Methadone Pharmacokinetics in End-stage Renal Disease

The goal of this observational study is to describe the influence of renal function on the pharmacokinetics of methadone used through an intravenous patient-controlled analgesia (IV-PCA) pump for the management of acute postoperative pain. After surgery the participants will use an IV-PCA of methadone and blood samples will be withdrawn to measure the plasmatic levels of it. The main question the study aims to answer is: • Is the pharmacokinetic of methadone used in an IV-PCA pump impaired in patients with chronic kidney disease?