Signs of Methadone Overdose

From the methadone hydrochloride package insert:

Deaths, cardiac and respiratory, have been reported during initiation and conversion of pain
patients to methadone treatment from treatment with other opioid agonists. It is critical to
understand the pharmacokinetics of methadone when converting patients from other opioids (see DOSAGE AND ADMINISTRATION). Particular vigilance is necessary during treatment
initiation, during conversion from one opioid to another, and during dose titration.
Respiratory depression is the chief hazard associated with methadone hydrochloride
administration. Methadone's peak respiratory depressant effects typically occur later, and persist longer than its peak analgesic effects, particularly in the early dosing period. These characteristics can contribute to cases of iatrogenic overdose, particularly during treatment initiation and dose titration.

In addition, cases of QT interval prolongation and serious arrhythmia (torsades de pointes) have
been observed during treatment with methadone. Most cases involve patients being treated for
pain with large, multiple daily doses of methadone, although cases have been reported in patients receiving doses commonly used for maintenance treatment of opioid addiction.
Methadone treatment for analgesic therapy in patients with acute or chronic pain should only be
initiated if the potential analgesic or palliative care benefit of treatment with methadone is
considered and outweighs the risks.

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