Ask the Expert: NSAIDs After Bariatric Surgery
Q: Can NSAIDs be used to treat chronic pain in a patient who has had bariatric surgery?
Approximately 150,000 to 160,000 adult patients undergo bariatric surgery every year, according to the American Society for Metabolic and Bariatric Surgery.1 The alterations made to the gastrointestinal (GI) tract in patients who have undergone elective bariatric surgery can have a profound impact on drug safety and efficacy. The absorption of different pharmacologic agents can be drastically altered in these patients. It is important to consider the effects of bariatric surgery when choosing pharmacologic therapy because they can have a direct impact on how we treat a patient’s pain.1
There are a number of different bariatric procedures that are performed today to help patients lose weight. These procedures can be categorized as either restrictive or a combination of restrictive and malabsorptive. Gastric surgeries that are restrictive in nature create a small pouch from the upper portion of the stomach that limits the amount of food that a person can consume but leaves the rest of the GI tract intact. Procedures that are both restrictive and malabsorptive not only create a smaller pouch from the stomach, but they also bypass a portion of the small intestine (generally the duodenum and part of the jejunum). Adjustable gastric banding (Figure 1) and roux-en-Y gastric bypass (Figure 2) are examples of restrictive and combination restrictive/malabsorptive bariatric procedures, respectively.2
Effects of GI System
The restrictive and malabsorptive bariatric procedures each have different effects on drug absorption and bioavailability. Reducing the size of the stomach can impede the disintegration and dissolution of certain drugs. Gastric mixing, which promotes drug disintegration, often is compromised to some extent after gastric procedures. In some cases, this can be overcome by crushing or chewing tablets or capsules, or by simply using a liquid formulation; however, some drugs cannot be crushed and others do not come in liquid formulations.
In addition, many drugs are more soluble in acidic environments and require the low pH of the stomach contents to dissolve. Restrictive gastric surgeries often increase gastric pH due to the separation of the pouch from the gastric fundus or body, which are the areas of the stomach that contain a large majority of the acid-producing parietal cells. The dissolution of acidic or enteric-coated drugs is more likely to be impeded by increases in gastric pH, as these drugs are more soluble in a lower pH environment.3
By removing or bypassing a portion of the small intestine, malabsorptive bariatric surgery can drastically reduce the length and surface area within the GI tract that is available to absorb drugs. Intestinal transit time is increased in these patients, meaning that any drugs taken orally will spend less time in contact with the intestinal mucosa where they would likely be absorbed. Because of this, drug products formulated in extended-release, delayed-release, sustained-
release, enteric-coated, and film-coated preparations should be avoided, since they have slow dissolution properties and may pass through the GI tract before absorption is complete.2,3 Immediate-release dosage forms should be used to avoid this problem and to maintain appropriate pain management.2
Specific Effects on NSAIDs
The reduced stomach size with all types of gastric surgery presents a major problem with the use of nonsteroidal anti-inflammatory drugs (NSAIDs). Administration of NSAIDs in these patients carries an increased risk for serious damage to the stomach pouch, which may result in gastric ulcers. NSAIDs can cause this damage through direct irritation of the GI mucosa due to their acidic properties and through their systemic effects, which include the inhibition of cyclooxygenase (COX)-1 leading to reduced prostaglandin synthesis and a decrease in production of gastric mucous that protects the stomach epithelium from damage.4
Because of these effects, use of NSAIDs in these patients should be avoided if possible, and alternative oral pain medications, such as acetaminophen, should be substituted.2 These alternatives are safer for patients who have undergone bariatric surgery because they do not carry the risk of causing damage to the stomach mucosa; however, the absorption of different pain medications in the post-bariatric surgery population is largely unknown and likely highly variable depending on the specific drug and patient characteristics. When NSAIDs cannot be avoided, it may be beneficial to select an NSAID that is more selective for COX-2 (such as celecoxib [Celebrex] and meloxicam [Mobic, others]), because these will have fewer effects on the secretion of gastric mucous. Addition of a H2 receptor antagonist, proton pump inhibitor, or misoprostol also should be considered with prolonged use of any NSAIDS in this at risk population.4-6
It is important to keep in mind the altered physiology of patients who have undergone bariatric surgery when managing their chronic pain. As obesity rates continue to increase in the United States, the number of people who elect to have bariatric procedures also will likely increase. Avoiding the use of NSAIDs (including salicylates) in these patients will be a priority when considering the safety of the different agents used for pain management. If unavoidable, then a COX-2 inhibitors are preferred. Crushing or chewing solid formulations or using liquid formulations can aid in absorption when drug disintegration is impaired, and acidic drugs may have decreased dissolution and solubility if gastric pH is increased due to surgery. Certain product formulations, such as enteric-coated and extended-release products, should be avoided in patients who have undergone combination restrictive/malabsorptive bariatric procedures since these drug preparations are likely to pass through the GI tract before being completely absorbed. Immediate-release oral products should be used when possible, despite the inconvenience of more frequent dosing parameters. Use of transdermal pain relievers also should be considered because they may represent a practical way to achieve long-lasting and convenient chronic pain relief in patients with bariatric surgery, given the different factors that can affect oral drug absorption.