Myoclonus associated with high-dose parenteral methadone

Area of Science:

• Palliative Care
• Neuropharmacology
• Oncology

Background:

• Methadone is widely used for pain management and is generally considered non-neuroexcitatory.
• Its clinical use is expanding, necessitating a thorough understanding of its side effect profile.

Observation:

• Two cancer patients receiving high-dose parenteral methadone in hospice care developed myoclonus.
• Myoclonus, or involuntary muscle twitching, emerged as a potential adverse effect of high-dose methadone administration.

Findings:

• The observed myoclonus was potentially linked to the high dosage and/or intravenous route of methadone administration.
• Reducing the methadone dose and switching to an alternative route of administration resolved the myoclonus while maintaining effective pain control.
• Potential mechanisms involve methadone-induced redistribution of receptor saturation at N-methyl-D-aspartate (NMDA) and delta receptors.

Implications:

• This suggests that methadone may possess neuroexcitatory properties under specific conditions, challenging previous assumptions.
• Parenteral administration and high doses of methadone warrant careful monitoring for potential neuroexcitatory side effects in palliative care.
• Ketamine may serve as an alternative pharmacological option for managing intractable pain in patients experiencing methadone-induced myoclonus.