between the analgesic methadone concentrations measured and those predicted using a pharmacokinetic approach were assessed in 22 patients referred for long‐term management of severe pain with intravenous methadone. Five milligrams of methadone were administered IV every 10 minutes until the patient reported a visual analog scale (VAS) pain score of ≤2. Initial maintenance infusion rates were chosen based on the number of 5 mg doses required to produce satisfactory analgesia. Overall the methadone concentrations predicted using pharmacokinetic modeling were in excellent agreement with those actually measured. Over 95% of the variance in the data was explained using this model (r² = 0.9704). Using the rapid titration paradigm described here, one can obtain a reasonable estimate of patient specific analgesic (target) concentration as well as initial infusion requirements for methadone.