Therapeutic challenges in cancer pain management: a systematic review of methadone.

The proven therapeutic efficacy of methadone in cancer pain is hindered by a challenging pharmacokinetic-pharmacodynamic profile, considerable interpatient variation, and increasing concern about the complexities of dosing. The objective of this study was to assess the evidence for the use of methadone in cancer pain management. The authors conducted a systematic literature search for randomized controlled trials (RCTs) published post the 2007 Cochrane review of methadone in cancer pain. Trial quality was assessed using the Oxford Quality Scoring System and Cochrane Handbook for Systematic Reviews of Interventions. Of the 152 abstracts found, 4 were RCTs (272 participants). Two RCTs compared the efficacy and safety of methadone with placebo or active control and two investigated rotation to methadone from other opioids. The studies used different routes of administration, dosing, initiation, and titration of methadone and distinct pain scoring tools and did not address the issues raised by the Cochrane review. Methadone has an important role in the management of cancer pain, with many advantages including low cost, high oral bioavailability, rapid onset of action, once-daily dosing, and postulated benefits in difficult pain control scenarios. However, due to limited research in this area, methadone dosing remains a challenge, with vigilant dose initiation, adjustment, and monitoring required. There is a need for further studies using standardized methodology to evaluate the optimal dosing strategy of methadone, the effect on different types of pain, and the role of pharmacokinetics and pharmacogenomics in clinical outcomes.