Be prepared to adjust dosing of psychotropics after bariatric surgery

Approximately 113,000 bariatric sur­geries were performed in the United States in 2010; as many as 80% of persons seeking weight loss surgery have a history of a psychiatric disorder.^1,2

Bariatric surgery can be “restrictive” (limiting food intake) or “malabsorptive” (limiting food absorption). Both types of procedures can cause significant changes in pharmacokinetics. Bariatric surgery patients who take a psychotropic are at risk of tox­icity or relapse of their psychiatric illness because of inappropriate formulations— immediate-release vs sustained-release—or incomplete absorption of medications. You need to anticipate potential pharmacokinetic alterations after bariatric surgery and make appropriate changes to the patient’s medica­tion regimen.

Pharmacokinetic concerns
Roux-en-Y surgery is a malabsorptive procedure that causes food to bypass the stomach, duodenum, and a variable length of jejunum. Secondary to bypass, iron defi­ciency anemia is a common nutritional complication.

Other changes that affect the pharma­cokinetics of psychotropics after bariatric surgery include:
• an increase in percentage of lean body mass as weight loss occurs
• a decrease in glomerular filtration rate as kidney size decreases with postsur­gical weight reduction
• reversal of obesity-associated fatty liver and cirrhotic changes.

With time, intestinal adaptation occurs to compensate for the reduced length of the intestinal tract; this adaptation pro­duces mucosal hypertrophy and increases absorptive capacity.³

Medications to taper or avoid
The absorption and bioavailability of a medication depend on its dissolv­ability; the pH of the medium; surface area for absorption; and GI blood flow.⁴ Medications that have a long absorp­tive phase—namely, sustained-release, extended-release, long-acting, and enteric-coated formulations—show compromised dissolvability and absorption and reduced efficacy after bariatric surgery.

Avoid slow-release formulations, includ­ing ion-exchange resins with a semiper­meable membrane and those with slowly dissolving characteristics; substitute an immediate-release formulation.

Medications that require acidic pH are incompletely absorbed because gastric exposure is reduced.

Lipophilic medications depend on bile availability; impaired enterohepatic circulation because of reduced intestinal absorptive surface causes loss of bile and, therefore, impaired absorption of lipo­philic medications.

Medications that are poorly intrinsi­cally absorbed and undergo entero­hepatic circulation are likely to be underabsorbed after a malabsorptive bar­iatric procedure.

Lamotrigine, olanzapine, and quetiap­ine may show decreased efficacy because of possible reduced absorption.

The lithium level, which is influenced by volume of distribution, can become toxic postoperatively; consider measuring the serum lithium level.

Disclosures
The authors report no financial relationship with any company whose products are mentioned in this article or with manufacturers of competing products.