US Pharm. 2012;37(9):HS-12-HS-16.

Obesity continues to be an epidemic affecting a staggering proportion of the U.S. population. The latest CDC data reveal that, in 2009–2010, almost 41 million women and more than 37 million men aged 20 years and older were obese—more than 35% of the population.¹ Individuals who are overweight or obese have an increased risk of all-cause mortality and a much greater risk of various health conditions, including coronary heart disease, hypertension, type 2 diabetes, dyslipidemia, stroke, gallbladder disease, osteoarthritis, sleep apnea and respiratory problems, and endometrial, breast, prostate, and colon cancers, among others.^2,3 Additionally, women may be significantly affected by other obesity-associated diseases, such as gynecologic abnormalities (i.e., problems with menses and fertility), as well as disorders such as stress incontinence. Among obesity-related conditions, heart disease, cancer, stroke, and diabetes are among the top 10 causes of death in women.⁴ Clearly, treating obesity is essential to women’s health.

Bariatric surgery is an obesity treatment that has been performed over the years with a variety of approaches, and the number of procedures performed has increased as the struggle with this epidemic continues. The American Society for Metabolic and Bariatric Surgery estimates that the number of bariatric procedures in the U.S. increased from 13,365 in 1998 to 150,000 in 2005, and to around 200,000 in 2007.⁵ Given the large percentage of the population affected by obesity, these numbers will probably continue to rise. As the number of patients who have had bariatric surgery increases, the pharmacist can play a crucial role in determining needed medication adjustments to optimize medication therapy in these patients.

BARIATRIC SURGERY: QUALIFICATIONS AND TYPES OF PROCEDURES

Qualifications

In order to determine which patients are possible candidates for bariatric surgery, further classification of obesity is needed. The National Institutes of Health’s clinical guidelines on identifying and treating obesity define obesity as a BMI ≥30 kg/m².² Severity of obesity is further categorized into classes I, II, and III, with some sources going beyond class III to subcategorize obesity severity. Class I is defined as a BMI of 30.0 to 34.9, class II is a BMI of 35.0 to 39.9, and class III (extreme obesity) is a BMI of ≥40 kg/m². Further breakdown of obesity prevalence data from CDC 2007–2008 statistics reveals specifics as to what proportion of the U.S. population falls into classes II and III: In 2007–2008, 14.3% of adults aged 20 years or older had a BMI of ≥35 kg/m², and 5.7% had a BMI ≥40 kg/m².⁶

The aforementioned clinical guidelines on obesity, as well as other publications on bariatric surgery for severe obesity, provide guidance as to which patients may be candidates for this treatment.^2,7 Bariatric surgery may be an option in patients with a BMI ≥40 kg/m² and in those with a BMI ≥35 kg/m² who have comorbid conditions, so both class II and class III patients are potential candidates. Patients must also have tried and failed traditional, less invasive means of weight loss; have acceptable operative risks; and be able to participate in treatment and follow-up, as well as understand the surgical procedure and what practices they must follow in the long term.

Types of Bariatric Procedures

To fully understand the potential impact of bariatric surgery on drug therapy and other considerations, the various types of procedures must be examined. Bariatric procedures generally either use gastric restriction to stimulate weight loss by limiting food intake and causing an early feeling of satiation or are a hybrid of gastric restriction and induction of some type of malabsorption in the gastrointestinal (GI) tract.⁵ Procedures that involve gastric restriction alone include laparoscopic adjustable gastric banding, vertical banded gastroplasty, and sleeve gastrectomy. Procedures that combine gastric restriction and malabsorption include Roux-en-Y gastric bypass and biliopancreatic diversion with duodenal switch. One of the early procedures designed for weight loss, jejunoileal bypass, was a purely malabsorptive procedure in which the stomach was kept intact, but most of the intestines were bypassed.⁸ Owing to the significant complications that patients experienced with this type of procedure, however, this type of surgery is no longer recommended.

Gastric Restriction: Laparoscopic adjustable gastric banding involves wrapping an inflatable band around a small portion of the upper stomach, creating a small area where food can enter and a narrow opening to the rest of the stomach.⁹ The band is connected via tubing to a subcutaneous reservoir to allow saline to be injected to control the degree of gastric restriction. In this procedure, the stomach is not removed and the intestines are not bypassed. Sleeve gastrectomy is another restrictive procedure in which most of the stomach is removed, leaving a sleeve- or cylinder-shaped stomach. Vertical banded gastroplasty involves stomach stapling to partition off a small part of the stomach for the esophagus to empty into, and also uses a band to create a narrow opening to the rest of the stomach.¹⁰

Combined Gastric Restriction and Malabsorption: In Roux-en-Y gastric bypass, a small pouch is created from the upper part of the stomach and separated from the remainder of the stomach.⁹ The small intestine is then separated into two limbs at the middle part of the jejunum (bypassing rest of stomach and duodenum), and the lower portion (alimentary/Roux limb) is connected via anastomosis to the newly created gastric pouch. The lower part of the stomach and the upper small intestine (biliopancreatic limb) are then reconnected via anastomosis further down the jejunum, creating a “Y” configuration. There are variations in how long these limbs are made and how far down the biliopancreatic limb is reconnected, which can affect absorption significantly, since a shorter common channel below the reconnection can limit contact with biliary and pancreatic secretions.^5,9

Biliopancreatic diversion with duodenal switch involves less gastric restriction than Roux-en-Y gastric bypass, but a large portion of the stomach is removed using the sleeve gastrectomy procedure described above. For the malabsorptive component of biliopancreatic diversion, the portion of intestine that is bypassed is much longer than with Roux-en-Y.¹¹ The duodenum is cut about 2 cm from the stomach, and the lower part of the small intestine (latter part of ileum, about 50-100 cm from colon) is reconnected where the duodenum was cut. The bypassed limb that was severed from the stomach is reconnected to the lower part of the small intestine to create a small common channel to the colon in a fashion similar to the Roux-en-Y procedure.

Variations: Of the available bariatric surgery procedures, Roux-en-Y gastric bypass and laparoscopic adjustable gastric banding are the types most commonly performed.¹² These procedures therefore are the ones pharmacists are most likely to encounter in patients, but they are not the only available options, and they are also subject to a number of surgical variations; additionally, in some patients, multiple or combination procedures may have been performed. It is important to keep the specific patient and procedure(s) in mind when considering potential drug therapy implications.

POTENTIAL DRUG CONSIDERATIONS

There are multiple factors for a pharmacist to consider in the postoperative medication management of a bariatric surgery patient. These include how the procedure relates to the drug’s mode of absorption; how the drug is released; other properties of the drug and how they will impact a patient who has had surgical resection or GI-tract alteration; how the drug’s properties relate to a patient struggling with obesity; how drug distribution is affected overall by obesity; and changes in patient medication needs as weight loss occurs.

Medication Absorption

There are multiple steps in the process of medication absorption, as well as a number of complex factors to consider. When a medication is given orally versus IV, the processes that a medication goes through to be absorbed and the medication’s bioavailability must be taken into account. When medications are given in a solid dosage form (e.g., tablet or capsule), disintegration, dissolution, and solubility are key.^13,14 The stomach is the primary site for drug disintegration; the mixing involves a combination of saliva, gastric acid, and movement to break down the dosage form and allow for smaller particle sizes that are more easily absorbed in the GI tract. This action could be substantially reduced in the case of any bariatric procedure involving gastric restriction because of the limited potential for this to occur in a smaller area of stomach.

Dissolution of solid dosage forms also may be impaired because of restriction, and solubility can be altered, particularly in cases in which the pH of the stomach environment has changed.^13,14 In procedures such as Roux-en-Y gastric bypass, vertical-banded gastroplasty, and those involving sleeve gastrectomy (in which part of the stomach is partitioned off or removed), drugs no longer pass through the majority of the stomach, where most of the acid-producing cells are housed. This creates a more alkaline environment that can affect the disintegration, dissolution, and solubility of some medications.

Oral-solution formulations would be expected to be less impacted by changes in these processes since the drug particles are already dissolved. Therefore, dosage-form options should be taken into consideration for bariatric surgery patients postoperatively.^13,14 The discussed changes are important considerations in cases of restrictive procedures, but patients who have had their intestines altered require further examination of the potential impact of their bariatric procedure owing to the great amount of drug absorption that occurs in the small intestine.

The small intestine is a complex organ with a vast surface area because of villi and other features; a multitude of cell types; and neural and vascular innervation that allow for multiple mechanisms affecting absorption.¹⁵ Some of the factors that should be considered include passive diffusion of medications across the epithelium of the GI tract; the effect of transport functions (efflux and uptake) on medication absorption; presystemic metabolism, in which prodrugs require transformation into their active form; medications that rely on mixing with bile acids and enterohepatic circulations for maximum absorption; and the overall effect on site, timing, and extent of absorption, since GI length and mucosal exposure are being substantially reduced.^13,14

Recommending Medication Adjustments

A key area where pharmacists can make recommendations for medication adjustments is dosage form. The pharmacist should consider recommending formulations that do not rely heavily on the stomach for disintegration and dissolution (e.g., liquid forms, orally disintegrating tablets, nonoral forms); he or she should also contemplate switching the patient to immediate-release formulations, since extended-release and sustained-release formulations generally have slow dissolution and an extended absorption period that could cause the medication not to be absorbed in cases when part of the intestine is bypassed and the length of the intestine is reduced.^13,14,16,17

Other drug properties that should be considered in post–bariatric surgery patients include the propensity of a medication to irritate the GI tract and the tendency of certain drugs to promote weight gain and increase appetite.^13,14,16,17 Data are limited regarding pharmacokinetics in patients who are obese and those who have undergone bariatric surgery; however, attention should be paid to how drug distribution and absorption are affected by obesity, given how hydrophilic or lipophilic the drug is, what types of tissues it subsequently distributes into (lean body mass or fatty tissue), and the effect of obesity on medication clearance.¹⁸

All this should be kept in mind while recognizing that a key strategy involves dosing and monitoring based on therapeutic outcome.¹⁸ It is important to remember that medication needs can change in the post–bariatric surgery patient as weight loss occurs and chronic conditions improve.¹⁸ These conditions include—but are not limited to—many of the obesity-related conditions previously mentioned, such as heart disease and related disorders (diabetes, hypertension, dyslipidemia, etc.), respiratory problems, and osteoarthritis.

SELECTED ISSUES AFFECTING WOMEN’S HEALTH

The discussed considerations are applicable to both women and men who have undergone bariatric surgery, but some key areas are worth examining in terms of women’s health given the obesity-related conditions that women face and the medications used to treat these and other conditions in women.

Contraception

In women, fertility problems can be related to obesity.^2,3 Although data on the effect of bariatric surgery on fertility is limited, it is well established that weight loss can improve fertility, and increased fertility after surgery is suggested in the bariatric population as well.^19-21 It is estimated that almost half of bariatric procedures are performed in women aged 18 to 45 years, so it is crucial to consider the impact on fertility in this patient population.¹⁹

Since oral contraceptives (OCs) may be subject to extensive first-pass metabolism and enterohepatic circulation, absorption and efficacy may be reduced in bariatric surgery patients, especially considering the low hormonal dosages used in OCs.^13,20,21 Given the potential for increased fertility and decreased OC efficacy and the paucity of clinical data, the pharmacist may consider recommending other forms of contraception to patients, including barrier methods and non-OCs such as intrauterine devices, vaginal rings, and injectable contraceptives, keeping in mind the potential effects of obesity on volume of distribution and drug concentrations in the plasma.^20,21

Another issue not specifically related to contraception but important in post–bariatric surgery in women of reproductive age is that, according to guidelines, iron supplementation may be needed to prevent nutritional anemias, especially in menstruating women.⁵ The guidelines also contain information regarding giving vitamin C with iron to increase absorption given the need for an acidic environment.

Osteoporosis

A major women’s health issue in general, osteoporosis is especially important to consider in bariatric surgery patients, who may be at greater risk owing to decreased intake of nutrients and the possibility of reduced absorption of calcium and fat-soluble vitamins such as vitamin D.^16,21,22 Multivitamin supplementation including calcium and vitamin D is generally recommended following bariatric surgery.⁵ An important point to remember regarding patients who have undergone a procedure involving restriction in which the acid-producing cells have been partitioned off is that the stomach will generally have a higher pH.^13,14,16

Another important consideration is the potential for absorption issues with calcium carbonate in these patients.^16,22,23 The National Osteoporosis Foundation encourages patients to take calcium supplements with food to increase stomach acid production for optimal absorption, while pointing out that calcium citrate can be absorbed at any time.²⁴ Data suggest that calcium carbonate absorption is impaired when stomach acidity is decreased.^16,25 Considering this information, calcium citrate is a reasonable recommendation for pharmacists to make to bariatric patients. Absorption and GI toxicity are issues with bisphosphonate treatment for osteoporosis, so the use of IV formulations should be considered.^5,16,21,22 Depending upon the scenario, alternative osteoporosis treatments may be kept in mind.

Mental Health

Extremely obese patients are more likely to have psychiatric disorders, most commonly mood disorders.⁵ These patients also may experience increased symptoms of depression and other psychiatric disorders. Additionally, depression is more common in women than in men.²⁶ Given the large proportion of women affected by obesity and undergoing bariatric surgery, psychiatric disorders in this population and the medications used to treat them are an important consideration for pharmacists. Examination of the pharmacokinetics of various medication classes in the bariatric surgery population has brought to light some issues with psychiatric medications regarding site of absorption based on data for the individual agent, bioavailability changes when the medication is administered with food, and drug-distribution problems in obese patients.^13,14,16,18

Another important consideration in the treatment of psychiatric disorders in this population is the propensity of these medications to cause weight gain and/or increase appetite. Since many antidepressants, antipsychotics, and other agents used for psychiatric disorders have this potential, medication therapy in the bariatric surgery patient should be closely examined by the pharmacist in this regard, and any needed changes made to optimize a patient’s therapy.¹⁶

CONCLUSION

There are a multitude of factors to consider in optimizing medication use in patients who have undergone bariatric surgery. Pharmacists can play a key role in identifying ways to prevent and correct problems by taking into account each patient’s specific needs and utilizing their knowledge of drugs. This is especially crucial in the absence of sufficient clinical data examining potential medication issues in this patient population. Obesity affects women in numerous ways. Although many of the challenges seen and recommendations that can be made hold true for both men and women, particular attention is needed in the areas discussed, as well as other areas involving needs that are unique to women or where women may be disproportionately affected.

REFERENCES

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