Drug Distribution in Obesity and following Bariatric Surgery: A Literature Review

Effects of bariatric surgery on drug pharmacokinetics-Preclinical studies

With the rising worldwide obesity rates, bariatric surgeries are increasing. Although the surgery offers an effective treatment option for weight loss, the procedure causes dramatic physiological and metabolic changes. Animal models in rodents provide a valuable tool for studying the systemic effects of the surgery. Since the surgery may significantly influence the pharmacokinetic properties of medications, animal studies should provide essential insight into mechanisms underlying changes in how the body handles the drug. This review summarizes research work in rodents regarding the impact of standard bariatric procedures on pharmacokinetics. A qualitative literature search was conducted via PubMed, the Cochrane Central Register of Controlled Trials (CENTRAL), and EMBASE. Studies that examined bariatric surgery's effects on drug pharmacokinetics in rodent models were included. Clinical studies and studies not involving drug interventions were excluded. A total of 15 studies were identified and assessed in this review. These studies demonstrate the possible impact of bariatric surgery on drug absorption, distribution, metabolism, excretion, and potential mechanisms. Pharmacokinetic changes exhibited in the limited pre-clinical studies highlight a need for further investigation to fully understand the impact and mechanism of bariatric surgery on drug responses.

Implications of Bariatric Surgery on the Pharmacokinetics of Antiretrovirals in People Living with HIV

Bariatric surgery is increasingly applied among people living with HIV to reduce obesity and the associated morbidity and mortality. In people living with HIV, sufficient antiretroviral exposure and activity should always be maintained to prevent development of resistance and disease progression. However, bariatric surgery procedures bring various gastrointestinal modifications including changes in gastric volume, and acidity, gastrointestinal emptying time, enterohepatic circulation and delayed entry of bile acids. These alterations may affect many aspects of antiretroviral pharmacokinetics. Some drug characteristics may result in subtherapeutic exposure and the potential related risk of treatment failure and resistance. Antiretrovirals that require low pH, administration of fatty meals, longer intestinal exposure, and an enterohepatic recirculation for their absorption may be most impacted by bariatric surgery procedures. Additionally, some antiretrovirals can interact with the polyvalent cations in supplements or drugs inhibiting gastric acid, thereby preventing their use as these comedications are commonly prescribed post-bariatric surgery. Predicting pharmacokinetics on the basis of drug characteristics solely proved to be challenging, therefore pharmacokinetic studies remain crucial in this population. Here, we discuss general implications of bariatric surgery on antiretroviral outcomes in people living with HIV as well as drug properties that are relevant for the choice of antiretroviral treatment in this special patient population. Additionally, we summarise studies that evaluated the pharmacokinetics of antiretrovirals post-bariatric surgery. Finally, we performed a comprehensive analysis of theoretical considerations and published pharmacokinetic and pharmacodynamic data to provide recommendations on antiretrovirals for people living with HIV undergoing bariatric surgery.

Bariatric Surgery can Lower the Efficacy of DOACs

A 39-year-old woman who was taking the contraceptive pill was admitted with right leg deep venous thrombosis (DVT). She was started on apixaban tablets, but after 8 days developed proximal progression of the DVT and pulmonary embolism. Her medical history later showed a history of sleeve gastrectomy. The patient responded to a vitamin K antagonist after heparin. The failure of the antithrombotic drug shed light on the efficacy and changed pharmacodynamics of direct oral anticoagulants (DOACs) after bariatric surgery in the absence of commercially available blood monitoring tests.

Oral Anticoagulant Use After Bariatric Surgery: A Literature Review and Clinical Guidance

Bariatric surgery may alter the absorption, distribution, metabolism, or elimination (disposition) of orally administered drugs via changes to the gastrointestinal tract anatomy, body weight, and adipose tissue composition. As some patients who have undergone bariatric surgery will need therapeutic anticoagulation for various indications, appropriate knowledge is needed regarding anticoagulant drug disposition and resulting efficacy and safety in this population. We review general considerations about oral drug disposition in patients after bariatric surgery, as well as existing literature on oral anticoagulation after bariatric surgery. Overall, available evidence on therapeutic anticoagulation is very limited, and individual drug studies are necessary to learn how to safely and effectively use the direct oral anticoagulants. Given the sparsity of currently available data, it appears most prudent to use warfarin with international normalized ratio monitoring, and not direct oral anticoagulants, when full-dose anticoagulation is needed after bariatric surgery.

The influence of bypass procedures and other anatomical changes in the gastrointestinal tract on the oral bioavailability of drugs

The gastrointestinal (GI) tract plays an important role in the absorption of orally administered drugs. However, in some cases the anatomy of the GI tract is changed due to GI surgery, which has the potential of influencing drug bioavailability. In this review, we aim to compile, review, and comment the existing but sometimes fragmented scientific data regarding the impact of GI surgery on the oral bioavailability of drugs. Relevant reports were gathered through the PubMed database from database inception through January 2012. Drugs for which at least one trial or case report suggested a change in oral bioavailability or absorption caused by GI surgery are discussed in detail. Major methodological differences, such as study design, number of subjects and choice of reference group, were observed in the reported studies. Predicting the impact of GI surgery on the oral bioavailability was therefore difficult to perform, even the most sophisticated classification systems could not be used for predicting purposes.

Pharmacology of morphine in obese patients: clinical implications

Morphine is an analgesic drug used to treat acute and chronic pain. Obesity is frequently associated with pain of various origins (e.g. arthritis, fibromyalgia, cancer), which increases the need for analgesic drugs. Obesity changes drug pharmacokinetics, and for certain drugs, specific modalities of prescription have been proposed for obese patients. However, scant data are available regarding the pharmacokinetics and pharmacodynamics of morphine in obesity. Prescription of morphine depends on pain relief but the occurrence of respiratory adverse effects correlates with obesity, and is not currently taken into account. Variations in the volume of distribution, elimination half-life and oral clearance of morphine, as well as recent advances in the respective roles of drug-metabolizing enzymes, catechol-O-methyltransferase and the mu opioid receptor in morphine pharmacokinetics and pharmacodynamics, may contribute to differences between obese and non-obese patients. In addition, drug-drug interactions may alter the disposition of morphine and its glucuronide metabolites, which may either increase the risk of adverse effects or reduce drug efficacy.

Acute cellular transplant rejection following laparoscopic adjustable gastric banding in a morbidly obese patient post heart transplantation

BACKGROUND

Obesity is a worldwide health problem that is often worsened after organ transplantation. As obesity is associated with increased incidence of metabolic syndrome, cardiovascular events and death, it is essential to control weight and avoid weight gain in patients especially following cardiac transplantation. Of the various strategies that are available for weight reduction, bariatric surgery seems to be the most effective in achieving weight loss and in maintaining the reduced body weight. However, this has not been frequently performed in organ-transplant recipients.

CASE REPORT

We are reporting a unique case of a bariatric surgery procedure performed in a patient after cardiac transplantation. A 30-year-old African-American man with a history of end-stage heart failure due to idiopathic dilated cardiomyopathy underwent orthotopic cardiac transplantation. Three years after transplantation, the patient underwent laparoscopic adjustable gastric banding surgery for morbid obesity. Two months later, the patient presented with severe heart failure and was diagnosed with acute cellular rejection as evidenced by endomyocardial biopsy results despite continued combined immunosuppressive therapy that had not been changed but with significantly reduced blood levels of calcineurin inhibitors.

CONCLUSION

We hypothesize that the altered gastro-intestinal motility and delayed gastric emptying due to laparoscopic adjustable gastric banding may have caused incomplete absorption of the administered immunosuppressant drugs in this particular case, as evidenced by the low tacrolimus level, resulting in acute cellular rejection of the transplanted heart, which has never been described before.

Recommended nutritional supplements for bariatric surgery patients

OBJECTIVE

To review nutritional supplements commonly required after bariatric surgery to provide a practical guide and reference source for generalist healthcare providers.

DATA SOURCES

A PubMed literature search (1988-July 2008) was conducted, using the search term nutritional deficiency after bariatric surgery, and was limited to English-language literature on adult (aged >19 y) human subjects. Additional references from the selected literature were also included.

STUDY SELECTION AND DATA EXTRACTION

Data were extracted from large clinical series and practice guidelines whenever possible. Case reports were used only when they were the sole information source.

DATA SYNTHESIS

Nutritional deficiencies that occur after bariatric surgery depend significantly on the type of surgery performed. Restrictive procedures such as gastric banding are the least likely to cause nutritional deficits, since none of the intestine is bypassed. Malabsorptive procedures such as biliopancreatic diversion or mixed restrictive/malabsorptive procedures (eg, Roux-en-Y gastric bypass) can result in serious nutritional problems when patients do not take required supplements after surgery. Vitamins and minerals that are commonly deficient in this circumstance include vitamin B(12), calcium, vitamin D, thiamine, folic acid, iron, zinc, and magnesium. Rare ocular complications have been reported with hypovitaminosis A.

CONCLUSIONS

Healthcare professionals, especially those who practice outside large bariatric centers, must be aware of the supplements required by patients who have had bariatric surgery. Many patients fail to follow up with the surgery centers and are managed by their primary care teams and community pharmacists, especially in the selection of multivitamin and nutritional supplements.

Pharmacokinetics of mycophenolic acid, tacrolimus and sirolimus after gastric bypass surgery in end-stage renal disease and transplant patients: a pilot study

BACKGROUND

Promising data regarding the safety and efficacy of gastric bypass surgery (GBS) as an option to address obesity in the transplant population are emerging. The data lack on how GBS may alter the pharmacokinetics (PK) of modern immunosuppression. The objective of this study was to describe the alterations in the PK of modern immunosuppressants and the GBS population.

METHODS

Data are presented on six subjects who participated in this trial--four were on dialysis and two were renal transplant recipients. Dialysis-dependent bypass subjects received a single dose of 6 mg of sirolimus, two 4-mg doses of tacrolimus and two 1000-mg doses of mycophenolate mofetil (MMF) over the 24-h study period. Transplant recipients continued their current regimen. Maximum plasma concentration (C(max)), time to reach the maximum plasma concentration (T(max)) and the area under the plasma concentration vs. time curve (AUC(0-12) and AUC(0-infinity) where appropriate) were calculated for tacrolimus, sirolimus, mycophenolic acid (MPA) and mycophenolic acid glucuronide (MPAG).

RESULTS

Significant inter-patient variability in the C(max), T(max) and AUC of tacrolimus, sirolimus MPA and MPAG was observed. A notable difference in the AUC:dose ratio for tacrolimus was seen when comparing data with published data in the non-bypass population. Similar differences in PK were seen with sirolimus, MPA and MPAG.

CONCLUSIONS

When comparing the PK of sirolimus, tacrolimus, MPA and MPAG to published PK data in the non-bypass population, significant differences are observed. It is likely that transplant recipients with GBS would need higher doses of tacrolimus, sirolimus and MMF to provide similar exposure to a non-bypass patient.

Nursing Challenges in the Administration of Oral Antidepressant Medications in Gastric Bypass Patients

More than half of gastric bypass patients take antidepressants preoperatively, presenting some unique considerations with this patient population. The challenges associated with antidepressant medications are experienced both preoperatively and postoperatively. As the gastric bypass option becomes more readily used in the treatment of obesity, the requirement for understanding the effect of this procedure on any alteration of medications will become more clinically important. The purpose of this paper is to present an overview of the potential challenges in providing optimal patient care for the gastric bypass patient who is taking antidepressant medications.

Medication and nutrient administration considerations after bariatric surgery

PURPOSE

Medication and nutrient administration considerations after bariatric surgery are discussed.

SUMMARY

Bariatric surgery is categorized by surgical technique (i.e., restrictive procedure or a combination of restrictive and malabsorptive procedures). Roux-en-Y gastric bypass is the most frequently performed bariatric surgery in the United States. Patients who have undergone this surgery are at risk for nutrient deficiencies. Several factors, such as pH and absorption sites, should be considered when providing these patients with appropriate supplementation. Drug solubility and surface area for absorption are also affected by gastric bypass procedures. By bypassing major portions of the small intestine, Roux-en-Y procedures drastically reduce the surface area for absorption. These changes may warrant manipulation in drug route or dose to ensure adequate delivery. Drugs with long absorptive phases that remain in the intestine for extended periods are likely to exhibit decreased bioavailability in these patients. The reduced size of the stomach after surgery can place patients at risk for adverse events associated with some medications. Medications implicated in such adverse events include nonsteroidal antiinflammatory drugs, salicylates, and oral bisphosphonates. Drugs that are rapidly and primarily absorbed in the stomach or duodenum are likely to exhibit decreased absorption in patients who have had combination restrictive-malabsorptive procedures. Because reduced drug absorption may result in decreased efficacy rather than toxicity, increased patient monitoring for therapeutic effects can help detect potential absorption problems.

CONCLUSION

Selection of appropriate nutrient salts can improve nutrient replacement in patients who have undergone bariatric surgery. Changes in dosage forms based on drug characteristics can improve bioavailability.