Control of fentanyl plasma levels for postoperative pain relief

The purposes of this presentation are to examine: 1) the accuracy of curren tly available pharmacokinetic computer models in predicting fentanyl plasma levels during the prolonged infusion, and 2) the range of therapeutic wind ow of plasma fentanyl levels required for pain relief. 1. Predictions of the models by McClain, Scott and Shafer were tested again st plasma concentration data in 105 patients undergoing major abdominal sur gery. All these models predicted the measured fentanyl concentration (Cp) w ith reasonable accuracy. However, McClain's model tended to underestimate C p, while Shafer's model tended to overestimate Cp when infusion is extended to 24 h. 2. The minimum effective analgesic concentrations (MEAC) of fentanyl for po stoperative pain relief were examined in 66 patients (aged 24-86 years). Th ere were wide variations in the value of MEAC ranging from 0.5 to 3.9 ng/ml . This wide individual variability existed in both younger and elderly pati ents. Conclusion. Pharmacokinetic computer models are useful to guide the infusio n rate of fentanyl within the therapeutic window However, because of indivi dual variability of MEAC, the infusion rate of fentanyl for postoperative a nalgesia must be titrated according to the need of the individual patients.