Pharma Focus Asia

Bioavailability of Methadone After Sleeve Gastrectomy: A Planned Observational Case Study

Abstract:

Although there are no absolute contraindications to bariatric surgery, most bariatric surgeons consider that patients with ongoing illicit drug use should not undergo such procedures. The lack of clear recommendations within this field makes morbidly obese patients on opioid-replacement therapy a sub-group at risk for treatment refusal. There is little evidence to provide guidance on these matters. Of the few relevant studies that exist, one found patients with past substance abuse to be at higher risk for dropout during the assessment process before bariatric surgery.

Objective

Morbidly obese patients on opioid- replacement therapy may be at risk for treatment refusal with regard to bariatric surgery. However, patients on opioid replacement may have the personal skills to facilitate the lifestyle changes required for successful outcomes after bariatric surgery. This planned case observation assessed the effects of sleeve gastrectomy on the pharmacokinetic properties of methadone.

Methods

A white woman in her 40s on methadone maintenance therapy and with morbid obesity was referred for bariatric surgery. Serial blood samples for methadone concentration measurements were obtained before and at 5 days and 1, 7, and 11months after surgery.

Findings

Serum methadone concentrations increased from before to 5 days after surgery and continued to increase for 7 months thereafter. The pre-dose measurementat11monthspostoperatively suggests a further increase compared with the previous pre-dose measurements.

Implications

Clinicians should beware the potential for altered effects of methadone after bariatric surgery. We recommend hatserum concentrations be routinely measured pre-and post- operatively, and that the dose be adjusted according to these measurements and regular clinical assessments.

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