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Medication Absorption after Bariatric Surgery

Absorption of medications varies with each bariatric procedure. Those patients who have opted for the sleeve or gastric band are usually able to still absorb medications as they did prior to weight loss surgery as the small intestine remains unaltered. Those patients who have undergone the Roux-En-Y gastric bypass, distal bypass, or Biliopancreatic Diversion with Duodenal Switch (commonly known as “the switch”) can have absorptive issues with many medications.

Two important concepts to consider for medication absorption are drug solubility and surface area. Both of these things are altered by malabsorptive procedures. Drugs that are based in aqueous (water-like) solutions are more easily absorbed than those in oily solutions, suspensions, or solids. Tablet forms of medications do take time for dissolution and disintegration and thus can affect absorption. Medication solubility is affected by pH. Medications that have an acidic pH are typically absorbed in the stomach; those with an alkaline pH are absorbed in the intestine. Reduced hydrochloric acid (seen with the Roux-En-Y procedure) and reduction in intestinal enzymes (both malabsorptive procedures) also contribute to altered medication absorption. Anatomically, the villi and microvilli of the small intestine have a larger surface area for absorption than does the colon. With bypassing the duodenum and sometimes much of the jejunum, much of surface area is lost and drug delivery is altered. When possible, tablet forms of medications should be changed to liquid (eg. pain medication and antibiotics), subcutaneous (eg. hormones and vitamin B12), intravenous (eg. bisphosphonates and iron), rectal (eg. fever reducers and antinausea medication), vaginal (eg. hormones), intranasal (eg. hormones and B12), and transdermal (eg. blood pressure medications, hormones, pain medications)

Drugs with long “stomach absorptive phases” should be avoided or precautions should be taken with use. Such medications involve NSAIDs (eg. Motrin, Advil, Naproxen), salicylates (aspirin and aspirin containing products), and bisphosphonates (Actonel, Fosamax, Boniva). The goal is to restrict or limit use of these in the Roux-En-Y gastric bypass patient. Acceptable alternatives can be topical or injectable preparations. Acceptable alternatives for pain control can be acetaminophen (Tylenol) based products, tramadol (Ultram), or opiods (hydrocodone, oxycodone) either alone or in combination with acetaminophen.

Though not extended release, certain drugs must either be changed or closely monitored if used. Some examples of more commonly prescribed medications and what occurs are:
1. Enalapril- effect is decreased as absorption occurs in the stomach and small intestine.

2. Lamictal-absorption largely takes place in the stomach and small intestine, so frequent psychiatric monitoring is essential.

3. Metformin-can have slow to incomplete absorption in the small intestine, so daily to twice daily monitoring of blood glucose is essential with use.

4. Metoprolol-absorption takes place in both the stomach and duodenum so frequent monitoring of BP and heart rate may be necessary.

5. Niacin-absorbed mostly in the duodenum so it must be taken with a protein based snack.

6. Zyprexa-primary site of absorption is the stomach. Consideration must be taken in use with the Roux-En-Y gastric bypass patient. Alternative agents should be considered. If use is continued, frequent psychiatric monitoring is essential.

7. Seroquel-absorption takes place in the stomach and duodenum so use must be monitored.

8. Ramipril-absorption is largely altered so other (blood pressure lowering) medications in this class or other classes should be used.

9. Simvastatin-like Ramipril, absorption is altered so other cholesterol lowering medications should be considered.

10. Ambien-this medication has a rapid absorption time so it is preferred that it is taken on an empty stomach. The controlled release version should be avoided (as discussed in the next section).

Finally, a common error seen with the malaborptive surgeries is the use of sustained release medications post operatively by primary care providers and specialists. Formulations such as these are typically absorbed over a 2-12 hour period. Since surface area is largely reduced in the malabsorptive procedures, medications are allowed to quickly pass through the intestine before full absorption is allowed to occur. Prior to and following surgery, it is recommended that delayed preparations (CR, SR, XR, LA) are converted to immediate-release forms and used in more frequency of 2-3 times daily rather than once daily (as seen in the immediate release forms).

Patients who are affected by any of the medications above should first speak to (his,her) pharmacist. The pharmacist can be a wealth of information regarding medications that are acid based or alkaline based and can offer advice for alternative preparations. The pharmacist can work with the patient and physician to ensure medications are taken safely and achieve the effect desired.

Kristine Vanhoose, MSN, APRN, FNP-BC

Nurse Practitioner



Miller, A. and Smith, Kelly, American Journal of Health System Pharmacy (2006) vol. 63 no. 19: 1852-1857.

Myers, Stephen. My Bariatric Surgery blog. http://bariatricsurgeryblog.blogspot.com/2010/03/amiabletotakeextendedrelease-24.html. Accessed August 6, 2012.

Epocrates 2012.

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