A 62-year-old client is being initiated on methadone 5 mg PO three times daily for chronic neuropathic pain. The client is also taking ondansetron and ciprofloxacin. Which is the priority nursing assessment and intervention plan?

Methadone is a long-acting mu-agonist with N-methyl-D-aspartate (NMDA) antagonism, useful for chronic pain and opioid use disorder treatment. Three pharmacologic pitfalls dominate NCLEX teaching: (1) variable, long elimination half-life (15 to 60 hours, much longer than the analgesic half-life of 4 to 8 hours) — accumulation is a major risk in days 3 to 7 after initiation or dose change, when respiratory depression peaks; titrate every 5 to 7 days, not daily; never instruct a patient to take more if pain is not controlled in the first days; (2) QTc prolongation and risk of torsades de pointes — obtain baseline ECG, repeat at 30 days and annually or with dose increases above 30 to 40 mg/day, with new symptoms, or when adding QT-prolonging drugs (ondansetron, fluoroquinolones such as ciprofloxacin, amiodarone, antipsychotics, certain antibiotics, methadone itself, electrolyte disturbances of low K and low Mg); avoid combinations when possible; (3) drug-drug interactions through CYP3A4 and CYP2D6 — phenytoin, rifampin, ritonavir, fluvoxamine, and many others alter methadone levels. Naloxone reversal may require an infusion because methadone outlasts naloxone. Increasing the dose every 12 hours, denying QT effect, and reflexively stopping interacting drugs without an alternative are unsafe.

Slow titration plus QT vigilance plus respiratory surveillance peaking on days 3 to 7 is the methadone safety triangle. Stay alert to QT-prolonging combinations.