Morphine and metabolites plasma levels after administration of sustained release morphine in Roux-en-Y gastric bypass subjects versus matched control subjects.

BACKGROUND: Better knowledge of opioid pharmacology after Roux-en-Y gastric bypass (RYGB) is required for optimizing their use in this growing population.

OBJECTIVE: The aim of this case-controlled pharmacokinetic (PK) study was to compare morphine and its glucuronidated metabolites (morphine-3-glucuronide and morphine-6-glucuronide) plasma PKs between patients with RYGB and their controls.

SETTINGS: University hospital, Lariboisière Hospital, Paris.

METHODS: Thirty milligrams of morphine as a sustained-release formulation was orally administered in 12 women who had undergone RYGB for at least 2 years (RYGB group) and in their nonsurgical controls matched for sex, body mass index (±2 points), and age (±5 yr). Morphine, morphine-3-glucuronide, and morphine-6-glucuronide plasma concentrations over a 12-hour period were determined by a validated method using liquid chromatography mass spectrometry in tandem. Drowsiness, respiratory rate, and oxygen saturation were monitored during the PK visit.

RESULTS: Morphine oral area under the curve (for time 0-12 hr; 115.8 ± 108.0 nmol.hr/L and 86.9 ± 38.8 nmol.hr/L for RYGB group and control group, respectively, P = .71), morphine at maximal concentration, metabolites oral area under the curve (for time 0-12 hr), and other PK parameters were similar between groups. After drug administration, mean drowsiness was superior in RYGB group. Mean respiratory rate and oxygen saturation were similar in both groups.

CONCLUSION: No dose adjustment seems to be needed for sustained release morphine when prescribed to RYGB patients.