Correlation between myoclonus and the 3-glucuronide metabolites in patients treated with morphine or hydromorphone: a pilot study.

The 3-glucuronide metabolites of morphine and hydromorphone have been implicated as a causative factor for patients exhibiting myoclonus. The primary goal of this study was to determine plasma levels of morphine-3-glucuronide (M3G) or hydromorphone-3-glucuronide (H3G) in patients demonstrating myoclonus and identify any trends or associations between the two. Patients were recruited from San Diego Hospice and the Institute for Palliative Medicine's inpatient unit. A prospective convenience sample comprised of 17 subjects, 12 with myoclonus and 5 without myoclonus. Analysis included demographic, metabolic and clinical variables. Plasma was assayed via high performance liquid chromatography for morphine, M3G, and morphine-6-glucuronide or hydromorphone and hydromorphone-3-glucuronide. No trends or associations were identified between plasma levels of M3G or H3G and myoclonus. Ratio levels of 3-glucuronide metabolite to their corresponding parent opioid were dramatically lower than anticipated. In this small pilot study, it appears that the serum levels of metabolites M3G and H3G do not correlate with myoclonus.