Patterns of care and side effects for patients prescribed methadone for treatment of chronic pain

Abstract

Objectives: This manuscript evaluates physician monitoring practices and incidence of cardiac side effects following initiation of methadone for treatment of chronic pain as compared to patients who began treatment for chronic pain with morphine sustained release (SR).

Design: We retrospectively reviewed medical record data on all new initiations of methadone and compared results of physician monitoring practices to patients with new initiations of morphine SR. A standardized chart tool was used to capture clinical data. Data related to health service utilization and clinical diagnoses were obtained from the VA clinical information system.

Setting: A single VA Medical Center in the Pacific Northwest.

Patients: Chronic pain patients prescribed methadone (n=92) or morphine (n=90) in the calendar year 2008.

Results: There was no difference between patients prescribed methadone versus patients prescribed morphine SR in the likelihood of receiving an electrocardiogram (ECG) prior to initiating medication (53 percent versus 54 percent) or in the year after opioid initiation (37 percent versus 40 percent). The two groups also did not differ in rates of developing prolonged rate-corrected (QTc) intervals (>450 ms) (11 percent versus 17 percent). Seventy-two percent of all patients discontinued their long-acting opioid regimens before 90 days due to adverse effects or insufficient pain relief.

Conclusion: Despite recommendations for standardized assessment and cardiac risk monitoring, few patients prescribed methadone received an ECG, and this occurred at a rate that did not differ from patients prescribed morphine SR. Patients discontinued both medications at high rates. Further research is needed to evaluate the clinical significance of QTc prolongation in patients treated with methadone.

Figure 1

Patients prescribed methadone (24%) or morphine SR (32%) continued chronic opioid therapy, but a majority of patients in both groups did not. Patients stopped taking either long-acting opioids for several reasons, including prevalence of side effects, limited pain relief, non-compliance, as requested by the patient, not self-administered, or for reasons not reported. (χ²=13.216, p=0.040).