Methadone, Morphine, or Oxycodone in Treating Pain in Patients With Cancer

DISEASE CHARACTERISTICS: * Receiving ongoing care in the outpatient medical oncology setting * Self-reported pain (of any cause) for which long-acting strong opioids (morphine or oxycodone) have been prescribed or administered * Oral morphine-equivalent daily dose (MEDD) of existing opioid regimen (long-acting or immediate-release) 40-300 mg/day * Worst pain score on a scale of 0 (no pain) to 10 (worst pain) of ≥ 5 for ≥ 1 week duration based on verbal self-report AND/OR ≥ 1 persistently bothersome symptom attributed to an opioid side effect (e.g., fatigue, confusion, depressed level of consciousness, memory loss, personality change, anorexia, constipation, dehydration, nausea, vomiting, weight loss, pruritus, urticaria, impotence, reduced libido, and urinary retention or hesitancy) PATIENT CHARACTERISTICS: * None of the following conditions that could predispose the patient to prolonged QT interval-associated tachycardia: * Serum potassium \< 3.0 mg/dL * Cocaine abuse within the past 3 months * Family history of sudden death * Advanced heart failure (ejection fraction \< 40% and/or New York Heart Association (NYHA) class III or IV heart disease) * No known or suspected cognitive impairment that could interfere with adherence to the medication plan or self-report of symptoms and side effects * Not pregnant or nursing * Fertile patients must use effective contraception PRIOR CONCURRENT THERAPY: * See Disease Characteristics * More than 4 weeks since prior radiotherapy or surgery for local control of cancer or pain palliation * More than 60 days since prior use of the same long-acting opioid (i.e., the new long-acting opioid) that patient is switching to on the study * More than 12 weeks since prior methadone therapy * More than 3 days since prior and no concurrent transdermal fentanyl, oxymorphone, or buprenorphine * Concurrent systemic anticancer therapy or bisphosphonates allowed provided therapy was initiated ≥ 4 weeks ago * Concurrent tricyclic antidepressants, Nonsteroidal Antiinflammatory Drugs (NSAIDs), anticonvulsants, or other adjuvant analgesics or psychostimulants allowed provided therapy was initiated ≥ 2 weeks ago * Dose expected to remain stable until after the first week of opioid rotation on study * No concurrent methadone maintenance therapy for opioid addiction * No concurrent intrathecal infusion of analgesics * No concurrent antiarrhythmic medications (e.g., amiodarone or quinidine)