Trends in oral drug bioavailability following bariatric surgery: examining the variable extent of impact on exposure of different drug classes

Clinical Guidance for Dosing and Monitoring Oral Antihormonal Drugs in Patients with Breast Cancer After Roux-en-Y Gastric Bypass

ABSTRACT

Obesity is associated with an increased risk of cancers, such as breast cancer. Roux-en-Y gastric bypass (RYGB) is a common surgical intervention used to induce weight loss, reduce comorbidities, and improve overall survival. Due to alterations in the gastrointestinal tract, RYGB is associated with changes in oral drug disposition, which can affect treatment outcomes. Oral antihormonal agents were monitored in 9 patients who previously underwent RYGB. The results of therapeutic drug monitoring and estradiol concentrations were analyzed, and a review of the relevant literature was performed. As only 1 of the 6 patients prescribed tamoxifen achieved a therapeutic endoxifen concentration with the standard dose of 20 mg/d, a higher starting dose of 40 mg/d was recommended to increase the probability of attaining a therapeutic plasma concentration. All patients with decreased CYP2D6 metabolic activity could not achieve therapeutic plasma concentrations; therefore, CYP2D6 genotyping was recommended before the initiation of tamoxifen therapy to identify patients who should be switched to aromatase inhibitors. Anastrozole and letrozole exposure in patients who underwent RYGB patients appeared sufficient, with no dose adjustment required. However, until more data become available, monitoring aromatase inhibitor efficacy is recommended. Monitoring the drug concentrations is a viable option; however, only indicative data on therapeutic drug monitoring are available. Therefore, estradiol concentrations should be measured.

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.

[Bariatric surgery and drugs: Review of the literature and Adverse Drug Reactions analysis in French National Pharmacovigilance Database]

INTRODUCTION

Bariatric surgery is the only treatment for severe obesity (BMI>35kg/m2) currently recognized as effective both in achieving tangible and lasting weight loss, and in improving obesity-related comorbidities such as type 2 diabetes, hypertension, and cardiovascular complications. Bariatric surgery, like any other surgery of the digestive tract, can have an impact on nutrient absorption, as well as on drug absorption. The literature on drug management in bariatric surgery patients concerned mainly of case reports and retrospective studies involving a small number of patients. No official guidelines are available.

METHODS

We conducted a literature search on the consequences of bariatric surgery in terms of drug bioavailability and/or effect. The Medline® (PubMed) database was searched using the following keywords: "bariatric surgery", "bioavailability", "gastric bypass", and "obesity". We completed this review with an analysis of reports of adverse drug reactions (ADRs) in post-bariatric surgery patients for obesity registered in the National pharmacovigilance database (PVDB). We selected all cases with the mention of "bariatric surgery and/or gastrectomy" as "medical history". After reading the cases, we excluded those in which the patient had undergone surgery for an indication other than obesity, where the route of administration was other than oral, and cases in which ADRs resulted from voluntary overdose, attempted suicide, allergy, switch to Levothyrox® new formulation, meningioma under progestative drugs, inefficacy related to generic substitution and medication error.

RESULTS

The literature search identified mainly "case report" about the impact of bariatric surgery on so-called "narrow therapeutic window" drugs. We identified 66 informative cases out of a total of 565 cases selected (11%) in the PVDB. Nevertheless, the information does not allow a clear relationship between the occurrence of the ADR and the influence of bariatric surgery.

CONCLUSION

There is a lack of official information and/or recommendations on medication use in subjects who have undergone bariatric surgery. Apart from under-reporting, ADRs reports remain largely uninformative. Health professional and patients would be awareness for improving, quantitatively and qualitatively the reporting of ADRs in this population.

PBPK Modeling of Azithromycin Systemic Exposure in a Roux-en-Y Gastric Bypass Surgery Patient Population

In this investigation, PBPK modeling using the Simcyp® Simulator was performed to evaluate whether Roux-en-Y gastric bypass (RYGB) surgery impacts the oral absorption and bioavailability of azithromycin. An RYGB surgery patient population was adapted from the published literature and verified using the same probe medications, atorvastatin and midazolam. Next, a PBPK model of azithromycin was constructed to simulate changes in systemic drug exposure after the administration of different oral formulations (tablet, suspension) to patients pre- and post-RYGB surgery using the developed and verified population model. Clinically observed changes in azithromycin systemic exposure post-surgery following oral administration (single-dose tablet formulation) were captured using PBPK modeling based on the comparison of model-predicted exposure metrics (Cmax, AUC) to published clinical data. Model simulations predicted a 30% reduction in steady-state AUC after surgery for three- and five-day multiple dose regimens of an azithromycin tablet formulation. The relative bioavailability of a suspension formulation was 1.5-fold higher than the tablet formulation after multiple dosing. The changes in systemic exposure observed after surgery were used to evaluate the clinical efficacy of azithromycin against two of the most common pathogens causing community acquired pneumonia based on the corresponding AUC24/MIC pharmacodynamic endpoint. The results suggest lower bioavailability of the tablet formulation post-surgery may impact clinical efficacy. Overall, the research demonstrates the potential of a PBPK modeling approach as a framework to optimize oral drug therapy in patients post-RYGB surgery.

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.

Altered Bioavailability and Pharmacokinetics in Crohn's Disease: Capturing Systems Parameters for PBPK to Assist with Predicting the Fate of Orally Administered Drugs

Backgrond and Objective

Crohn’s disease (CD) is a chronic inflammatory bowel disease that affects a wide age range. Hence, CD patients receive a variety of drugs over their life beyond those used for CD itself. The changes to the integrity of the intestine and its drug metabolising enzymes and transporters (DMETs) can alter the oral bioavailability of drugs. However, there are other changes in systems parameters determining the fate of drugs in CD, and understanding these is essential for dose adjustment in patients with CD.

Methods

The current analysis gathered all the available clinical data on the kinetics of drugs in CD (by March 2021), focusing on orally administered small molecule drugs. A meta-analysis of the systems parameters affecting oral drug pharmacokinetics was conducted. The systems information gathered on intestine, liver and blood proteins and other physiological parameters was incorporated into a physiologically based pharmacokinetic (PBPK) platform to create a virtual population of CD patients, with a view for guiding dose adjustment in the absence of clinical data in CD.

Results

There were no uniform trends in the reported changes in reported oral bioavailability. The nature of the drug as well as the formulation affected the direction and magnitude of variation in kinetics in CD patients relative to healthy volunteers. Even for the same drug, the reported changes in exposure varied, possibly due to a lack of distinction between the activity states of CD. The highest alteration was seen with S-verapamil and midazolam, 8.7- and 5.3-fold greater exposure, respectively, in active CD patients relative to healthy volunteers. Only one report was available on liver DMETs in CD, and indicated reduced CYP3A4 activity. In a number of reports, mRNA expression of DMETs in the ileum and colon of CD patients was measured, focussing on P-glycoprotein (p-gp) transporter and CYP3A4 enzyme, and showed contradictory results. No data were available on protein expression in duodenum and jejunum despite their dominant role in oral drug absorption.

Conclusion

There are currently inadequate dedicated clinical or quantitative proteomic studies in CD to enable predictive PBPK models with high confidence and adequate verification. The PBPK models for CD with the available systems parameters were able to capture the major physiological influencers and the gaps to be filled by future research. Quantification of DMETs in the intestine and the liver in CD is warranted, alongside well-defined clinical drug disposition studies with a number of index drugs as biomarkers of changes in DMETs in these patients, to avoid large-scale dedicated studies for every drug to determine the effects of disease on the drug’s metabolism and disposition and the consequential safety and therapeutic concerns.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40262-022-01169-4.

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 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.

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.

Meta-Analysis of Food Effect on Oral Absorption of Efflux Transporter Substrate Drugs: Does Delayed Gastric Emptying Influence Drug Transport Kinetics?

The oral route of drug administration is the most convenient method of drug delivery, but it is associated with variable bioavailability. Food is one of the major factors that affect oral drug absorption by influencing drug properties (e.g., solubility and dissolution rate) and physiological factors (e.g., metabolism and transport across the gastrointestinal tract). The aim of this work was to investigate the effect of food on the high-affinity intestinal efflux transporter substrate drugs. We hypothesized that transport efficiency is higher in the fed state as compared to the fasted state because of the lower intestinal lumen drug concentration due to prolonged gastric emptying time. A systematic analysis of reported clinical food-effect (FE) studies on 311 drugs was performed and the association of the efflux transport efficiency was investigated on the FE magnitude, i.e., changes in maximal plasma concentration and area under the plasma concentration-time profile curve for both solubility and permeability-limited drugs. In total, 124 and 88 drugs showed positive and negative FE, respectively, whereas 99 showed no FE. As expected, the solubility-limited drugs showed positive FE, but interestingly, drugs with a high potential for efflux transport, were associated with negative FE. Moreover, a high-fat diet was associated with a higher magnitude of negative FE for high-affinity efflux transporter substrates as compared to a low-fat diet. To account for changes in drug absorption after food intake, the prolonged gastric emptying time should be considered in the physiologically based pharmacokinetic (PBPK) modeling of orally absorbed efflux transporter substrate drugs.

Evaluation of An Inpatient Pharmacy Consult on Discharge Medications in Bariatric Surgery Patients

PURPOSE

To evaluate the impact of an inpatient pharmacy consult on discharge medications following bariatric surgery.

METHODS

A pharmacy consult for discharge medication review for bariatric surgery patients was instituted at an academic medical center. The intervention included conducting a medication history, reviewing home medications for updates post-bariatric surgery, creating and documenting a discharge medication plan, and providing patient education. The impact of the intervention was evaluated by comparing medication classes, doses, and formulations prescribed during the intervention relative to a historical control group.

RESULTS

The study included 85 patients who received pharmacist intervention and 167 patients who did not receive pharmacist intervention following bariatric surgery. The prescription of an extended-release medication at discharge in the intervention group was reduced by 19.3% (28.7% vs. 9.4%, p = 0.0005). For patients on hypertension medications, 94.0% had their regimen reduced in the intervention group compared with 37.5% of patients in the control group (p < 0.001). Of patients on insulin at baseline, 87.5% of patients in the intervention group had dose reductions at discharge vs. 66.7% of patients in the control group (p = 0.37). No patients in the intervention group were discharged with oral antihyperglycemic medications or non-insulin injectable medications vs. 33.3% (p = 0.12) and 20.0% (p = 0.47), respectively, in the control group. Readmission rates at 30 days were insignificantly lower in the intervention group (3.5% vs. 4.2%, p = 1).

CONCLUSIONS

Clinical pharmacist involvement in the discharge medication reconciliation process for bariatric surgery patients reduced prescribing of unadjusted medication classes, doses, and drug formulations.

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.

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.

Adaptations in gastrointestinal physiology after sleeve gastrectomy and Roux-en-Y gastric bypass

Linked to the growing obesity epidemic, demand for bariatric and metabolic surgery has increased, the most common procedures being sleeve gastrectomy and Roux-en-Y gastric bypass. Originally, bariatric procedures were described as purely restrictive, malabsorptive, or combined restrictive-malabsorptive procedures limiting food intake, nutrient absorption, or both. Nowadays, anatomical alterations are known to affect gastrointestinal physiology, which in turn affects the digestion and absorption of nutrients and drugs. Therefore, understanding gastrointestinal physiology is crucial to prevent postoperative nutritional deficiencies and to optimise postoperative drug therapy. Preclinical and clinical research indicates that sleeve gastrectomy accelerates liquid and solid gastric emptying and small intestinal transit, and increases bile acid serum levels, whereas its effects on gastrointestinal acidity, gastric and pancreatic secretions, surface area, and colonic transit remain largely unknown. Roux-en-Y gastric bypass diminishes gastric acid secretion, accelerates liquid gastric emptying, and increases bile acid serum levels, but its effects on intestinal pH, solid gastric emptying, intestinal transit time, gastric enzyme secretions, and surface area remain largely unknown. In this Review, we summarise current knowledge of the effects of these two procedures on gastrointestinal physiology and assess the knowledge gaps.

Refractoriness to drugs in migraine may be the result of developing anti-drug antibodies

INTRODUCTION

Migraine is a common neurological disease and is listed second among the most disabling health conditions worldwide. Refractory migraine (RM) is a term used to emphasize the unresponsiveness of migraine to various treatment options, encompassing both episodic refractory and chronic refractory migraine. In this paper we discuss various known and possible mechanisms of pharmacological refractoriness in RM, such as possible involvement of the gut microbiome, the blood-brain barrier, migraine genetics and various mechanisms of pharmacokinetic and pharmacodynamic tolerance. Development of medication-overuse headache as a secondary disorder following migraine is also considered. We argue that the available literature is insufficient to fully explain the mechanisms of refractoriness and we present our hypothesis.

HYPOTHESIS

Refractoriness to drugs in migraine may be the result of developing anti-drug antibodies. Most migraine drugs are small molecules, which cannot elicit an immune response on their own due to their size. However, such molecules can bind to peptide carriers in their vicinity, greatly increasing their immunogenicity. A small molecule possessing this binding ability is called a hapten. Haptens form hapten-carrier complexes (HCCs), which can evoke powerful immune responses. Immune reactions to HCCs are known to be predominantly 'drug allergies' or type 1 drug hypersensitivity reactions', usually resulting from IgE or non-IgE mediated mast cell degranulation. We argue that the immune reaction to HCCs can take shape in developing neutralizing anti-drug antibodies (ADA) in the form of IgG and IgA class antibodies. Since biological therapeutics, such as various monoclonal antibodies, face the issue of ADA-induced drug tolerance, HCCs, being similar in the sense that they carry peptide antigens, are of sufficient size and may be considerably immunogenic, can be responded to in a similar way by producing neutralizing ADA. Furthermore, we argue that such responses are expected to happen more frequently than is thought, due to IgG and IgA being prevalent antibodies, which utilize their neutralizing capabilities on regular basis. Finally, it is important to consider that neutralization reactions in normal immune responses are typically asymptomatic, with the only clinical expression being progressive drug tolerance. These cases may be overshadowed by the life-threatening cases of drug allergy induced anaphylaxis, possibly leading to neutralization reactions being underrecognized.

DISCUSSION

This hypothesis aims to stimulate more research regarding drug resistance, and if it receives support from empirical evidence, it may help further elucidate the mechanisms underlying refractory diseases and contribute to the development of more effective treatment of many disorders.

Treatment of COVID-19 Patients Post-Bariatric Surgery: Issues for Consideration

As COVID-19 has been expanding rapidly around the world, the types of patients and their backgrounds vary. The substantially altered GI anatomy/physiology after bariatric surgery presents new challenges to the field of oral drug therapy. In this report we highlight issues for consideration when treating COVID-19 patients who previously underwent bariatric surgery and provide practical tools to allow optimal care of these patients. Post-bariatric absorption/pharmacokinetic changes may warrant dose adjustment, as well as the use of liquid oral dosage forms or parenteral routes of administration, if available. Realizing the potentially altered pharmacokinetics of various drugs after bariatric surgery is essential for providing optimal pharmacological therapy and overall patient care.

Physiologically-Based Pharmacokinetic Model on the Oral Drug Absorption in Roux-en-Y Gastric Bypass Bariatric Patients: Amoxicillin Tablet and Suspension

The potential of a physiologically-based pharmacokinetic (PBPK) model to predict oral amoxicillin bioavailability, by considering the physiological changes after "Roux-en-Y gastric bypass" (RYGB) surgery in bariatric patients, was evaluated. A middle-out approach for parameter estimations was undertaken using in vitro, in situ, and in vivo data. The observed versus predicted plasma concentrations and the model sensitivity of the simulated parameters of AUC_0-inf and C_max of amoxicillin (AMX) were used to confirm the reliability of the estimation. The model considers that a drug-transporter (Transp) in the initial segments of the normal intestine plays a significant role in the AMX absorption. A lower fraction absorbed (F_abs) was observed in RYGB patients (54.43% for suspension and 45.21% for tablets) compared to healthy subjects (77.48% capsule). Furthermore, the tablet formulation presented a lower dissolved fraction (F_d) and F_abs compared to the suspension formulation of AMX in RYGB patients (91.70% and 45.21% versus 99.92% and 54.43%, respectively). The AUC_0-inf and C_max were sensitive to changes in R_tintestine, Peff_AMX, and Transp for both healthy and RYGB models. Additionally, AUC_0-inf and C_max were also sensitive to changes in the t_lag parameter for tablet formulation in RYGB patients. The PBPK model showed a reduction in AMX bioavailability as a consequence of reduced intestinal length after RYGB surgery. Additionally, the difference in the predicted F_d and F_abs between suspension and tablet suggests that liquid formulations are preferable in postbariatric patients.

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.

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.

Transjugular Intrahepatic Portosystemic Shunt: A Possible Risk Factor for Direct-Acting Antiviral Treatment Failure in Patients With Hepatitis C?

Direct‐acting antiviral (DAA) therapies have revolutionized the treatment of chronic hepatitis C virus infection, achieving sustained virological response (SVR) rates of >90% even in patients with advanced liver cirrhosis. Having observed an unusual case of repeated DAA therapy failures in a patient with a transjugular intrahepatic portosystemic shunt (TIPS), we assessed a possible association between prior TIPS placement and DAA failure. A structured search of our clinical database revealed 10 patients who had received DAA therapy after TIPS placement. At the time of therapy, most patients (8; 80%) presented with a Child‐Pugh score B, and the following DAA regimens were used: sofosbuvir/ledipasvir ± ribavirin (5 patients), sofosbuvir/daclatasvir ± ribavirin (3), sofosbuvir/velpatasvir (2), and sofosbuvir/velpatasvir/voxilaprevir (1). In total, 5 patients (50%) achieved an SVR, whereas a virological relapse occurred in the other half of the cases, including 2 patients with multiple relapses. In this patient cohort, SVR rates were unusually low for all regimens: sofosbuvir/ledipasvir ± ribavirin, 3/5 (60%); sofosbuvir/daclatasvir ± ribavirin, 2/3 (66%); sofosbuvir/velpatasvir, 0/2 (0%); and sofosbuvir/velpatasvir/voxilaprevir, 0/1 (0%), and patients with a TIPS made up a relevant proportion of DAA failures in patients with cirrhosis at our center: sofosbuvir/ledipasvir, 2/18 (11%); sofosbuvir/daclatasvir, 1/4 (25%); sofosbuvir/velpatasvir, 2/3 (66%); and sofosbuvir/velpatasvir/voxilaprevir, 1/1 (100%). Conclusion: We observed a high rate of virological relapse in patients with a TIPS who received DAA treatment and therefore postulate that TIPS placement may be a possible risk factor for DAA failure due to the profound hemodynamic changes evoked by the intervention. Longer treatment duration or addition of ribavirin might be warranted in these patients.

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.

All disease begins in the gut: Influence of gastrointestinal disorders and surgery on oral drug performance

The term "disease" conjures a plethora of graphic imagery for many, and the use of drugs to combat symptoms and treat underlying pathology is at the core of modern medicine. However, the effects of the various gastrointestinal diseases, infections, co-morbidities and the impact of gastrointestinal surgery on the pharmacokinetic and pharmacodynamic behaviour of drugs have been largely overlooked. The better elucidation of disease pathology and the role of underlying cellular and molecular mechanisms have increased our knowledge as far as diagnoses and prognoses are concerned. In addition, the recent advances in our understanding of the intestinal microbiome have linked the composition and function of gut microbiota to disease predisposition and development. This knowledge, however, applies less so in the context of drug absorption and distribution for orally administered dosage forms. Here, we revisit and re-evaluate the influence of a portfolio of gastrointestinal diseases and surgical effects on the functionality of the gastrointestinal tract, their implications for drug delivery and attempt to uncover significant links for clinical practice.

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.

Omeprazole Absorption and Fasting Gastrinemia After Roux-en-Y Gastric Bypass

PURPOSE

Roux-en-Y gastric bypass (RYGB) is one of the bariatric surgeries most frequently performed worldwide. Since this operation may predispose to the formation of peptic ulcer of the gastrojejunal anastomosis, the use of proton pump inhibitors (PPI) is recommended during the first postoperative year. However, so far, there is no detailed knowledge about the absorption of this medication during the immediate postoperative period and consequently about its effectiveness in blocking acid secretion. The objective was to assess the possible endoscopic peptic changes, the absorption of omeprazole (OME), and the status of fasting gastrinemia before and after RYGB operation.

MATERIALS AND METHODS

OME absorption, the production of its metabolites omeprazole sulfone (OMES) and 5-hydroxyomeprazole (HOME), and basal (fasting) gastrinemia were determined in patients submitted to RYGB before and 2 months after the operation. Upper digestive endoscopy (UDE) was also performed before and 6 months after the operation.

RESULTS

Twenty patients were studied. Preoperatively, all these patients had some peptic changes and 55% tested positive for Helicobacter pylori. Six months after surgery, ten patients still showed endoscopic changes and one patient tested positive for H. pylori. During the postoperative period, there was a reduction of OME absorption and of the production of its metabolites 90 min after administration of the drug, and reduction of serum gastrin levels.

CONCLUSION

The standard OME dose (40 mg) administered after bariatric surgery is insufficient to achieve serum levels that can effectively block the production of hydrochloric acid, permitting the formation of peptic injuries in many patients.

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.

Oral drug therapy following bariatric surgery: an overview of fundamentals, literature and clinical recommendations

Bariatric surgery is the most effective solution for severe obesity and obesity with comorbidities, and the number of patients going through bariatric surgery is rapidly and constantly growing. The modified gastrointestinal anatomy of the patient may lead to significant pharmacokinetic alterations in the oral absorption of drugs after the surgery; however, because of insufficient available literature and inadequate awareness of the medical team, bariatric surgery patients may be discharged from the hospital with insufficient instructions regarding their medication therapy. In this article, we aim to present the various mechanisms by which bariatric surgery may influence oral drug absorption, to provide an overview of the currently available literature on the subject, and to draw guidelines for the recommendations bariatric surgery patients should be instructed before leaving the hospital. To date, and until more robust data are published, it is essential to follow and monitor patients closely for safety and efficacy of their medication therapies, both in the immediate and distant time post-surgery.

Long-term pharmacotherapy considerations in the bariatric surgery patient

PURPOSE

Pharmacists' role in optimizing long-term pharmacotherapy for bariatric surgery patients is detailed.

SUMMARY

Bariatric surgery patients provide a difficult challenge in terms of many pharmacotherapy issues, especially in the chronic care setting, where data on long-term effects of bariatric surgery are limited. The most common procedures are Roux-en-Y gastric bypass (RYGB), adjustable gastric banding, and sleeve gastrectomy. Sleeve gastrectomy has become the most common procedure in the United States, primarily because it has less overall chronic malabsorption effects than RYGB. Pharmacotherapy management is complicated by rapid weight loss combined with a number of pharmacokinetic changes, such as decreased absorption of some medications due to altered gastrointestinal tract anatomy and potentially increased concentrations of some medications due to a decreased volume of distribution resulting from weight loss. Nutritional and metabolic supplementation are of the utmost importance in order to limit deficiencies that can lead to a number of conditions. Many chronic diseases, including hypertension, diabetes, gastroesophageal reflux disease, and urinary incontinence, are improved by bariatric surgery but require close monitoring to ensure the effectiveness of maintenance pharmacotherapy and avoidance of adverse effects. Psychotropic medication management is also an important pharmacotherapy concern, as evidenced by antidepressants being the most commonly used medication class among preoperative bariatric surgery patients.

CONCLUSION

Pharmacists have an increasing role in the chronic management of the bariatric surgery patient due to their knowledge of medication dosage forms and expertise in disease states affected by bariatric surgery.

Review article: The nutritional and pharmacological consequences of obesity surgery

BACKGROUND

Obesity surgery is acknowledged as a highly effective therapy for morbidly obese patients. Beneficial short-term effects on common comorbidities are practically undisputed, but a growing data pool from long-term follow-up reveals increasing evidence of potentially severe nutritional and pharmacological consequences.

AIMS

To assess the prevalence, causes and symptoms of complications after obesity surgery, to elucidate and compare therapy recommendations for macro- and micronutrient deficiencies, and to explore surgically-induced effects on drug absorption and bioavailability, discussing ramifications for long-term therapy and prophylaxis.

METHODS

PubMed, Embase and MEDLINE were searched using terms including, but not limited to, bariatric surgery, gastric bypass, obesity surgery and Roux-en-Y, coupled with secondary search terms, e.g. anaemia, micronutrients, vitamin deficiency, bacterial overgrowth, drug absorption, pharmacokinetics, undernutrition. All studies in English, French or German published January 1980 through March 2014 were included.

RESULTS

Macro- and micronutrient deficiencies are common after obesity surgery. The most critical, depending on surgical technique, are hypoalbuminemia (3-18%) and deficiencies of vitamins B1 (≤49%), B12 (19-35%) and D (25-73%), iron (17-45%) and zinc (12-91%). Many drugs commonly administered to obese patients (e.g. anti-depressants, anti-microbials, metformin) are subject to post-operative and/or PPI-associated changes affecting bioavailability and absorption.

CONCLUSIONS

Complications are associated with pre-operative and/or post-operative malnutrition or procedure-related changes in intake, absorption and drug bioavailability. The high prevalence of nutrient deficiencies after obesity surgery makes life-long nutritional monitoring and supplementation essential. Post-operative changes to drug absorption and bioavailability in bariatric patients cast doubt on the validity of standard drug dosage and administration recommendations.

Moxifloxacin dosing in post-bariatric surgery patients

INTRODUCTION

Given the ever increasing number of obese patients and obesity related bypass surgery, dosing recommendations in the post-bypass population are needed. Using a population pharmacokinetic (PK) analysis and PK-pharmacodynamic (PD) simulations, we investigated whether adequate moxifloxacin concentrations are achieved in this population.

METHODS

In this modelling and simulation study we used data from a trial on moxifloxacin PK. In this trial, volunteers who had previously undergone bariatric surgery (at least 6 months prior to inclusion), received two doses (intravenous and oral) of 400 mg moxifloxacin administered on two occasions.

RESULTS

In contrast to other papers, we found that moxifloxacin PK were best described by a three compartmental model using lean body mass (LBM) as a predictor for moxifloxacin clearance. Furthermore, we showed that the probability of target attainment for bacterial eradication against a hypothetical Streptococcus pneumoniae infection is compromised in patients with higher LBM, especially when targeting microorganisms with minimum inhibitory concentrations (MICs) of 0.5 mg l(-1) or higher (probability of target attainment (PTA) approaching zero). When considering the targets for suppression of bacterial resistance formation, even at MIC values as low as 0.25 mg l(-1) , standard moxifloxacin dosing does not attain adequate levels in this population. Furthermore, for patients with a LBM of 78 kg or higher, the probability of hitting this target approaches zero.

CONCLUSIONS

Throughout our PK-PD simulation study, it became apparent that, whenever optimal bacterial resistance suppression is deemed necessary, the standard moxifloxacin dosing will not be sufficient. Furthermore, our study emphasizes the need for a LBM based individualized dosing of moxifloxacin in this patient population.

Evaluation of an In Silico PBPK Post-Bariatric Surgery Model through Simulating Oral Drug Bioavailability of Atorvastatin and Cyclosporine

An increasing prevalence of morbid obesity has led to dramatic increases in the number of bariatric surgeries performed. Altered gastrointestinal physiology following surgery can be associated with modified oral drug bioavailability (Foral). In the absence of clinical data, an indication of changes to Foral via systems pharmacology models would be of value in adjusting dose levels after surgery. A previously developed virtual "post-bariatric surgery" population was evaluated through mimicking clinical investigations on cyclosporine and atorvastatin after bariatric surgery. Cyclosporine simulations displayed a reduced fraction absorbed through gut wall (fa) and Foral after surgery, consistent with reported observations. Simulated atorvastatin Foral postsurgery was broadly reflective of observed data with indications of counteracting interplay between reduced fa and an increased fraction escaping gut wall metabolism (FG). Inability to fully recover observed atorvastatin exposure after biliopancreatic diversion with duodenal switch highlights the current gap regarding the knowledge of associated biological changes.CPT: Pharmacometrics & Systems Pharmacology (2013) 2, e47; doi:10.1038/psp.2013.23; advance online publication 12 June 2013.

A mechanistic pharmacokinetic model to assess modified oral drug bioavailability post bariatric surgery in morbidly obese patients: interplay between CYP3A gut wall metabolism, permeability and dissolution

Objectives

Due to the multi-factorial physiological implications of bariatric surgery, attempts to explain trends in oral bioavailability following bariatric surgery using singular attributes of drugs or simplified categorisations such as the biopharmaceutics classification system have been unsuccessful. So we have attempted to use mechanistic models to assess changes to bioavailability of model drugs.

Methods

Pharmacokinetic post bariatric surgery models were created for Roux-en-Y gastric bypass, biliopancreatic diversion with duodenal switch, sleeve gastrectomy and jejunoileal bypass, through altering the ‘Advanced Dissolution Absorption and Metabolism’ (ADAM) model incorporated into the Simcyp® Simulator. Post to pre surgical simulations were carried out for five drugs with varying characteristics regarding their gut wall metabolism, dissolution and permeability (simvastatin, omeprazole, diclofenac, fluconazole and ciprofloxacin).

Key findings

The trends in oral bioavailability pre to post surgery were found to be dependent on a combination of drug parameters, including solubility, permeability and gastrointestinal metabolism as well as the surgical procedure carried out.

Conclusions

In the absence of clinical studies, the ability to project the direction and the magnitude of changes in bioavailability of drug therapy, using evidence-based mechanistic pharmacokinetic in silico models would be of significant value in guiding prescribers to make the necessary adjustments to dosage regimens for an increasing population of patients who are undergoing bariatric surgery.

Drug interactions: a primer for the gastroenterologist

One of the most clinically significant complications related to the use of pharmacotherapy is the potential for drug-drug or drug-disease interactions. The gastrointestinal system plays a large role in the pharmacokinetic profile of most medications, and many medications utilized in gastroenterology have clinically significant drug interactions. This review will discuss the impact of alterations of intestinal pH, interactions mediated by phase I hepatic metabolism enzymes and P-glycoprotein, the impact of liver disease on drug metabolism, and interactions seen with commonly utilized gastrointestinal medications.