The effect of morbid obesity on morphine glucuronidation

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.

Medication and supplement pharmacokinetic changes following bariatric surgery: A systematic review and meta-analysis

OBJECTIVES

To evaluate the impact of bariatric surgery on the pharmacokinetic (PK) parameters of orally administered medications and supplements.

METHODS

Systematic searches of bibliographic databases were conducted to identify studies. Pooled effect estimates from different surgical procedures were calculated using a random-effects model.

RESULTS

Quantitative data were synthesized from 58 studies including a total of 1985 participants. Whilst 40 medications and 6 supplements were evaluated across these studies, heterogeneity and missing information reduced the scope of the meta-analysis to the following medications and supplements: atorvastatin, paracetamol, omeprazole, midazolam, vitamin D, calcium, zinc, and iron supplements. There were no significant differences in PK parameters post-surgery for the drugs atorvastatin and omeprazole, and supplements calcium, ferritin, and zinc supplements. Paracetamol showed reduced clearance (mean difference [MD] = -15.56 L/hr, p = 0.0002, I2 = 67%), increased maximal concentration (MD = 6.90 μg/ml, p = 0.006, I2 = 92%) and increased terminal elimination half-life (MD = 0.49 hr, p < 0.0001, I2 = 3%) post-surgery. The remaining 36 medications and 2 supplements were included in a systematic review. Overall, 18 of the 53 drugs and supplements showed post-operative changes in PK parameters.

CONCLUSION

This study demonstrates heterogeneity in practice and could not reach conclusive findings for most PK parameters. Prospective studies are needed to inform best practice and enhance patient healthcare and safety following bariatric surgery.

Morphine for chronic breathlessness in COPD: improvement predictors-cross-sectional study

OBJECTIVE

Morphine is used as palliative treatment of chronic breathlessness in patients with chronic obstructive pulmonary disease (COPD). Part of the patients does not experience a clinically meaningful improvement of breathlessness and it is unclear which characteristics are related to a clinically meaningful improvement of breathlessness after morphine. Therefore, this study assessed whether sensory breathlessness description, demographic and clinical characteristics are related with this improvement.

METHODS

Cross-sectional secondary analysis of the intervention arm of a randomised controlled trial. 45 patients with COPD and moderate-to-very severe chronic breathlessness despite optimal treatment received 20-30 mg oral sustained-release morphine daily for 4 weeks. Using binary logistic regression, the relationship between a clinically meaningful improvement in breathlessness (≥1 point on 0-10 numeric rating scale) and the baseline variables sensory breathlessness descriptors, age, breathlessness and body mass index (BMI) was assessed.

RESULTS

Twenty-one participants (42%) showed a clinically meaningful improvement. Baseline breathlessness (OR 1.51, 95% CI 1.04 to 2.21, p=0.03) and BMI (OR 1.13, 95% 1.02-1.28, p=0.02) were significant associated to a clinically meaningful improvement of breathlessness, while age and sensory breathlessness descriptors were not.

CONCLUSIONS

Worse baseline breathlessness and higher BMI are associated to a clinically meaningful improvement of breathlessness in patients using 20-30 mg oral sustained-release morphine. Opioid treatment should be considered in patients with COPD with severe breathlessness, taking into account the patient's BMI.

The Effect of Upper Extremity Tourniquet Time on Postoperative Pain and Opiate Consumption

BACKGROUND

There is widespread use of pneumatic tourniquet for both upper and lower extremity orthopedic surgeries. Tourniquet use improves visualization, decreases blood loss, and as a result, decreases operative time. Exceeding a certain amount of tourniquet time can cause lasting neuromuscular damage. Orthopedic procedures cause significant pain, and the perioperative narcotic prescriptions after orthopedic surgery have been identified as one of the major contributors to the opioid epidemic. Our aim was to determine whether increasing tourniquet time had a negative impact on immediate postoperative opiate usage in the upper extremity, and to determine other factors associated with increased immediate postoperative opiate usage.

METHODS

A retrospective medical record review was performed on patients who underwent volar pleading for fracture fixation between January 2014 and December 2019 at a single institution. Postoperative pain, morphine equivalent dose (MED) usage, and demographic variables were collected. Multivariable analysis was performed, with P < .05 considered significant.

RESULTS

Immediate postoperative MED consumed was not correlated with operative time, tourniquet time, preoperative substance usage, or sex. However, postoperative MED consumed was correlated with preoperative narcotic use, high body mass index (BMI), and fracture surgery complexity.

CONCLUSIONS

Tourniquet usage under current guidelines does not appear to have an effect on postoperative pain and narcotic usage. Preoperative narcotic usage, BMI, and surgery complexity are significant factors for postoperative opiate consumption.

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.

Intraoperative lidocaine infusion as a sole analgesic agent versus morphine in laparoscopic gastric bypass surgery

Background

The aim of this study was to assess the effect of intra-operative intra-venous (IV) lidocaine infusion compared to IV morphine, on the post-operative pain at rest, the intra-operative and post-operative morphine requirements, the sedation and the Modified Aldrete scores in the post-anesthesia care unit (PACU), the hemodynamic parameters; mean values of the mean blood pressure (MBP) and the heart rate (HR), the peri-operative changes in the SpO2, and the respiratory rate (RR) in laparoscopic Roux-en-y gastric bypass. Sixty patients ˃ 18 years old, with body mass index (BMI) ˃ 35 kg/m2, American Society of Anesthesiologists (ASA) physical status II or III, were randomly divided into 2 groups: the lidocaine (L) group patients received intra-operative IV lidocaine infusion, and the morphine (M) group patients received intra-operative IV morphine.

Results

The post-operative numeric pain rating scale (NPRS) at rest was statistically significant less in group L than in group M patients, in the post-operative 90 min in the PACU. This was reflected on the post-operative morphine requirements in the PACU, as 26.6% of patients in group M required morphine with a mean total dose of 10.8 mg. The mean values of the MBP and HR recorded after intubation were comparable between patients of both groups, indicating attenuation of the stress response to endotracheal intubation by both lidocaine and morphine. However, the mean values of the MBP and HR recorded after extubation were statistically significant lower in patients of group L, indicating the attenuation of the stress response to extubation by lidocaine. Patients in group M showed statistically significant lower mean values of the MBP; before pneumoperitoneum and after 15 min from the pneumoperitoneum, this was reflected on statistically significant higher mean values of the HR. Patients in group L showed statistically significant lower mean values of the MBP and the HR; at 30 and 45 min from the pneumoperitoneum. Patients in group L showed statistically significant lower mean values of the MBP; 60 min from the pneumoperitoneum, after release of pneumoperitoneum and in the PACU. Patients of both groups showed comparable mean values of the HR after 60 min from the pneumoperitoneum, after release of the pneumoperitoneum and in the PACU. No patient in either groups developed post-operative respiratory depression in the PACU. Patients in group L showed statistically significant higher median sedation score, which was reflected on statistically but not clinically significant less Modified Aldrete score in patients of group L.

Conclusions

In morbid obese patients, the intra-operative IV lidocaine infusion offered post-operative analgesia in the PACU, on the expense of a higher sedation score, which didn’t affect the Modified Aldrete score clinically, with attenuation of the stress response to endotracheal intubation and extubation.

Trial registrations

FMASU R16/2021. Registered 1st February 2021, with Clinical Trials Registry (NCT05150756) on 10/08/2021.

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.

Managing the Unpredictable: Mechanistic Analysis and Clinical Recommendations for Lamotrigine Treatment after Bariatric Surgery

Bariatric surgery may alter the absorption and overall bioavailability of oral drugs. Lamotrigine is a major antiepileptic and mood stabilizer, that its use after bariatric surgery has not yet been studied. In this article, we provide a thorough mechanistic analysis of the effects of bariatric surgery on multiple mechanisms important for the absorption, bioavailability and overall pharmacokinetics of lamotrigine. Attributable to its pharmacokinetic properties and drug characteristics, the use of lamotrigine after bariatric surgery may be challenging. The complex situation in which some mechanisms may lead to increased drug exposure (e.g., decreased metabolism, weight loss) while others to its decrease (e.g., hampered dissolution/solubility, decreased gastric volume), may result in lowered, unchanged, or enhanced lamotrigine plasma levels after the surgery. We conclude with a set of clinical recommendations for lamotrigine treatment after bariatric surgery, aiming to allow better patient care, and emphasizing the extra caution that needs to be taken with these patients.

Effect of Roux-en-Y gastric bypass on the pharmacokinetic-pharmacodynamic relationships of liquid and controlled-release formulations of oxycodone

The physiological changes following Roux-en-Y gastric bypass (RYGB) surgery may impact drug release from mechanistically different controlled-release tablets, making generic substitution inappropriate. This study aimed to characterise the pharmacokinetic-pharmacodynamic relationships of oxycodone from a lipid-based and water-swellable controlled-release tablet in RYGB patients. Twenty RYGB patients received 10-mg oral solution oxycodone or 20-mg controlled-release (water-swellable or lipid-based) oxycodone in a three-way, randomised, semiblinded and cross-over study. Blood sampling and pupillary recordings were conducted over a 24-h period. A previously established pharmacokinetic-pharmacodynamic model of these three formulations in healthy volunteers was used in the analysis as a reference model. No differences in absorption kinetics were seen between controlled-release formulations in patients. However, the absorption lag time was 11.5 min in patients vs 14 min in healthy volunteers for controlled-release tablets (P < 0.001). Furthermore, oral bioavailability was 14.4% higher in patients compared to healthy volunteers regardless of formulation type (P < 0.001). Oxycodone pharmacodynamics were not significantly affected by formulation or patient status. However, baseline pupil diameter was inversely correlated with age (P < 0.001) and plasma concentrations of oxycodone at half-maximum effect were 31% lower in males compared to females (P < 0.05). Generic substitution of monophasic lipid-based and water-swellable controlled-release oxycodone tablets may be considered safe in RYGB patients.

How Does Fat Mass Change in the First Year After Bariatric Surgery? A Systemic Review and Meta-Analysis

This systematic review and meta-analysis investigated the time-course effect of different type of bariatric surgeries (BS) up to 1 year post-surgery on fat mass (FM) and body fat percentage (BFP) in patients with morbid obesity. We searched PubMed, Scopus, EMBASE, ISI web of science, and Cochrane databases from October 2002 until May 2020 with no restriction in the English language, to find studies examining the effect of BS on FM (kg) and BFP (%) in morbid obese patients. Meta-analysis of 103 studies carried out on data of 18,166 and 14,575 morbid obese patients following BS, showed that BS was associated with a substantial decrease in FM and BFP, respectively, in 1 month (- 8.17 kg [95% CI - 9.07, - 7.27] and - 1.51% [95% CI - 2.56, - 0.46]), 3 months (- 15.75 [95% CI - 17.49, - 14.0] and - 4.90 [95% CI - 5.97, - 3.83]), 6 months (- 22.51 [95% CI - 23.93, - 21.09] and - 8.56% [95% CI - 9.63, - 7.49]), and 12 months (- 29.69 [95% CI - 31.3, - 28.09] and - 13.49% [95% CI - 14.52, - 12.40]) after the surgery. In conclusion, BS was associated with sustained declines in FM and BFP, from 1 to 12 months, with no indication of plateau phase post-surgery post-operatively. The present study emphasizes that post-bariatric care should have more focus on FM loss during 1-year post-surgery to identify the patients at risk for fat loss plateau.

Oral drug dosing following bariatric surgery: General concepts and specific dosing advice

Bariatric or weight‐loss surgery is a popular option for weight reduction. Depending on the surgical procedure, gastric changes like decreased transit time and volume and increased pH, decreased absorption surface in the small intestine, decreased exposure to bile acids and enterohepatic circulation, and decreased gastrointestinal transit time may be expected. In the years after bariatric surgery, patients will also substantially lose weight. As a result of these changes, the absorption, distribution, metabolism and/or elimination of drugs may be altered. The purpose of this article is to report the general influence of bariatric surgery on oral drug absorption, and to provide guidance for dosing of commonly used drugs in this special population. Upon oral drug administration, the time to maximum concentration is often earlier and this concentration may be higher with less consistent effects on trough concentrations and exposure. Additionally, prescription of liquid formulations to bariatric patients is supported by some reports, even though the high sugar load of these suspensions may be of concern. Studies on extended‐release medications result in an unaltered exposure for a substantial number of drugs. Also, studies evaluating the influence of timing after surgery show dynamic absorption profiles. Although for this group specific advice can be proposed for many drugs, we conclude that there is insufficient evidence for general advice for oral drug therapy after bariatric surgery, implying that a risk assessment on a case‐by‐case basis is required for each drug.

Implications for body weight extremes in solid organ transplantation

The pharmacokinetic profiles of medications are altered in overweight and underweight patients, but few studies have described these differences in patients with body mass index extremes. As solid organ transplant programs expand their candidate selection criteria to accommodate a growing population of patients with weight extremes, it has become imperative to understand and evaluate the impact weight extremes have on the pharmacokinetics of life-sustaining immunosuppression in this population. This review will describe pharmacokinetic and dosing considerations for weight extremes in solid organ transplant recipients, including changes following bariatric surgeries, non-pharmacologic and pharmacologic management strategies for weight loss and gain, and potential drug-drug interactions with popular weight management products.

Prospective study of the changes in pharmacokinetics of immunosuppressive medications after laparoscopic sleeve gastrectomy

Laparoscopic sleeve gastrectomy induces weight loss via the creation of a restrictive gastric tube for early satiety and is associated with an accelerated gastric transit time. A prospective, single-dose pharmacokinetic study was performed, prior to and after laparoscopic sleeve gastrectomy, for tacrolimus, extended-release tacrolimus, mycophenolate mofetil, and enteric-coated mycophenolate sodium. The study included 12 morbidly obese patients in chronic renal failure. The median decrease in body mass index was 8.8 kg/m² with an excess body weight loss of 54.9%. The AUC₂₄ of all drugs were increased after laparoscopic sleeve gastrectomy by 46%, 55%, 77%, and 74%, respectively. The maximum concentrations were increased for tacrolimus, extended-release tacrolimus, and mycophenolate mofetil by 43%, 46%, and 65%. The apparent total clearances were decreased for tacrolimus, mycophenolate mofetil, and enteric-coated mycophenolate sodium by 36%, 57%, and 38%. Laparoscopic sleeve gastrectomy can be associated with significant changes in pharmacokinetics of the drugs evaluated. The mechanism is likely decreased apparent drug clearance due to an increased drug exposure (from a more distal site of intestinal absorption with decreased intestinal metabolism), or decreased clearance (liver metabolism). Adapting the monitoring of immunosuppression will be important to avoid overdosing and potential side effects.

Endogenous opiates and behavior: 2017

This paper is the fortieth consecutive installment of the annual anthological review of research concerning the endogenous opioid system, summarizing articles published during 2017 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides and receptors as well as effects of opioid/opiate agonists and antagonists. The review is subdivided into the following specific topics: molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors (1), the roles of these opioid peptides and receptors in pain and analgesia in animals (2) and humans (3), opioid-sensitive and opioid-insensitive effects of nonopioid analgesics (4), opioid peptide and receptor involvement in tolerance and dependence (5), stress and social status (6), learning and memory (7), eating and drinking (8), drug abuse and alcohol (9), sexual activity and hormones, pregnancy, development and endocrinology (10), mental illness and mood (11), seizures and neurologic disorders (12), electrical-related activity and neurophysiology (13), general activity and locomotion (14), gastrointestinal, renal and hepatic functions (15), cardiovascular responses (16), respiration and thermoregulation (17), and immunological responses (18).

Increased Paracetamol Bioavailability after Sleeve Gastrectomy: A Crossover Pre- vs. Post-Operative Clinical Trial

Oral drug bioavailability may be significantly altered after laparoscopic sleeve gastrectomy (LSG), the most popular bariatric procedure worldwide. Paracetamol (acetaminophen) is the post-bariatric analgesic/antipyretic drug of choice. In this work we studied and analyzed the LSG effects on systemic bioavailability and pharmacokinetics of paracetamol after oral administration of solid vs. liquid dosage form. A 4-armed, pharmacokinetic, crossover trial was performed in patients enrolled for LSG. Single paracetamol dose (500 mg), as caplet (n = 7) or syrup (n = 5), was administered before vs. 4–6 months post-LSG. Bioavailability was enhanced after LSG; in the caplet groups, average AUC_0–t increased from 9.1 to 18.6 µg·h/mL with AUC_0–t difference of 9.5 µg·h/mL (95% CI 4.6–14.5, p = 0.003). C_max increased from 1.8 (95% CI 1.2–2.5) to 4.2 µg/mL (3.6–4.8) after LSG (p = 0.032). In the syrup groups, AUC_0–t increased from 13.4 to 25.6 µg·h/mL, with AUC_0–t difference of 12.2 µg·h/mL (95% CI 0.9–23.5, p = 0.049). C_max changed from 5.4 (95% CI 2.5–8.4) to 7.8 µg/mL (6.1–9.6), and systemic bioavailability was complete (102%) after the surgery. Overall, decreased paracetamol exposure in obesity, with recovery to normal drug levels (caplet) or even higher (syrup) post-LSG, was revealed. In conclusion, attention to paracetamol effectiveness/safety in obesity, and after bariatric surgery, is prudent.

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.

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.

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.