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

Examining the Impact of Diet-and-Exercise-Induced Weight Loss on Drug Metabolism and Gastric Emptying in Patients with Obesity

Obesity significantly influences drug pharmacokinetics (PK), which challenges optimal dosing. This study examines the effects of diet-and-exercise-induced weight loss on key drug-metabolizing enzymes and gastric emptying in patients with obesity, who frequently require medications for comorbidities. Participants followed a structured weight management program promoting weight loss over 3-6 months and were not concomitantly on potential CYP inducers or inhibitors. Using a drug cocktail of acetaminophen, caffeine, omeprazole, and midazolam, we assessed UGT1A1, CYP1A2, CYP2C19, and CYP3A4 enzyme activities before and after weight loss, respectively, by measuring parent and metabolite concentrations. The time to maximum acetaminophen plasma concentrations reflected the gastric emptying time. PK profiles were compared across two phases: baseline (Phase 1) and post-weight loss (Phase 2). Twenty-four participants enrolled, 21 completed Phase 1 and 12 completed both phases. Statistically significant (N = 12, P < .05) gains in CYP2C19 and CYP3A4 activity were observed after weight loss of 7.6% to 26.2%, with a median [25th, 75th percentile] increase in activity of 90.5 [15.0, 194.3] % and 43.0 [7.5, 68.0] %, respectively. A 2- or 3-h single plasma sample-based ratio of the metabolite to parent concentration strongly correlated with the respective AUC ratio for the drug metabolism phenotype (N = 21). Our findings provide provisional data for evaluation of the effects of non-pharmacologically and non-surgically induced weight loss on gastric emptying and drug metabolism for future physiologically based PK models. Development of mechanistic models to optimize drug dosing in obesity are necessary since weight and body composition shifts are expected with emerging new treatments.

Drug absorption from oral formulations in patients with short bowel syndrome: a comprehensive update of the literature

INTRODUCTION

Drug absorption is often altered and typically diminished in patients with short bowel syndrome (SBS). It is important to understand the patient's gastrointestinal anatomy, the absorptive capacity of the remaining bowel, and the physicochemical and pharmacokinetic properties of the drug to optimize oral pharmacotherapy.

AREAS COVERED

The primary focus was to provide an updated understanding of the absorption of various drugs in patients with short bowel syndrome. Forty-seven studies covering 13 different drug classes were included in the review and study details, patient characteristics, drug characteristics and pharmacokinetic findings were summarized for each drug class.

EXPERT OPINION

Improving and simplifying drug treatment in patients with SBS have high priority, but the patients are multi diseased so knowledge regarding absorption of drugs as e.g. antithrombotic agents, immunosuppressants is urgently needed. Therefore, it is crucial to advance our understanding of the fundamental factors involved in drug absorption, spanning from drug design to pathophysiology. With the growing knowledge in drug design and gastrointestinal pathophysiology, we anticipate the development of computer models that can accurately predict optimal absorption in the future.

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.

Obesity and bariatric surgery in kidney transplantation: A clinical review

Obesity is increasing worldwide, and this has major implications in the setting of kidney transplantation. Patients with obesity may have limited access to transplantation and increased posttransplant morbidity and mortality. Most transplant centers incorporate interventions aiming to target obesity in kidney transplant candidates, including dietary education and lifestyle modifications. For those failing nutritional restriction and medical therapy, the use of bariatric surgery may increase the transplant candidacy of patients with obesity and end-stage renal disease (ESRD) and may potentially improve the immediate and late outcomes. Bariatric surgery in ESRD patients is associated with weight loss ranging from 29.8% to 72.8% excess weight loss, with reported mortality and morbidity rates of 2% and 7%, respectively. The most commonly performed bariatric surgical procedures in patients with ESRD and in transplant patients are laparoscopic sleeve gastrectomy (LSG) and laparoscopic Roux-en-Y gastric bypass. However, the correct timing of bariatric surgery and the ideal type of surgery have yet to be determined, although pretransplant LSG seems to be associated with an acceptable risk-benefit profile. We review the impact of obesity on kidney transplant candidates and recipients and in potential living kidney donors, exploring the potential impact of bariatric surgery in addressing obesity in these populations, thereby potentially improving posttransplant outcomes.

Antiseizure Medication use in Gastric Bypass Patients and Other Post-Surgical Malabsorptive States

Healthcare professionals are encountering an increasing number of patients who have undergone bariatric surgeries. Antiseizure medications (ASM) have a narrow therapeutic window, and patients with malabsorptive states receiving ASM present a complex situation as the pharmacokinetics of these drugs have only been studied in patients with a normal functioning gastrointestinal tract. Patients with malabsorptive states may have altered pharmacokinetics, and there is limited literature to guide drug selection and dosage adjustment in patients with malabsorptive states. This review highlights pharmacokinetic parameters of common ASM, and considerations when managing patients on them. The effect of pH, lipophilicity, absorption, and metabolism should be taken into account when selecting and managing ASMs in this patient population. Based on these parameters, levetiracetam, and topiramate have fewer issues referable to absorption related to bariatric surgery while oral formulations of phenytoin, carbamazepine, oxcarbamazepine and valproic acid have reduced absorption due to effects of bariatric surgery based on the pharmacokinetic properties of these medications. Extended formulations should be avoided and ASM serum concentrations should be checked before and after surgery. The care of patients with epilepsy who are scheduled to undergo bariatric surgery should be guided by a multidisciplinary team including a pharmacist and a neurologist who should be involved in the adjustment of the ASMs throughout the pre-surgical and post-surgical periods.

A review of indications and comorbidities in which warfarin may be the preferred oral anticoagulant

WHAT IS KNOWN AND OBJECTIVE

Direct oral anticoagulants (DOACs) are increasingly prescribed instead of warfarin for chronic anticoagulation for ease of dosing, fewer interactions, and less stringent monitoring. However, it is important to consider indications and comorbidities for which warfarin is still the preferred anticoagulant. This review aims to capture these clinical scenarios in which warfarin may still be preferred over DOACs.

METHODS

We undertook a comprehensive literature search using the PubMed database. Key search terms were based on DOAC clinical trial exclusion criteria, as well as indications and conditions in which the use of DOACs for anticoagulation has suggested harm. Society guidelines and tertiary literature were used to inform expert opinion where necessary. Studies were included if they investigated the use of DOACs or warfarin in the identified indications or conditions.

RESULTS AND DISCUSSION

Currently, evidence for the use of warfarin over DOACs for anticoagulation is strongest for patients with prosthetic valves, antiphospholipid syndrome, or a high risk of gastrointestinal bleeding. For several clinical situations, including mitral stenosis, obesity, altered gastrointestinal anatomy, pulmonary arterial hypertension, renal or hepatic impairment, and left ventricular thrombus, evidence is lacking but may eventually support the use of DOACs. Depending on indication and condition, appropriateness of DOAC use may vary by agent.

WHAT IS NEW AND CONCLUSION

New evidence continues to support new indications and conditions in which DOACs may be appropriate to use for anticoagulation. There are key clinical scenarios, however, in which emerging literature continues to support warfarin as the preferred anticoagulant.

Physiologically Based Pharmacokinetic/Pharmacodynamic Modeling to Support Waivers of In Vivo Clinical Studies: Current Status, Challenges, and Opportunities

Physiologically based pharmacokinetic/pharmacodynamic (PBPK/PD) modeling has been extensively applied to quantitatively translate in vitro data, predict the in vivo performance, and ultimately support waivers of in vivo clinical studies. In the area of biopharmaceutics and within the context of model-informed drug discovery and development (MID3), there is a rapidly growing interest in applying verified and validated mechanistic PBPK models to waive in vivo clinical studies. However, the regulatory acceptance of PBPK analyses for biopharmaceutics and oral drug absorption applications, which is also referred to variously as "PBPK absorption modeling" [Zhang et al. CPT: Pharmacometrics Syst. Pharmacol. 2017, 6, 492], "physiologically based absorption modeling", or "physiologically based biopharmaceutics modeling" (PBBM), remains rather low [Kesisoglou et al. J. Pharm. Sci. 2016, 105, 2723] [Heimbach et al. AAPS J. 2019, 21, 29]. Despite considerable progress in the understanding of gastrointestinal (GI) physiology, in vitro biopharmaceutic and in silico tools, PBPK models for oral absorption often suffer from an incomplete understanding of the physiology, overparameterization, and insufficient model validation and/or platform verification, all of which can represent limitations to their translatability and predictive performance. The complex interactions of drug substances and (bioenabling) formulations with the highly dynamic and heterogeneous environment of the GI tract in different age, ethnic, and genetic groups as well as disease states have not been yet fully elucidated, and they deserve further research. Along with advancements in the understanding of GI physiology and refinement of current or development of fully mechanistic in silico tools, we strongly believe that harmonization, interdisciplinary interaction, and enhancement of the translational link between in vitro, in silico, and in vivo will determine the future of PBBM. This Perspective provides an overview of the current status of PBBM, reflects on challenges and knowledge gaps, and discusses future opportunities around PBPK/PD models for oral absorption of small and large molecules to waive in vivo clinical studies.

Effectiveness and Safety of Bariatric Surgery in Patients with End-Stage Chronic Kidney Disease or Kidney Transplant

OBJECTIVE

This study aimed to evaluate (1) the effectiveness, complications, and postoperative access to transplantation in end-stage chronic kidney disease (ECKD) and (2) the effectiveness and complications of bariatric surgery in patients who had already undergone kidney transplant.

METHODS

A systematic review and meta-analysis of mortality and complications rates were performed. Thirty studies were reviewed.

RESULTS

After bariatric surgery, patients with ECKD had similar postoperative weight loss to patients from the general population. Meta-analysis showed post-bariatric surgery rates of 2% (95% CI: 0%-3%) for mortality and 7% (95% CI: 2%-14%) for complications. Approximately one-fifth of the patients had access to a transplant. This rate may be underestimated because of the short duration of follow-up. The lack of control groups did not allow for a conclusion on the role of bariatric surgery in facilitating access to kidney transplantation. In patients who had received a kidney transplant, bariatric surgery seemed to improve renal function but increased graft-rejection risk, possibly because of changes in the bioavailability of immunosuppressant drugs.

CONCLUSIONS

Bariatric surgery yields significant weight loss in patients with ECKD that improves patients' chances of accessing a transplant but does not guarantee it; however, the risk for complications and death is higher than in other patients. After transplantation, bariatric surgery-induced weight loss appeared to positively impact the function of the grafted kidney, but careful monitoring of immunosuppressant medications is required.

Effect of Roux-en-Y gastric bypass on the bioavailability of metoprolol from immediate and controlled release tablets: a single oral dose study before and after surgery

Objective

Roux-en-Y gastric bypass (RYGB) surgery induces major changes in the gastrointestinal tract that may alter the pharmacokinetics of orally administered drugs. Results from pharmacokinetic studies are sparse. This study aimed to investigate the effect of RYGB on the bioavailability of metoprolol from immediate release (IR) and controlled release (CR) tablets in female patient volunteers before and after surgery.

Methods

An explorative, two-phase, single oral dose pharmacokinetic study of metoprolol in female patients undergoing RYGB was carried out. The dose was administered twice in each patient, 1 month before and 6 months after surgery. After intake of either 100 mg of metoprolol IR or CR tablet serum concentration-time profiles of metoprolol were determined. The endpoint was the ratio of AUC_after/AUC_before of metoprolol.

Results

Twelve patients were included in the study (metoprolol IR: 7; metoprolol CR: 5). After intake of a metoprolol IR tablet major intraindividual and interindividual differences for area under the serum concentration versus time curve (AUC) of metoprolol before and after surgery were observed (range ratio AUC_{0-10 hours after}/AUC_{0-10 hours before}: 0.74-1.98). For metoprolol CR tablets a significant reduction in bioavailability of metoprolol was observed after surgery (range ratio AUC_{0-24 hours after}/AUC_{0-24 hours before}: 0.43-0.77).

Conclusion

RYGB may influence the bioavailability of metoprolol from an IR tablet. The magnitude of changes in bioavailability after RYGB requires close monitoring of patients using metoprolol IR tablets and dose adjustment if deemed necessary. RYGB clearly reduces the bioavailability of metoprolol from a CR tablet. After RYGB clinicians may consider to increase the dose according to clinical response.

Modern pharmacological treatment of obese patients

There are many angles to consider in drug treatment of obese patients. On the one hand, some specific weight loss drugs are available, on the other, several drugs are associated with unintentional weight changes. When treating an obese patient for any given disease, several physiological changes may influence the pharmacokinetic properties of the drugs required. Thus, increased body weight may influence the efficacy and safety of some drug treatments. Even more complicated is the situation after weight reduction surgery. Due to the various changes to the gastrointestinal tract induced by the different surgical techniques used, and the dynamic changes in body composition thereafter, drug dosing has to be constantly reconsidered. Whereas all of these issues are of clinical importance, none of them have been investigated in the necessary depth and broadness to ensure safe and efficacious drug treatment of the massively obese patient. Individual considerations have to be based on comorbidities, concomitant medication, and on specific drug properties, for example, lipophilicity, volume of distribution, and metabolism. In this article we summarize the data available on different aspects of drug treatment in the obese patient with the hope of improving patient care.

Longitudinal Impacts of Gastric Bypass Surgery on Pharmacodynamics and Pharmacokinetics of Statins

PURPOSE

Undergoing Roux-en-Y gastric bypass (RYGB) is expected to affect orally administered drug absorption. Statins are commonly prescribed to patients with obesity for the prevention of atherosclerotic cardiovascular diseases by lowering cholesterol. This is the first longitudinal prospective study on impacts of RYGB on weight loss, pharmacodynamics, and pharmacokinetics of atorvastatin, rosuvastatin, and simvastatin, and their active metabolites, up to 1-year post-surgery.

METHODS

Forty-six patients were recruited, five patients on atorvastatin, twelve on rosuvastatin, nine on simvastatin, and twenty on no statin. The concentrations of atorvastatin, rosuvastatin, and simvastatin with their active metabolites were monitored.

RESULTS

Mean plasma concentrations of atorvastatin and metabolites and rosuvastatin normalized by the unit dose [(nM)/(mg/kg)] decreased by 3- to 6-month post-surgery. Conversely, simvastatin and its metabolite concentrations increased up to 6-month post-surgery, then declined to preoperative levels by 1-year post-surgery. The metabolisms of atorvastatin to hydroxyl-metabolites and simvastatin to simvastatin acid were decreased after RYGB. The weight loss and PD outcomes were comparable between statin and non-statin groups suggesting the key impacts were from RYGB. The discontinuation or reduction of dose of atorvastatin or rosuvastatin post-RYGB exhibited rebounds of LDL levels in some subjects, but the rebound was not apparent with patients on simvastatin pre-surgery.

CONCLUSION

Discontinuations of statin dosing post-RYGB require LDL monitoring and reducing the dose to half seems to have better results. Patients on statin treatment post-RYGB should be followed-up closely based on our pharmacokinetic findings, to ensure therapeutic effects of the treatment with minimal adverse effects.

Effect of Roux-en-Y gastric surgery on ciprofloxacin pharmacokinetics: an obvious effect?

PURPOSE

To evaluate pharmacokinetic parameters of ciprofloxacin in patients undergoing Roux-en-Y gastric surgery (RYGS).

METHODS

Controlled, single-dose, open-label study in patients undergoing RYGS. Healthy overweight/obese patients 18-60 years old were included. The assessment was performed once in control patients and three times in case patients (before surgery and 1 and 6 months after surgery). In each visit, the subjects received a single oral dose of ciprofloxacin 500 mg. Venous blood samples were obtained at baseline and 0.5, 1, 1.25, 1.5, 1.75, 2, 2.5, 3, 4, 8 and 14 h after ciprofloxacin intake. Pre- and post-surgery variables were compared using paired ANOVA or the Wilcoxon tests and control vs cases using ANOVA or Mann Whitney. Given the post-surgery change in body weight, the parameters were corrected by dose (mg)/body weight (kg). The analysis was performed using SPSS.

RESULTS

Ciprofloxacin C_max was significantly reduced 1 month after surgery (1840.9 ± 485.2 vs 1589.6 ± 321.8 ng/ml; p = 0.032) but not 6 months after. C_max on the sixth month was lower than C_max in control group (2160.4 ± 408.6 vs 1589.6 ± 321.8 ng/ml; p < 0.001). After correcting by the dose (mg)/patient's body weight, both C_max and AUClast showed significant decrease 1 and 6 months after surgery: C_max, 289.1 ± 65.3 and 263.5 ± 52.1 (ng/ml)/(dose (mg)/weight (kg)) respectively vs 429.3 ± 127.6 (ng/ml)/(dose (mg)/weight (kg)) at baseline; AUC, 1340.6 ± 243.0 and 1299.2 ± 415.4 (h × ng/ml)/(dose (mg)/weight (kg)) respectively vs 1896.7 ± 396.8 (h × ng/ml)/(dose (mg)/weight (kg)) at baseline. C_max 1 month post-surgery showed lower values than the control group (375.4 ± 77.4 vs 263.5 ± 52.1 ng/ml; p < 0.001).

CONCLUSION

Ciprofloxacin absorption is impaired 1 month and 6 months after RYGS. The effect on C_max and AUClast faded on the sixth month due to weight loss. It is no necessary to modify the doses of ciprofloxacin in these patients.

A gastrointestinal simulation system for dissolution of oral solid dosage forms before and after Roux-en-Y gastric bypass

Background

The Roux-en-Y gastric bypass (RYGB) is a bariatric procedure, greatly reducing the stomach size and bypassing the duodenum and proximal jejunum. Hence, RYGB may reduce the absorption and bioavailability of oral medication. For clinical decisions on the use of medication, knowledge of altered modifications in drug disposition is a prerequisite. An in vitro dissolution method for solid oral medications, simulating conditions before and after RYGB, might be a valuable tool to predict the pharmaceutical availability of medicines frequently used by patients after RYGB.

Objectives

To develop a gastrointestinal simulation system (GISS), mimicking conditions before and after RYGB for investigating dissolution characteristics of solid oral medications, and to assess the pharmaceutical availability of metoprolol from immediate-release (IR) and controlled-release (CR) tablets under these conditions.

Methods

With an adjusted, pharmacopoeial paddle dissolution apparatus, the GISS enables variation in parameters which are relevant to drug release in vivo: pH, volume, residence time, osmolality and agitation. Metoprolol tartrate 100 mg IR tablets and metoprolol CR tablets were tested. Release profiles were determined by measuring the concentrations of metoprolol spectrophotometrically.

Results

From IR tablets, under all conditions applied, >85% of metoprolol was released within 25 min. From all tested CR tablets >90% of metoprolol was released after 22 hours.

Conclusions

This GISS is a suitable dissolution system to assess pharmaceutical availability before and after RYGB. In patients who have undergone RYGB, no problems in pharmaceutical availability of metoprolol IR and CR tablets are to be expected. Any changes in response to metoprolol in patients after RYGB should therefore be ascribed to changes in bioavailability.

Warfarin Dose Adjustment After Biliopancreatic Diversion/Duodenal Switch Bariatric Surgery

BACKGROUND

The absorption of drugs and fat-soluble vitamins is impaired after bariatric surgery on which intestinal length and function are altered. In this context, the anticoagulant effect of warfarin is difficult to predict in the postoperative period.

OBJECTIVE

This study aimed at describing the average weekly warfarin dose required to maintain a therapeutic international normalized ratio (INR) before and up to 1 year after sleeve gastrectomy with biliopancreatic diversion and duodenal switch (BPD/DS). Secondary end points included the number of patients requiring a minimal 20% reduction in their weekly dose of warfarin following the BPD/DS.

METHODS

This descriptive and retrospective longitudinal population study included 20 patients using warfarin who underwent BPD/DS. An INR was considered nontherapeutic if it was below or above 15% of the targeted therapeutic range for any given patient.

RESULTS

One month after the surgery, the median weekly dose of warfarin was 55% lower than the preoperative dose ( P < 0.0001). In the 9 patients with full follow-up data, the warfarin dose at 1 year was still 39% lower than the preoperative dose ( P < 0.05). At that time, all patients presented a minimal dose reduction of 20%.

CONCLUSIONS

BPD/DS robustly reduced the requirement of warfarin, which resulted in lower doses after surgery. This persisted over the first year after the surgery, likely because of enhanced sensitivity. The mechanisms for this effect remain multifactorial, and the exact extent of change in dose cannot be predicted.

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.

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 pharmacokinetics of oral ketoprofen in patients after gastric resection

BACKGROUND

Total and partial gastric resection may affect the pharmacokinetics of drugs, especially orally administered a few days after surgery. Ketoprofen is a non-steroidal anti-inflammatory drug (NSAID) broadly used to treat postoperative pain, including patients after gastric resection. The aim of the research was to analyse the pharmacokinetics (PK) of orally administered ketoprofen in patients after gastrectomy.

METHODS

The research was carried out on two groups of patients after total (TG; Roux-Y procedure) and partial (PG; Billroth II procedure) gastrectomy. The patients in group TG (n=15; mean [SD] age 61.86 [14.15] years; and BMI 24.20 [3.73] kg/m²) and group PG (n=5; mean [SD] age 62.40 [16.80] years; and BMI 23.98 [3.45] kg/m²) received ketoprofen in a single oral dose of 100mg. The measurement of ketoprofen plasma concentrations was made by means of the HPLC (high performance liquid chromatography) method.

RESULTS

The PK parameters in group TG and PG were as follows: maximum plasma concentration (C_max), 3.42 [0.99] and 4.66 [0.81] mg/l (p=0.0220); area under the plasma concentration-time curve from zero to infinity (AUC_0-∞), 9.12 [2.78] and 9.17 [2.87] mg×h/ml (p=0.9734); area under the first moment curve from zero to the time of infinity (AUMC_0-∞), 25.95 [8.52] and 26.53 [11.43] mg×h²/l (p=0.9056); time to reach maximum concentration (t_max), 0.47 [0.25] and 0.55 [0.27] h (p=0.5327), respectively.

CONCLUSIONS

Lower concentrations of ketoprofen in patients after gastrectomy suggest that it might be necessary to apply higher dose of the analgesic.

Drug disposition before and after gastric bypass: fenofibrate and posaconazole

AIMS

Roux-en-Y gastric bypass (RYGB) alters the anatomical structure of the gastrointestinal tract, which can result in alterations in drug disposition. The aim of the present study was to evaluate the oral disposition of two compounds belonging to the Biopharmaceutical Classification System Class II - fenofibrate (bile salt-dependent solubility) and posaconazole (gastric pH-dependent dissolution) - before and after RYGB in the same individuals.

METHODS

A single-dose pharmacokinetic study with two model compounds - namely, 67 mg fenofibrate (Lipanthyl®) and 400 mg posaconazole (Noxafil®) - was performed in 12 volunteers pre- and post-RYGB. After oral administration, blood samples were collected at different time points up to 48 h after administration. Plasma concentrations were determined by high-performance liquid chromatography in order to calculate the area under the concentration-time curve up to 48 h (AUC_0-48 h ), the peak plasma concentration (C_max) and the time to reach peak concentration (T_max ).

RESULTS

After administration of fenofibrate, no relevant differences in AUC_0-48 h , C_max and T_max between the pre- and postoperative setting were observed. The geometric mean of the ratio of AUC_0-48 h post/pre-RYGB for fenofibrate was 1.10 [95% confidence interval (CI) 0.87, 1.40; P = 0.40]. For posaconazole, an important decrease in AUC_0-48 h and C_max following RYGB was shown; the geometric mean of the AUC_0-48 h post/pre-RYGB ratio was 0.68 (95% CI 0.48, 0.96; P = 0.03) and the geometric mean of the C_max pre/post-RYGB ratio was 0.60 (95% CI 0.39, 0.94; P = 0.03). The decreased exposure of posaconazole could be explained by the increased gastric pH and accelerated gastric emptying of fluids post-RYGB. No difference for T_max was observed.

CONCLUSIONS

The disposition of fenofibrate was not altered after RYGB, whereas the oral disposition of posaconazole was significantly decreased following RYGB.

Drug disposition and modelling before and after gastric bypass: immediate and controlled-release metoprolol formulations

AIMS

The aim of the present study was to evaluate the disposition of metoprolol after oral administration of an immediate and controlled-release formulation before and after Roux-en-Y gastric bypass (RYGB) surgery in the same individuals and to validate a physiologically based pharmacokinetic (PBPK) model for predicting oral bioavailability following RYGB.

METHODS

A single-dose pharmacokinetic study of metoprolol tartrate 200 mg immediate release and controlled release was performed in 14 volunteers before and 6-8 months after RYGB. The observed data were compared with predicted results from the PBPK modelling and simulation of metoprolol tartrate immediate and controlled-release formulation before and after RYGB.

RESULTS

After administration of metoprolol immediate and controlled release, no statistically significant difference in the observed area under the curve (AUC(0-24 h)) was shown, although a tendency towards an increased oral exposure could be observed as the AUC(0-24 h) was 32.4% [95% confidence interval (CI) 1.36, 63.5] and 55.9% (95% CI 5.73, 106) higher following RYGB for the immediate and controlled-release formulation, respectively. This could be explained by surgery-related weight loss and a reduced presystemic biotransformation in the proximal gastrointestinal tract. The PBPK values predicted by modelling and simulation were similar to the observed data, confirming its validity.

CONCLUSIONS

The disposition of metoprolol from an immediate-release and a controlled-release formulation was not significantly altered after RYGB; there was a tendency to an increase, which was also predicted by PBPK modelling and simulation.

Proximal Roux-en-Y gastric bypass alters drug absorption pattern but not systemic exposure of CYP3A4 and P-glycoprotein substrates

STUDY OBJECTIVES

To evaluate the effect of Roux-en-Y gastric bypass surgery (RYGB) on the pharmacokinetics of midazolam (a CYP3A4 substrate) and digoxin (a P-glycoprotein substrate).

DESIGN

Prospective, nonblinded, longitudinal, single-dose pharmacokinetic study in three phases: presurgery baseline and postoperative assessments at 3 and 12 months.

PATIENTS

Twelve obese patients meeting current standards for bariatric surgery.

MEASUREMENTS AND MAIN RESULTS

At each study visit, patients received a single dose of oral digoxin and midazolam at 8 a.m. Blood samples were collected at regular intervals for 24 hours after dosing. Continuous 12-lead electrocardiogram (EKG), heart rate, blood pressure, and respiratory rate were monitored, and pharmacokinetic parameters from the three visits were compared. The peak plasma concentration (Cmax ) of midazolam increased by 66% and 71% at 3- and 12-month post-RYGB (p=0.017 and p=0.001, respectively), whereas the median time to peak concentration (Tmax ) was reduced by 50%. The mean Cmax for 1'-hydroxymidazolam increased by 87% and 80% at 3 and 12 months (p=0.001 and p<0.001, respectively). However, neither the area under the concentration-time curve (AUC) for midazolam nor the metabolite-to-parent AUC ratio changed significantly over time. For digoxin, the median Tmax decreased from 40 minutes at baseline to 30 and 20 minutes at 3 and 12 months, respectively. The mean AUC for digoxin, heart rate, and EKG patterns were similar across the three study phases.

CONCLUSION

Contemporary proximal RYGB increases the rate of drug absorption without significantly changing the overall exposure to midazolam and digoxin. The Cmax of a CYP3A4 substrate with a high extraction ratio was substantially increased after RYGB.