Effect of a Roux-en-Y Gastric Bypass on the Pharmacokinetics of Oral Morphine Using a Population Approach

Impact of bariatric surgery on oral anticancer drugs: an analysis of real-world data

PURPOSE

The number of patients with bariatric surgery who receive oral anticancer drugs is rising. Bariatric surgery may affect the absorption of oral anticancer drugs. Strikingly, no specific drug dosing recommendations are available. We aim to provide practical recommendations on the application of oral anticancer drugs in patients who underwent bariatric surgery.

METHODS

Patients with any kind of bariatric surgery were extracted retrospectively in a comprehensive cancer center. In addition, a flowchart was proposed to assess the risk of inadequate exposure to oral anticancer drugs in patients who underwent bariatric surgery. Subsequently, the flowchart was evaluated retrospectively using routine Therapeutic drug monitoring (TDM) samples.

RESULTS

In our analysis, 571 cancer patients (0.4% of 140.000 treated or referred patients) had previous bariatric surgery. Of these patients, 78 unique patients received 152 oral anticancer drugs equaling an overall number of 30 unique drugs. The 30 different prescribed oral anticancer drugs were categorized as low risk (13%), medium risk (67%), and high risk (20%) of underdosing. TDM plasma samples of 25 patients (82 samples) were available, of which 21 samples post-bariatric surgery (25%) were below the target value.

CONCLUSIONS

The proposed flowchart can support optimizing the treatment with orally administered anticancer drugs in patients who underwent bariatric surgery. We recommend performing TDM in drugs that belong to BCS classes II, III, or IV. If more risk factors are present in BCS classes II or IV, a priori switches to other drugs may be advised. In specific cases, higher dosages can be provided from the start (e.g., tamoxifen).

Management of Pain Medication in Patients With a History of Bariatric Surgery: A Systematic Review

CONTEXT

Obesity prevalence is persistently increasing worldwide. Among surgical therapeutic procedures, bypass surgery and sleeve gastrectomy have shown the best results regarding weight loss, prevention, and treatment of secondary complications. However, these surgeries are associated with an increased risk of malabsorption and metabolic changes that could further affect the pharmacokinetics of drugs. On the other hand, patients with a history of such surgeries are more likely to experience pain and request analgesic initiation or adaptation. The question of how to manage pain medication in these patients is challenging due to their narrow therapeutic indexes.

OBJECTIVES

To summarize the current literature on the impact of bariatric surgery on the subsequent pharmacokinetics of analgesics and propose a multidisciplinary therapeutic attitude to optimize pain management in these patients.

METHODS

We conducted a systematic review that included all pharmacological studies published after 2000.

RESULTS

Unexpectedly, these surgeries seem to increase the bioavailability of drugs by long-term improvement of hepatic function. Yet, the medical community drastically lacks robust guidelines for pain management in those patients. This systematic review aims to bring together pharmacological studies related to the use of pain treatments in patients who underwent bypass surgery or sleeve gastrectomy.

CONCLUSIONS

Caution should be exercised regarding the risk of overdose in every circumstance: treatment initiation, change of doses, or change of molecule. More prospective trials comparing the pharmacokinetics of medications in obese patients with and without prior bariatric surgery are needed.

Bioavailability of Orally Administered Drugs After Bariatric Surgery

PURPOSE OF REVIEW

Oral drug absorption after bariatric surgery is likely to be altered, but the impact of different bariatric surgery procedures on individual drugs is not uniform. The aim of this article is to describe factors influencing the bioavailability of orally administered drugs after bariatric surgery and to provide readers with practical recommendations for drug dosing. We also discuss the medications that may be harmful after bariatric surgery.

RECENT FINDINGS

The fundamental factors for enteral drug absorption are the production of gastric acid; the preserved length of the intestine, i.e., the size of the absorption surface and/or the preserved enterohepatic circulation; and the length of common loop where food and drugs are mixed with digestive enzymes and bile acids. Bypassing of metabolizing enzymes or efflux pumps and changes in intestinal motility can also play an important role. Significant changes of drug absorption early after the anatomic alteration may also be gradually ameliorated due to gradual intestinal adaptation. The most affected drugs are those with low or variable bioavailability and those undergoing enterohepatic circulation. Attention should also be paid to oral drug formulations, especially in the early postoperative period, when immediate-release and liquid formulations are preferred. The changes in oral bioavailability are especially clinically meaningful in patients treated with drugs possessing narrow therapeutic index (e.g., oral anticoagulants, levothyroxine, and anticonvulsants) or in acute conditions (e.g., anti-infectives); nevertheless, it may also influence the therapeutic value of chronic therapy (e.g., antidepressants. antihypertensives, antiplatelets, statins, PPIs, contraceptives, and analgesics); therapeutic effect of chronic therapy is further influenced by pharmacokinetic alterations resulting from weight loss. Therapeutic drug monitoring, periodical clinical evaluation, and adequate dose adjustments are necessary. Due to safety reasons, patients should avoid oral bisphosphonates, regular use of non-steroidal anti-inflammatory drugs, and, if possible, corticosteroids after bariatric surgery.

The Effects of Bariatric Surgery on Pharmacokinetics of Drugs: a Review of Current Evidence

PURPOSE OF REVIEW

Obesity constitutes a major public health concern and has been recognized as an epidemic. To date, bariatric surgery remains the most effective way for substantial long-lasting weight loss in severe obesity. The purpose of this review is to summarize how the pharmacokinetics of drugs are affected by the most common types of bariatric surgery, i.e., Roux-en-Y gastric bypass (RYGB) and sleeve gastrectomy (SG).

RECENT FINDINGS

Limited data are available regarding the changes in pharmacokinetics of drugs after bariatric surgery. The lack of existing guidelines may lead patients to experience drug toxicity or therapeutic undertreatment. Pharmacokinetic parameters that need to be taken into consideration postoperatively include gastric motility, gastric volume, pH, surface area, bile secretions, carrier proteins, and first-pass metabolism. For drugs with a narrow therapeutic index, other factors need to be monitored closely, including plasma drug levels, patients' clinical outcomes, and laboratory markers. Patients should be followed up frequently and treated in accordance with their response to the drug therapy. Bariatric surgery may affect the pharmacokinetics of various drugs, due to the resultant anatomical changes and the substantial weight loss. Therefore, there is a need to identify those potential changes and adjust patients' medication doses in order to achieve higher efficacy and avoid toxicity.

Prescription and consumption of opioids after bariatric surgery: a multicenter prospective cohort study

INTRODUCTION

In the current opioid crisis, bariatric surgical patients are at increased risk of harms related to postoperative opioid overprescribing. This study aimed to assess the extent to which opioids prescribed at discharge after bariatric surgery are consumed by patients.

METHODS

This multicenter prospective cohort study included adult patients (≥ 18yo) undergoing laparoscopic bariatric surgery. Preoperative assessments included demographics and patient-reported measures. Information regarding surgical and perioperative care interventions (including discharge prescriptions) was obtained from medical records. Self-reported opioid consumption was assessed weekly up to 30 days post-discharge. Number of opioid pills prescribed and consumed was compared using Wilcoxon signed-rank test. Zero-inflated negative binomial regression was used to identify predictors of post-discharge opioid consumption.

RESULTS

We analyzed 351 patients (mean age 44 ± 11 years, BMI 45 ± 8.0 kg/m2, 77% female, 71% sleeve gastrectomy, length of stay 1.6 ± 0.6 days). The quantity of opioids prescribed at discharge (median 15 pills [IQR 15-16], 112.5 morphine milligram equivalents (MMEs) [IQR 80-112.5]) was significantly higher than patient-reported consumption (median 1 pill [IQR 0-5], 7.5 MMEs [IQR 0-37.5]) (p < 0.001). Overall, 37% of patients did not take any opioids post-discharge and 78.5% of the opioid pills prescribed were unused. Increased post-discharge opioid consumption was associated with male sex (IRR 1.54 [95%CI 1.14 to 2.07]), higher BMI (1.03 [95%CI 1.01 to 1.05]), preoperative opioid use (1.48 [95%CI 1.04 to 2.10]), current smoking (2.32 [95%CI 1.44 to 3.72]), higher PROMIS-29 depression score (1.03 [95% CI 1.01 to 1.04]), anastomotic procedures (1.33 [95%CI 1.01 to 1.75]), and number of pills prescribed (1.04 [95%CI 1.01 to 1.06]).

CONCLUSION

This study supports that most opioid pills prescribed to bariatric surgery patients at discharge are not consumed. Patient and procedure-related factors may predict opioid consumption. Individualized post-discharge analgesia strategies with minimal or no opioids may be feasible and should be further investigated in future research.

Impact of Bariatric Surgery in the Short and Long Term: A Need for Time-Dependent Dosing of Drugs

Sparse information is available on pharmacokinetic changes of drugs over time after bariatric surgery. By reviewing the literature on the short- and long-term pharmacokinetic changes of drugs, several patterns were identified for 39 drugs. No relevant pharmacokinetic changes were identified for roughly a third of the drugs. Of the remaining drugs, levels were variable and partly unpredictable shortly after the surgery. In the long term, most of the drug levels remain altered, but in some cases they returned to preoperative values. Based on the changes and the efficacy-safety balance of each drug, clinicians may need to perform additional clinical monitoring for specific drugs, including measuring drug levels. This review provides suggestions for clinicians and pharmacists for specific time-dependent drug dosing advice.

Opioid Analgesics after Bariatric Surgery: A Scoping Review to Evaluate Physiological Risk Factors for Opioid-Related Harm

The persisting use of opioids following bariatric surgery has emerged as a prevalent complication, heightening the probability of opioid-related harm (ORM), such as opioid-related fatalities and prescription opioid use disorder (OUD). A comprehensive review of PubMed literature from 1990 to 2023 was conducted to pinpoint physiological influences on postoperative ORM. As a result, we found that patients undertaking bariatric operations often exhibit an inherently higher risk for substance use disorders, likely attributable to genetic predisposition and related neurobiological changes that engender obesity and addiction-like tendencies. Furthermore, chronic pain is a common post-bariatric surgery complaint, and the surgical type impacts opioid needs, with increased long-term opioid use after surgeries. Additionally, the subjective nature of pain perception in patients with obesity can distort pain reporting and the corresponding opioid prescription both before and after surgery. Furthermore, the postoperative alterations to the gastrointestinal structure can affect the microbiome and opioid absorption rates, resulting in fluctuating systemic exposure to orally ingested opioids. The prospect of ORM development post-bariatric surgery appears amplified due to a preexisting susceptibility to addictive habits, surgically induced pain, modified gut-brain interaction and pain management and the changed pharmacokinetics post-surgery. Further research is warranted to clarify these potential risk variables for ORM, specifically OUD, in the bariatric population.

Opioid Use After Gastric Bypass, Sleeve Gastrectomy or Intensive Lifestyle Intervention

OBJECTIVE

To compare opioid use in patients with obesity treated with bariatric surgery versus adults with obesity who underwent intensive lifestyle modification.

SUMMARY OF BACKGROUND DATA

Previous studies of opioid use after bariatric surgery have been limited by small sample sizes, short follow-up, and lack of control groups.

METHODS

Nationwide matched cohort study including individuals from the Scandinavian Obesity Surgery Registry and the Itrim health database with individuals undergoing structured intensive lifestyle modification, between August 1, 2007 and September 30, 2015. Participants were matched on Body Mass Index, age, sex, education, previous opioid use, diabetes, cardiovascular disease, and psychiatric status (n = 30,359:21,356). Dispensed opioids were retrieved from the Swedish Prescribed Drug Register from 2 years before to up to 8 years after intervention.

RESULTS

During the 2-year period before treatment, prevalence of individuals receiving ≥1 opioid prescription was identical in the surgery and lifestyle group. At 3 years, the prevalence of opioid prescriptions was 14.7% versus 8.9% in the surgery and lifestyle groups (mean difference 5.9%, 95% confidence interval 5.3-6.4) and at 8 years 16.9% versus 9.0% (7.9%, 6.8-9.0). The difference in mean daily dose also increased over time and was 3.55 mg in the surgery group versus 1.17 mg in the lifestyle group at 8 years (mean difference [adjusted for baseline dose] 2.30 mg, 95% confidence interval 1.61-2.98).

CONCLUSIONS

Bariatric surgery was associated with a higher proportion of opioid users and larger total opioid dose, compared to actively treated obese individuals. These trends were especially evident in patients who received additional surgery during follow-up.

New persistent opioid use after bariatric surgery: a systematic review and pooled proportion meta-analysis

INTRODUCTION

Increasing evidence suggests surgical patients are at risk for developing new, persistent opioid use (NPOU) following surgery. This risk may be heightened for patients undergoing bariatric surgery. Few studies have evaluated this important long-term outcome and little is known about the rate of NPOU, or factors associated with NPOU for bariatric surgery patients.

METHODS AND PROCEDURE

We conducted a systematic review of MEDLINE, Embase, Scopus, Web of Science, and Cochrane databases in August 2021. Studies were reviewed and data extracted independently by two reviewers following MOOSE guidelines. Studies evaluating bariatric surgery patients reporting NPOU, defined as new opioid use > 90 days after surgery, were included. Abstracts, non-English, animal, n < 5, and pediatric studies were excluded. Primary outcome was NPOU prevalence, and secondary outcomes were patient and surgical factors associated with NPOU. Factors associated with NPOU are reported from findings of individual studies; meta-analysis could not be completed due to heterogeneity of reporting.

RESULTS

We retrieved a total of 2113 studies with 8 meeting inclusion criteria. In studies reporting NPOU rates (n = 4 studies), pooled prevalence was 6.0% (95% CI 4.0-7.0%). Patient characteristics reported by studies to be associated with NPOU included prior substance use (tobacco, alcohol, other prescription analgesics), preoperative mental health disorder (anxiety, mood disorders, eating disorders), and public health insurance. Surgical factors associated with NPOU included severe post-operative complications and in-hospital opioid use (peri- or post operatively).

CONCLUSIONS

NPOU is an uncommon but important complication following bariatric surgery, with patient factors including prior substance abuse, mental health disorders, and use of public health insurance placing patients at increased risk, and surgical factors being complications and peri-operative opioid use. Studies evaluating techniques to reduce NPOU in these high-risk populations are needed.

Considerations for clinical evaluation of the effects of bariatric surgery on the pharmacokinetics of orally administered drugs

Obesity has been a growing worldwide concern, and surgical intervention including bariatric surgery is considered as one of the options for treatment. However, there still is controversy over the change in pharmacokinetics (PKs) of drugs after the surgery. To investigate the potential covariates that can influence the area under the curve (AUC) and maximum plasma concentration (C_max), the design of previous studies was reviewed based on pre-determined eligibility criteria. Each study calculated the ratios of the AUC and C_max before and after bariatric surgery. These studies investigated whether the PK parameters were affected by the time after the surgery or by the type of control group. The ratio of the AUC calculated in the early and late follow-up period was similar across Roux-en Y gastric bypass patients. No significant difference in the PK parameters was found between the pre-surgical patients and matched healthy subjects. However, certain control groups could be preferable depending on the purpose of the clinical trial. Although C_max was inconsistent compared to the AUC, insufficient sampling of the time points may have caused such an inconsistency. This is the first article exploring the appropriate methodology in designing clinical studies for changes in the PK characteristics of orally administered drugs in patients with bariatric surgery.

The Effects of Bariatric Surgery and Gastrectomy on the Absorption of Drugs, Vitamins, and Mineral Elements

Bariatric surgery, which is an effective treatment for obesity, and gastrectomy, which is the primary treatment method for gastric cancer, alter the anatomy and physiology of the digestive system. Weight loss and changes in the gastrointestinal tract may affect the pharmacokinetic parameters of oral medications. Both bariatric and cancer patients use drugs chronically or temporarily. It is important to know how surgery affects their pharmacokinetics to ensure an effective and safe therapy. The Cochrane, PubMed, and Scopus databases were searched independently by two authors. The search strategy included controlled vocabulary and keywords. Studies show that bariatric surgery and gastrectomy most often reduce the time to maximum plasma concentration (t_max) and decrease the maximum plasma concentration (C_max) in comparison with the values of these parameters measured in healthy volunteers. Vitamin and mineral deficiencies are also observed. The effect depends on the type of surgery and the properties of the drug. It is recommended to use the drugs that have been tested on these groups of patients as it is possible to monitor them.

Effect of laparoscopic sleeve gastrectomy on drug pharmacokinetics

INTRODUCTION

Given its feasibility and efficacy, laparoscopic sleeve gastrectomy (LSG) has become a widely accepted bariatric surgery for patients with clinically diagnosed severe obesity. LSG induces anatomical changes and subsequent weight loss which may affect drug pharmacokinetics (PK) and consequently impact dosing regimens. This review aims to examine the effect of LSG on drug PK and identify relevant gastrointestinal physiological alterations.

AREAS COVERED

PubMed, Embase, Scopus, and the Cochrane Library were searched for articles related to drug PK and LSG from inception to July 2021. Moreover, literature concerning postoperative physiological conditions in the gastrointestinal tract, such as gastric pH, gastric emptying, and small bowel transit time, etc., which may affect the PK profile of drug products was also reviewed.

EXPERT OPINION

Although LSG is classified as having restrictive property without malabsorptive bypass, postoperative changes in gastrointestinal physiology and subsequent weight loss may also lead to increased, decreased or unaltered drug exposure levels. General monitoring on drug efficacy or safety using biomarkers is proposed. In addition, therapeutic drug monitoring for those drugs when it is applicable and available is recommended to ensure efficient drug dosing and avoid adverse effects. Further research into many individual drugs are warranted.

Potential gut-brain mechanisms behind adverse mental health outcomes of bariatric surgery

Bariatric surgery induces sustained weight loss and metabolic benefits via notable effects on the gut-brain axis that lead to alterations in the neuroendocrine regulation of appetite and glycaemia. However, in a subset of patients, bariatric surgery is associated with adverse effects on mental health, including increased risk of suicide or self-harm as well as the emergence of depression and substance use disorders. The contributing factors behind these adverse effects are not well understood. Accumulating evidence indicates that there are important links between gut-derived hormones, microbial and bile acid profiles, and disorders of mood and substance use, which warrant further exploration in the context of changes in gut-brain signalling after bariatric surgery. Understanding the basis of these adverse effects is essential in order to optimize the health and well-being of people undergoing treatment for obesity.

Opioid consumption in patients undergoing Roux-en-Y bariatric surgery compared with population controls with and without obesity

BACKGROUND

Patients with obesity are prescribed more opioids than the general population.

OBJECTIVES

To compare opioid consumption in patients with obesity who underwent Roux-en-Y bariatric surgery (RYGB) with population controls with and without obesity, not undergoing bariatric surgery, and to identify characteristics associated with opioid use.

SETTING

This study included all patients with a principal diagnosis of obesity, aged 18-72 years, with a RYGB surgical code in the Swedish Patient Register between 2007 and 2013.

METHODS

RYGB patients (n = 23,898) were age- and sex-matched with 1 control patient with obesity (n = 23,898) and 2 population controls without obesity (n = 46,064). Participants were classified as nonconsumers and consumers based on their opioid dispensations during the 12 months before baseline. Opioid consumption was assessed for 24 months.

RESULTS

Nonconsumers. Within 24 months, a significantly higher proportion of RYGB patients (16.6%) started using opioids compared with the controls with obesity (14.3%, P < .0001) and population controls (5.4%, P < .0001). RYGB patients and controls with obesity had higher median daily intake of opioid morphine equivalent (MEQ) (2.8 mg/d) than population controls (2.5 mg/d, P < .0001). Consumers. Within 24 months, the proportion of RYGB patients and controls with obesity that was using opioids were similar (53.1% and 53.4%), but higher compared to population controls (38.0%, P < .0001). The median daily opioid MEQ was higher among RYGB patients than in population controls (10.5 versus 7.8 mg/d, P < .0001). RYGB patients, overall, had higher incidence of bowel surgery and cholecystectomy compared with controls with obesity and population controls, leading to prolonged opioid use in this group. Opioid consumption in general was associated with chronic pain and psychiatric disorder, which were more common in patients with obesity than in the population controls.

CONCLUSION

RYGB surgery increased the risk of prolonged opioid use in patients with obesity who were nonconsumers before surgery but had no effect on overall opioid use among prior consumers. RYGB-associated complications requiring surgery influenced opioid use for both nonconsumers and consumers. Regular reassessments of pain mechanisms and specific treatment owing to type of pain could prevent unnecessary opioid use in this patient group.

Impact of a severe complication two years after laparoscopic Roux-en-Y gastric bypass: a cohort study from the Scandinavian Obesity Surgery Registry

BACKGROUND

Although severe complications (SCs) after laparoscopic Roux-en-Y gastric bypass (LRYGB) are rare, they can be devastating for the affected patient.

OBJECTIVE

To access the impact of SCs (Clavien-Dindo ≥3b) 2 years after LRYGB by using a nationwide Swedish cohort of 48,201 primary cases between 2007 and June 2016.

SETTING

University hospital, Sweden.

METHODS

Patients with SC were matched 1:1 on age, sex, diabetic status, body mass index (BMI), and year of operation to patients without an SC. Weight loss, patient-scored quality of life (QoL), antidepressant use, proton pump inhibitors (PPI) and opioids, and in-hospital care were gathered from 3 national registers.

RESULTS

A total of 1411 (2.9%) patients suffered an SC and 16 (.03%) died. In total, 1403 patients with SC (mean age, 42 yr; female, 75%; with diabetes, 15.7%; mean BMI, 41.9 kg/m²) could be matched. Both groups had a total body weight loss of 32% at 2 years. A lower physical QoL was observed in SCs throughout the study period. Antidepressant, PPI and opioid use was higher among patients with SC, even 2 years after surgery. At this time point, a doubling of oral morphine equivalents (7.3 to 17.0 mg/d) was found in patients with SC compared with prior to surgery. The SC group required more in-hospital care after the initial 30 days (3.8 versus .9 d in the remaining part of the first year).

CONCLUSION

An SC resulted in higher antidepressant, PPI and opioid use as well as higher need for in-hospital care during the first 2 postoperative years. Affected patients should therefore receive special attention during follow up.

Impact of Bariatric Surgery on Medication Efficacy: an Analysis of World Health Organization Pharmacovigilance Data

Bariatric surgery is the most effective treatment of severe obesity. However, this surgery can have an impact on the bioavailability and metabolism of oral drugs as it modifies absorption, intestinal, and hepatic metabolism, and efflux transporter activity. The clinical impact of such modifications often remains unknown. To investigate, we extracted and summarized all reports of changes in drug efficacy associated with bariatric surgery registered in the WHO pharmacovigilance database. We identified 165 drug reports affecting 128 patients. The majority involved gastric bypass surgery (77.3%). Most reports concerned drug ineffectiveness (74.7%). The most frequent modifications concerned psychotropic drugs with a reduction in efficacy. This study underlines the urgent need for more research to better characterize the impact of bariatric surgery on drug pharmacokinetics and clinical efficacy.

Effects of Obstructive Sleep Apnea and Obesity on Morphine Pharmacokinetics in Children

BACKGROUND

Obesity increases susceptibility to chronic pain, increases metabolism, and is associated with obstructive sleep apnea syndrome (OSAS), all which can complicate perioperative pain management of patients. In addition, obesity and OSAS can cause elevation of the adipose-derived hormone leptin, which increases metabolism. We hypothesized that obesity along with sleep apnea and leptin independently enhance morphine pharmacokinetics.

METHODS

Children 5-12 years of age who were presenting for surgery were administered a morphine dose of 0.05 mg/kg. Blood was collected at baseline and at subsequent preset times for pharmacokinetic analysis of morphine and its metabolites. Three groups were studied: a nonobese group with severe OSAS, an obese group with severe OSAS, and a control group.

RESULTS

Thirty-four patients consisting of controls (n = 16), nonobese/OSAS (n = 8), and obese/OSAS (n = 10) underwent analysis. The obese/OSAS group had a higher dose-adjusted mean maximum morphine concentration (CMAX) over 540 minutes compared to the controls (P < .001) and those with only OSAS (P = .014). The obese/OSAS group also had lower volume of distribution (Vd) when compared to OSAS-only patients (P = .007). In addition, those in the obese/OSAS group had a higher morphine 3-glucuronide (M3G) maximum concentration (P = .012) and a higher ratio of M3G to morphine than did the control group (P = .011). Time to maximum morphine 6-glucuronide (M6G) concentration was significantly lower in both nonobese/OSAS and obese/OSAS groups than in the control group (P < .005). C-reactive protein (CRP), interleukin (IL)-10, and leptin were all higher in the obese/OSAS group than in controls (P = .004, 0.026, and <0.001, respectively), and compared to OSAS-only patients, CRP (P = .013) and leptin (P = .002) levels were higher in the obese/OSAS group.

CONCLUSIONS

The combination of obesity and OSAS was associated with an increase in morphine metabolism compared with that in normal-weight controls. Our previous study in mice demonstrated that obesity from leptin deficiency decreased morphine metabolism, but that metabolism normalized after leptin replacement. Leptin may be a cause of the increased morphine metabolism observed in obese patients.

Long-term opioid use after bariatric surgery

BACKGROUND

Opioid analgesics are often prescribed to manage pain after bariatric surgery, which may develop into chronic prescription opioid use (CPOU) in opioid-naïve patients. Bariatric surgery may affect opioid use in those with or without presurgical CPOU.

OBJECTIVE

To compare CPOU persistence and incidence in a large multisite cohort of veterans undergoing bariatric surgery (open Roux-en-Y gastric bypass, laparoscopic RYGB, or laparoscopic sleeve gastrectomy) and matched nonsurgical controls.

SETTING

Veterans Administration hospitals.

METHODS

In a retrospective cohort study, we matched 1117 surgical patients with baseline CPOU to 9531 nonsurgical controls, and 2822 surgical patients without CPOU at baseline to 26,392 nonsurgical controls using sequential stratification. CPOU persistence in veterans with baseline CPOU was estimated using generalized estimating equations by procedure type. CPOU incidence in veterans without baseline CPOU was estimated in Cox regression models by procedure type because postoperative pain, complications, and absorption may differ by procedure.

RESULTS

In veterans with baseline CPOU, postsurgical CPOU declined over time for each surgical procedure; these trends did not differ between surgical patients and nonsurgical controls. In veterans without baseline CPOU, compared with nonsurgical controls, bariatric patients had higher CPOU incidence within 5 years after open Roux-en-Y gastric bypass (hazard ratio = 1.19; 95% confidence interval: 1.06-1.34) or laparoscopic open Roux-en-Y gastric bypass (hazard ratio = 1.22, 95% confidence interval: 1.06-1.41). Veterans undergoing laparoscopic sleeve gastrectomy had higher CPOU incidence 1 to 5 years after surgery (hazard ratio = 1.28; 95% confidence interval: 1.05-1.56) than nonsurgical controls.

CONCLUSIONS

Bariatric surgery was associated with greater risk of CPOU incidence in patients without baseline CPOU but was not associated with greater CPOU persistence.

Pharmacokinetics of Oral Levonorgestrel in Women After Roux-en-Y Gastric Bypass Surgery and in BMI-Matched Controls

BACKGROUND

Women are advised to primarily use non-oral contraceptive alternatives after Roux-en-Y gastric bypass since it is not known if the surgery affects the pharmacokinetics of oral contraceptives.

METHODS

This is a multi-center, open label, phase 2 pharmacokinetic study performed at the University Hospital of Linköping and the Clinical Trials Center, Department of Obstetrics and Gynecology, Danderyd Hospital, Karolinska Institutet, Stockholm, Sweden. Fifteen women aged 18-40 years who had previously undergone Roux-en-Y gastric bypass surgery and reached a BMI < 30 were included. Fifteen BMI-matched women with no previous history of Roux-en-Y gastric bypass surgery served as a control group. After administration of a single dose of a combined oral contraceptive containing 0.03 mg ethinylestradiol/0.15 mg levonorgestrel, serum levonorgestrel concentrations were determined during a 24-h period using ultra performance liquid chromatography/tandem mass spectrometry. The area under the plasma concentration time curve of levonorgestrel (AUC0-24h) was the main outcome measure.

RESULTS

There were no significant differences in the studied pharmacokinetic parameters, AUC0-24h, total AUC, peak serum concentration (Cmax), time to peak serum concentrations (Tmax), apparent oral clearances of levonorgestrel (CLoral), or terminal half-lives (t½) between the groups.

CONCLUSION

This is to our knowledge the first study to evaluate the pharmacokinetics of oral levonorgestrel in women with a BMI < 30 at least 1 year after RYGB compared with a BMI-matched group of women. We could not find any significant pharmacokinetic differences between the groups, suggesting that oral levonorgestrel may be used in non-obese women after Roux-en-Y gastric bypass once a stable body weight has been reached.

CLINICAL TRIAL NUMBER

EudraCT 2014-004677-17.

Medication Management after Bariatric Surgery: Providing Optimal Patient Care

Substantially altered gastrointestinal anatomy/physiology after bariatric surgery presents new challenges for the proper medication management of these patients; drug absorption and bioavailability may increase, decrease, or remain unchanged post surgery, depending on the specific drug in question and the type of bariatric procedure. In this article, we offer a concise overview of the various aspects of this clinically significant issue, aiming to provide readers with a clear understanding as well as practical tools to handle drug management post bariatric surgery. Realizing the potentially altered pharmacokinetics of various drugs after bariatric surgery is essential for providing optimal pharmacological therapy and overall patient care.

Pharmacokinetic changes post-bariatric surgery: A scoping review

Bariatric surgeries induce structural changes that can alter the absorption of drugs in patients already at risk of polypharmacy. This scoping review aimed to explore pharmacokinetic changes of orally administered drugs in patients post-bariatric surgery, and assess the quality and level of bias. Electronic databases were searched for articles relating to bariatric surgery and pharmacokinetics published between 1998 and 2019. Pre-post studies reporting on pharmacokinetic parameters were included, and the Newcastle-Ottawa Scale was used to assess risk-of-bias. A total of 21 studies were included in this review, and changes in absorption were reported in all included studies across 29 drugs. In 11 studies, this change was reported as statistically significant (p<.05), while six reported a nonsignificant change. More drugs exhibited a shorter Tmax and higher Cmax after surgery than otherwise, however changes in AUC were variable. Four studies were assessed as having fair quality while the remainder of the included studies were of good quality and low risk-of-bias. Bariatric surgery alters the absorption of drugs and several mechanisms are implicated to be responsible. Short and long-term monitoring is recommended in patients post-surgery for clinical changes in response to medications. Future research with a higher number of participants and greater control of variables, such as concurrent medications, malabsorptive disorders, and body composition should be considered.

Pharmacokinetics and Pharmacodynamics of Drugs in Obese Pediatric Patients: How to Map Uncharted Clinical Territories

Clinicians are increasingly faced with challenges regarding the pharmacological treatment of obese pediatric patients. To provide guidance for these treatments, a better understanding of the impact of obesity on pharmacological processes in children is needed. Results on pharmacological studies in adults show however ambiguous patterns regarding the impact of obesity on ADME processes or on drug pharmacodynamics. Additionally, based on the limited research performed in obese pediatric patients, it becomes clear that findings from obese adults cannot be expected to always translate directly to similar findings in obese children. To improve knowledge on drug pharmacology in obese pediatric patients, studies should focus on quantifying the impact of maturation, obesity, and other relevant variables on primary pharmacological parameters and on disentangling systemic (renal and/or hepatic) and presystemic (gut and/or first-pass hepatic) clearance. For this, data is required from well-designed clinical trials that include patients with not only a wide range in age but also a range in excess body weight, upon oral and intravenous dosing. Population modelling approaches are ideally suitable for this purpose and can also be used to link the pharmacokinetics to pharmacodynamics and to derive drug dosing regimens. Generalizability of research findings can be achieved by including mechanistic aspects in the data analysis, for instance, using either extrapolation approaches in population modelling or by applying physiologically based modelling principles. It is imperative that more and smarter studies are performed in obese pediatric patients to provide safe and effective treatment for this special patient population.

Chronic abdominal pain and persistent opioid use after bariatric surgery

Background and aims

Bariatric surgery remains a mainstay for treatment of morbid obesity. However, long-term adverse outcomes include chronic abdominal pain and persistent opioid use. The aim of this review was to assess the existing data on prevalence, possible mechanisms, risk factors, and outcomes regarding chronic abdominal pain and persistent opioid use after bariatric surgery.

Methods

PubMed was screened for relevant literature focusing on chronic abdominal pain, persistent opioid use and pharmacokinetic alterations of opioids after bariatric surgery. Relevant papers were cross-referenced to identify publications possibly not located during the ordinary screening.

Results

Evidence regarding general chronic pain status after bariatric surgery is sparse. However, our literature review revealed that abdominal pain was the most prevalent complication to bariatric surgery, presented in 3–61% of subjects with health care contacts or readmissions 1–5 years after surgery. This could be explained by behavioral, anatomical, and/or functional disorders. Persistent opioid use and doses increased after bariatric surgery, and 4–14% initiated a persistent opioid use 1–7 years after the surgery. Persistent opioid use was associated with severe pain symptoms and was most prevalent among subjects with a lower socioeconomic status. Alteration of absorption and distribution after bariatric surgery may impact opioid effects and increase the risk of adverse events and development of addiction. Changes in absorption have been briefly investigated, but the identified alterations could not be separated from alterations caused solely by excessive weight loss, and medication formulation could influence the findings. Subjects with persistent opioid use after bariatric surgery achieved lower weight loss and less metabolic benefits from the surgery. Thus, remission from comorbidities and cost effectiveness following bariatric surgery may be limited in these subjects.

Conclusions

Pain, especially chronic abdominal, and persistent opioid use were found to be prevalent after bariatric surgery. Physiological, anatomical, and pharmacokinetic changes are likely to play a role. However, the risk factors for occurrence of chronic abdominal pain and persistent opioid use have only been scarcely examined as have the possible impact of pain and persistent opioid use on clinical outcomes, and health-care costs. This makes it difficult to design targeted preventive interventions, which can identify subjects at risk and prevent persistent opioid use after bariatric surgery. Future studies could imply pharmacokinetic-, pharmacodynamics-, and physiological-based modelling of pain treatment. More attention to social, physiologic, and psychological factors may be warranted in order to identify specific risk profiles of subjects considered for bariatric surgery in order to tailor and optimize current treatment recommendations for this population.

Use of Opioid Analgesics Before and After Gastric Bypass Surgery in Sweden: a Population-Based Study

BACKGROUND

Little is known regarding the use of opioid analgesics among patients who have undergone bariatric surgery. The Roux-en-Y gastric bypass (RYGB) procedure has been shown to significantly increase the rate of absorption of and exposure to morphine, raising concerns regarding the potentially increased risk of side-effects and the development of substance-use disorder.

OBJECTIVES

The aim of this study was to describe the pattern of opioid use over time following RYGB and to see if the pattern differs between patients with a high opioid consumption (HOC) prior to surgery and those with a low consumption (LOC).

SETTING

University Hospital of Örebro, Sweden.

METHODS

The study was a descriptive retrospective population-based cohort study where two registers with complete coverage were cross-matched.

RESULTS

The study population comprised 35,612 persons (1628 HOC, and 33,984 LOC). After surgery, the number of HOC patients increased to 2218. Mean daily opioid consumption in the total population and the LOC group increased after surgery (p < .0005). In the HOC group, there was no difference between mean daily consumption before and after surgery.

CONCLUSION

In this nationwide study, we have showed that there is an increase in consumption of opioid analgesics after gastric bypass surgery in Sweden. The increase in the number of individuals with high opioid consumption in the total population was mainly due to an increase in the group of patients with a low consumption prior to surgery.

Effects of Bariatric Surgery Observed in Postmortem Toxicology Casework

Bariatric surgery has been on the rise and patients often have multiple indications for pre- and post-operative pharmacotherapy. Procedures target the stomach and/or small intestine and affect weight loss through restriction, malabsorption, or a combination of the two. The absorption and/or metabolism of drugs via the gastrointestinal tract could be altered by different mechanisms. Several cases at the North Carolina Office of the Chief Medical Examiner's Toxicology Laboratory (NCOCME) have raised questions about the potential impact of these procedures on the disposition of drugs in the body and how that altered disposition may affect cause and manner of death. Overmedication and postmortem redistribution are not enough to explain the phenomena seen in some NCOCME bariatric surgery-related casework. Case examples include a 46-year-old female with a history of Roux-en-Y gastric bypass (RYGB) who suffered a witnessed collapse. Toxicological findings included elevated concentrations of oxymorphone at 0.49 mg/L in vena cava blood. A 67-year-old female, who died from vomiting and bacterial gastritis one day after placement of two intragastric weight-loss balloons, had elevated concentrations of duloxetine at 1.4 mg/L in the iliac vein blood and 9.3 mg/kg in the liver. Her medication was strictly controlled by her sister and gastric contents were without intact tablets or residue at autopsy.

The influence of bariatric surgery on oral drug bioavailability in patients with obesity: A systematic review

Anatomical changes in the gastrointestinal tract and subsequent weight loss may influence drug disposition and thus drug dosing following bariatric surgery. This review systematically examines the effects of bariatric surgery on drug pharmacokinetics, focusing especially on the mechanisms involved in restricting oral bioavailability. Studies with a longitudinal before-after design investigating the pharmacokinetics of at least one drug were reviewed. The need for dose adjustment following bariatric surgery was examined, as well as the potential for extrapolation to other drugs subjected to coinciding pharmacokinetic mechanisms. A total of 22 original articles and 32 different drugs were assessed. The majority of available data is based on Roux-en-Y gastric bypass (RYGBP) (18 of 22 studies), and hence, the overall interpretation is more or less limited to RYGBP. In the case of the majority of studied drugs, an increased absorption rate was observed early after RYGBP. The effect on systemic exposure allows for a low degree of extrapolation, including between drugs subjected to the same major metabolic and transporter pathways. On the basis of current understanding, predicting the pharmacokinetic change for a specific drug following RYGBP is challenging. Close monitoring of each individual drug is therefore recommended in the early postsurgical phase. Future studies should focus on the long-term effects of bariatric surgery on drug disposition, and they should also aim to disentangle the effects of the surgery itself and the subsequent weight loss.

Plasma concentrations of etonogestrel in women using oral desogestrel before and after Roux-en-Y gastric bypass surgery: a pharmacokinetic study

OBJECTIVE

To investigate whether Roux-en-Y gastric bypass (RYGB) affects oral desogestrel (etonogestrel) pharmacokinetics.

DESIGN

Single centre, open label, phase-2 pharmacokinetic study.

SETTING

University hospital of Linköping, Sweden.

POPULATION

Fourteen women with planned RYGB surgery were included; nine women aged 18-45 years using 75 micrograms desogestrel completed the study.

METHODS

Steady-state etonogestrel pharmacokinetic (PK) parameters were measured on three occasions for each individual (at 8 ± 6 weeks before surgery, and at 12 ± 2 and 52 ± 2 weeks after surgery). Each patient served as her own control. On each occasion, serum samples were collected during a 24-hour period and etonogestrel concentrations were determined with ultra-performance liquid chromatography/tandem mass spectrometry.

MAIN OUTCOME MEASURES

Area under the plasma concentration time curve of etonogestrel (AUC_{0-24 hours} ).

RESULTS

All women had significant postoperative weight loss. There were no significant differences in AUC_{0-24 hours} , terminal half-lives (t_½ ), time to peak serum concentrations (T_max ), or apparent oral clearances of etonogestrel (CL_oral ) before and after gastric bypass surgery on any occasion. Peak serum concentrations (C_max ) increased after 52 ± 2 weeks compared with preoperative values (0.817 ng/ml versus 0.590 ng/ml, P = 0.024).

CONCLUSION

To our knowledge, this is the first study to investigate the effects on desogestrel pharmacokinetics after RYGB. This study did not reveal any clinically significant changes in etonogestrel pharmacokinetics, suggesting that oral desogestrel may be used by women after RYGB surgery. The sample size was limited, however, and therefore the results should be interpreted cautiously.

TWEETABLE ABSTRACT

The pharmacokinetics of oral desogestrel does not appear to change after gastric bypass surgery.

Systematic review of drug bioavailability following gastrointestinal surgery

PURPOSE

Inter- and intraindividual pharmacokinetics variability in humans affects the way in which drugs act on the body. Gastrointestinal surgery has an impact on this variability and significantly alters the kinetics of drugs in post-surgical patients. The way in which pharmacokinetic profiles are modified depends on the type of operative procedure performed. The extent to which the absorption of different groups of drugs is affected varies according to the site and length of intestinal resections.

METHODS

A literature search was conducted based on the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) protocol. Three databases were searched: MEDLINE, Embase, and the Cochrane Library. For each drug, potential changes in absorption were described, including recommendations extracted from the results of the studies and collected according to authors' criteria as practical conclusions, and grades of recommendation were determined by levels of evidence using the Oxford Centre for Evidence-Based Medicine scale.

RESULTS

Sixty-eight articles were collected during the selection process after the bibliographic search. The main outcomes for 60 drugs from the various studies were classified according to each type of surgery.

CONCLUSIONS

Modifications in the digestive tract secondary to gastrointestinal surgery may compromise the bioavailability of drugs. Decreased absorption surface, gastric emptying speed, and gastric pH alteration are factors to be taken into account in the management of pharmacological treatment after surgery. Evidence supported by data in clinical practice is scarce, but after studying the pharmacokinetic profile of some molecules, it is possible to offer recommendations for its adaptation to the patient's clinical situation.

Influence of Morbid Obesity on the Pharmacokinetics of Morphine, Morphine-3-Glucuronide, and Morphine-6-Glucuronide

Introduction

Obesity is associated with many pathophysiological changes that may result in altered drug metabolism. The aim of this study is to investigate the influence of obesity on the pharmacokinetics of morphine, morphine-3-glucuronide (M3G), and morphine-6-glucuronide (M6G) through a combined analysis in morbidly obese patients and non-obese healthy volunteers.

Methods

In this analysis, data from 20 morbidly obese patients [mean body mass index 49.9 kg/m² (range 37.6–78.6 kg/m²) and weight 151.3 kg (range 112–251.9 kg)] and 20 healthy volunteers [mean weight 70.6 kg (range 58–85 kg)] were included. Morbidly obese patients received 10 mg of intravenous (I.V.) morphine after gastric bypass surgery, with additional morphine I.V. doses as needed. Healthy volunteers received an I.V. bolus of morphine of 0.1 mg/kg followed by an infusion of 0.030 mg kg⁻¹ h⁻¹ for 1 h. Population pharmacokinetic modeling was performed using NONMEM 7.2.

Results

In morbidly obese patients, elimination clearance of M3G and M6G was decreased substantially compared with healthy volunteers (p < 0.001). Regarding glucuronidation, only a slight decrease in the formation of M6G and a delay in the formation of M3G was found (both p < 0.001). Obesity was also identified as a covariate for the peripheral volume of distribution of morphine (p < 0.001).

Conclusion

Metabolism of morphine is not altered in morbidly obese patients. However, decreased elimination of both M3G and M6G is evident, resulting in a substantial increase in exposure to these two metabolites. A rational explanation of this finding is that it results from alterations in membrane transporter function and/or expression in the liver.

ClinicalTrials.gov identifier: NCT01097148.

Electronic supplementary material

The online version of this article (doi:10.1007/s40262-017-0544-2) contains supplementary material, which is available to authorized users.

Impact of body weight, low energy diet and gastric bypass on drug bioavailability, cardiovascular risk factors and metabolic biomarkers: protocol for an open, non-randomised, three-armed single centre study (COCKTAIL)

INTRODUCTION

Roux-en-Y gastric bypass (GBP) is associated with changes in cardiometabolic risk factors and bioavailability of drugs, but whether these changes are induced by calorie restriction, the weight loss or surgery per se, remains uncertain. The COCKTAIL study was designed to disentangle the short-term (6 weeks) metabolic and pharmacokinetic effects of GBP and a very low energy diet (VLED) by inducing a similar weight loss in the two groups.

METHODS AND ANALYSIS

This open, non-randomised, three-armed, single-centre study is performed at a tertiary care centre in Norway. It aims to compare the short-term (6 weeks) and long-term (2 years) effects of GBP and VLED on, first, bioavailability and pharmacokinetics (24 hours) of probe drugs and biomarkers and, second, their effects on metabolism, cardiometabolic risk factors and biomarkers. The primary outcomes will be measured as changes in: (1) all six probe drugs by absolute bioavailability area under the curve (AUC_oral/AUC_iv) of midazolam (CYP3A4 probe), systemic exposure (AUC_oral) of digoxin and rosuvastatin and drug:metabolite ratios for omeprazole, losartan and caffeine, levels of endogenous CYP3A biomarkers and genotypic variation, changes in the expression and activity data of the drug-metabolising, drug transport and drug regulatory proteins in biopsies from various organs and (2) body composition, cardiometabolic risk factors and metabolic biomarkers.

ETHICS AND DISSEMINATION

The COCKTAIL protocol was reviewed and approved by the Regional Committee for Medical and Health Research Ethics (Ref: 2013/2379/REK sørøst A). The results will be disseminated to academic and health professional audiences and the public via presentations at conferences, publications in peer-reviewed journals and press releases and provided to all participants.

TRIAL REGISTRATION NUMBER

NCT02386917.

Obesity and drug pharmacology: a review of the influence of obesity on pharmacokinetic and pharmacodynamic parameters

INTRODUCTION

The rising prevalence of obesity confronts clinicians with dosing problems in the (extreme) overweight population. Obesity has a great impact on key organs that play a role in the pharmacokinetics (PK) and pharmacodynamics (PD) of drugs, however the ultimate impact of these changes on how to adapt the dose may not always be known. Areas covered: In this review, physiological changes associated with obesity are discussed. An overview is provided on the alterations in absorption, distribution, drug metabolism and clearance in (morbid) obesity focusing on general principles that can be extracted from pharmacokinetic studies. Also, relevant pharmacodynamic considerations in obesity are discussed. Expert opinion: Over the last two decades, increased knowledge is generated on PK and PD in obesity. Future research should focus on filling in the knowledge gaps that remain, especially in connecting obesity-related physiological changes with changes in PK and/or PD and vice versa. Ultimately, this knowledge can be used to develop physiologically based PK and PD models on the basis of quantitative systems pharmacology principles. Moreover, efforts should focus on thorough prospective evaluation of developed model-based doses with subsequent implementation of these dosing recommendations in clinical practice.

RYGB and Drug Disposition: How to Do Better? Analysis of Pharmacokinetic Studies and Recommendations for Clinical Practice

An important issue in the follow-up of patients with bariatric surgery remains to determine whether their therapeutic management should be different after surgery. In this article, we first reviewed all pharmacokinetic studies involving at least four subjects who underwent the Roux-en-Y gastric bypass (RYGB) bariatric surgery. Twenty-five publications were selected and, overall, 25 drugs were studied. Drug solubility and permeability parameters for each drug were defined using different parameters or classifications. Increased rates of oral drug absorption were predominantly observed. Conversely, drug exposure differed from one drug to another. Considering the galenic formulation and the Biopharmaceutics Classification System (BCS) class may help the prediction of oral drug exposure outcome after RYGB. We propose a strategy aiming to guide prescription and drug monitoring in patients with RYGB. But further research is clearly needed due to the unique characteristics of the bariatric population. Priority should be given to drugs that do not have clinical or biological surrogates for dose adaptation.

Morphine and metabolites plasma levels after administration of sustained release morphine in Roux-en-Y gastric bypass subjects versus matched control subjects

BACKGROUND

Better knowledge of opioid pharmacology after Roux-en-Y gastric bypass (RYGB) is required for optimizing their use in this growing population.

OBJECTIVE

The aim of this case-controlled pharmacokinetic (PK) study was to compare morphine and its glucuronidated metabolites (morphine-3-glucuronide and morphine-6-glucuronide) plasma PKs between patients with RYGB and their controls.

SETTINGS

University hospital, Lariboisière Hospital, Paris.

METHODS

Thirty milligrams of morphine as a sustained-release formulation was orally administered in 12 women who had undergone RYGB for at least 2 years (RYGB group) and in their nonsurgical controls matched for sex, body mass index (±2 points), and age (±5 yr). Morphine, morphine-3-glucuronide, and morphine-6-glucuronide plasma concentrations over a 12-hour period were determined by a validated method using liquid chromatography mass spectrometry in tandem. Drowsiness, respiratory rate, and oxygen saturation were monitored during the PK visit.

RESULTS

Morphine oral area under the curve (for time 0-12 hr; 115.8 ± 108.0 nmol.hr/L and 86.9 ± 38.8 nmol.hr/L for RYGB group and control group, respectively, P = .71), morphine at maximal concentration, metabolites oral area under the curve (for time 0-12 hr)_, and other PK parameters were similar between groups. After drug administration, mean drowsiness was superior in RYGB group. Mean respiratory rate and oxygen saturation were similar in both groups.

CONCLUSION

No dose adjustment seems to be needed for sustained release morphine when prescribed to RYGB patients.

Endogenous Opiates and Behavior: 2015

This paper is the thirty-eighth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2015 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia, stress and social status, tolerance and dependence, learning and memory, eating and drinking, drug abuse and alcohol, sexual activity and hormones, pregnancy, development and endocrinology, mental illness and mood, seizures and neurologic disorders, electrical-related activity and neurophysiology, general activity and locomotion, gastrointestinal, renal and hepatic functions, cardiovascular responses, respiration and thermoregulation, and immunological responses.

Increased intravenous morphine self-administration following Roux-en-Y gastric bypass in dietary obese rats

Roux-en-Y gastric bypass (RYGB) surgery is a commonly performed and very effective method to achieve significant, long-term weight loss. Opioid analgesics are primarily used to manage postoperative pain as fewer alternative medication options are available for bariatric surgery patients than for the general population. Recent clinical studies support a greater risk for substance use following bariatric surgery, including an increased use of opioid medications. The present study is the first to study morphine self-administration in a rat model of RYGB. High fat diet-induced obese (HFD-DIO) rats underwent RYGB (n=14) or sham-surgery with ad libitum HFD (SHAM, n=14) or a restricted amount that resulted in weight matched to the RYGB cohort (SHAM-WM, n=8). An additional normal-diet (ND, n=7), intact (no surgery) group of rats was included. Two months after the surgeries, rats were fitted with jugular catheters and trained on a fixed ratio-2 lick task to obtain morphine intravenously. Both morphine-seeking (number of licks on an empty spout to obtain morphine infusion) and consumption (number of infusion) were significantly greater in RYGB than any control group beginning on day 3 and reached a two-fold increase over a period of two weeks. These findings demonstrate that RYGB increases motivation for taking morphine and that this effect is independent of weight loss. Further research is warranted to reveal the underlying mechanisms and to determine whether increased morphine use represents a risk for opioid addiction following RYGB. Identifying risk factors preoperatively could help with personalized postoperative care to prevent opioid abuse and addiction.