Medication Therapy after Bariatric Surgery

Bariatric surgery for weight loss is a successful method to improve the quality of life for patients who suffer from morbid obesity. Successful procedures typically result in significant weight loss and improvement of obesity-related comorbid conditions. Unfortunately, bariatric surgery can result in the development of multiple complications including those that occur from use of medications that can be harmful to patients post surgery.

An area of research that is significantly lacking is the management of medications in patients following bariatric surgery. Unfortunately, due to the lack of studies available, general guidelines must be developed from applying knowledge of specific medication characteristic and what is known about nutrient malabsorption following bariatric surgery.

The changes in the gastrointestinal tract following bariatric surgery significantly effect medications that are administered orally. The significant reduction in the area available for medications to come [Page 450]in direct contact with the gastrointestinal surface for absorption effect the amount of medication entering the blood stream. The changes in the acidity of stomach fluids can also affect medication efficacy. The amount of medication that enters the blood stream following oral administration is highly dependent on its ability to enter liquid form, the amount of time it has in direct contact with the gastrointestinal tract, and blood flow to various regions of the gastrointestinal tract where medications are absorbed.

The chemical structure of each medication differs and dictates the type of environment it requires to enter the blood stream. Medications with acidic characteristics are readily absorbed in the acidic environment of the stomach. Medications with slightly acidic properties or those that are alkaline are readily absorbed in the slightly less acidic environment of the intestines. Following malabsorptive/restrictive bariatric procedures such as Roux-en-Y procedures, the stomach's ability to produce stomach acid is reduced. Medications that require an acidic environment may not be fully absorbed and higher doses may be required to improve the medications effectiveness.

The change in acidity may also affect medications that are enteric coated. Enteric coating is designed dissolve in an alkaline environment such as the intestines. The coating prevents medications that may be deactivated from the stomach acid from being released into the stomach or provides a protective barrier against medications that directly irritate the stomach lining. Post surgery, the reduction in stomach acidity may result in a premature dissolution of the enteric coating, potentially exposing the stomach to medications that may harm the integrity of the stomach lining. Similarly, medications that are fat soluble are also readily absorbed in the stomach. The reduction in contact time due to a shortened gastrointestinal tract following surgery may result in decreased absorption and efficacy of fat soluble medications. Higher doses of medications that are fat soluble may be required to provide a therapeutic effect.

Medications administered orally in a solid dosage form are required to dissolve into a solution form prior to being absorbed into the blood stream. Hence, utilization of medications that are commercially available in a liquid or elixir formulation may improve absorption following surgery. Oral formulations that are used to control the rate a medication is absorbed typically require more time in the gastrointestinal tract prior to dissolving into a solution. Medication formulations such as extended-release, delayed-release, and sustained-release formulations can take anywhere from two to 24 hours to be completely absorbed through the gastrointestinal tract and should be avoided due to a possible decrease in medication efficacy.

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