Disposition of temozolomide in a patient with glioblastoma multiforme after gastric bypass surgery

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Drug absorption in bariatric surgery patients: A narrative review

Background

Despite the increase in the number of bariatric surgeries performed, little is known about the impact of the surgery on drug absorption. Unpredictability is assumed with drugs, given the anatomical changes after surgery.

Objective

To evaluate the impact of bariatric surgery on drug absorption based on the type of procedure performed.

Methods

We conducted a comprehensive literature review searching PubMed/Medline for published studies (from inception to December 2017) that evaluate the use of drugs and the assessment of drug absorption after bariatric surgery. Pharmacokinetic/pharmacodynamic studies, case reports, and observational studies were included in our review.

Results

We found 60 studies addressing drug use after bariatric surgery. Twenty‐eight studies reported a decrease in drug absorption after bariatric surgery while only four studies showed an increase in drug absorption. Unchanged absorption of drugs was seen in 23 studies after the surgery.

Conclusion

The available information shows variations in drug absorption after bariatric surgery. The unpredictability may result from factors related to the patient, drug, and/or type of surgery. Therefore, pharmacists' involvement and close monitoring of patients after bariatric surgery could be effective to avoid sub‐/supratherapeutic responses.

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.

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.

Clinicians' prescribing practices for bariatric surgery patients: is there an issue?

WHAT IS KNOWN AND OBJECTIVES

Patients undergoing Roux-en-Y gastric bariatric (RYGB) surgery present a reduced absorption site, and special attention should therefore be taken when prescribing oral-dosage forms. This study was carried out to investigate the extent to which non-bariatric clinicians are aware of this issue when prescribing medicines for this population, and what type of information is available to aid them in their decision-making.

METHODS

Two questionnaires were created, one for non-bariatric clinicians and another for their patients who had undergone RYGB surgery, to gather information about the prescription practices for this population. Additionally, a literature search of pharmacokinetic studies on bariatric patients and recommended prescription practices was carried out.

RESULTS AND DISCUSSION

Of the 62 non-bariatric clinicians surveyed, 50% believed RYGB surgery interferes with drug absorption; however, 68% still prescribed tablets as the first choice form of dosage. Young clinicians (35%) were less likely to believe that RYGB surgery could affect drug absorption than experienced clinicians (43%). The main reasons for changing dosage forms were patient complaints about efficacy or difficulty in swallowing tablets. Of the 73 patients, 43 were taking drugs in tablet form after the surgery, 24 of whom had health issues unrelated to the surgery. None of the journals read by the clinicians contained pharmacokinetics (PK) studies involving bariatric surgery patients or presented recommendations for the prescription of oral-dosage forms for this population. The literature search revealed a total of 22 drugs that had undergone PK studies in RYGB patients. Fifteen of them were reported to have decreased effects, 12 of which were administered as tablets.

WHAT IS NEW AND CONCLUSION

There is still a relative lack of clinical evidence to guide clinicians when prescribing medicines for bariatric patients. It is therefore recommended that pharmacists should have greater participation in the prescription process to advise non-bariatric clinicians and educate RYGB surgery patients to help avoid therapeutic failure.

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

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

Changes to oral drug bioavailability have been observed post bariatric surgery. However, the magnitude and the direction of changes have not been assessed systematically to provide insights into the parameters governing the observed trends. Understanding these can help with dose adjustments.

WHAT THIS STUDY ADDS

Analysis of drug characteristics based on a biopharmaceutical classification system is not adequate to explain observed trends in altered oral drug bioavailability following bariatric surgery, although the findings suggest solubility to play an important role.

AIMS

To identify the most commonly prescribed drugs in a bariatric surgery population and to assess existing evidence regarding trends in oral drug bioavailability post bariatric surgery.

METHODS

A retrospective audit was undertaken to document commonly prescribed drugs amongst patients undergoing bariatric surgery in an NHS hospital in the UK and to assess practice for drug administration following bariatric surgery. The available literature was examined for trends relating to drug permeability and solubility with regards to the Biopharmaceutics Classification System (BCS) and main route of elimination.

RESULTS

No significant difference in the 'post/pre surgery oral drug exposure ratio' (ppR) was apparent between BCS class I to IV drugs, with regards to dose number (Do) or main route of elimination. Drugs classified as 'solubility limited' displayed an overall reduction as compared with 'freely soluble' compounds, as well as an unaltered and increased ppR.

CONCLUSION

Clinical studies establishing guidelines for commonly prescribed drugs, and the monitoring of drugs exhibiting a narrow therapeutic window or without a readily assessed clinical endpoint, are warranted. Using mechanistically based pharmacokinetic modelling for simulating the multivariate nature of changes in drug exposure may serve as a useful tool in the further understanding of postoperative trends in oral drug exposure and in developing practical clinical guidance.

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

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

Advances in the management of glioblastoma: the role of temozolomide and MGMT testing

Glioblastoma (GB) is one of the most lethal forms of cancer, with an invasive growth pattern that requires the use of adjuvant therapies, including chemotherapy and radiation, to prolong survival. Temozolomide (TMZ) is an oral chemotherapy with a limited side effect profile that has become the standard of care in GB treatment. While TMZ has made an impact on survival, tumor recurrence and TMZ resistance remain major challenges. Molecular markers, such as O6-methylguanine-DNA methyltransferase methylation status, can be helpful in predicting tumor response to TMZ, and therefore guides clinical decision making. This review will discuss the epidemiology and possible genetic underpinnings of GB, how TMZ became the standard of care for GB patients, the pharmacology of TMZ, the practical aspects of using TMZ in clinic, and how molecular diagnostics – particularly the use of O6-methylguanine-DNA methyltransferase status – affect clinical management.

Oral bioavailability of linezolid before and after Roux-en-Y gastric bypass surgery: is dose modification necessary in obese subjects?

OBJECTIVES

We characterized the pharmacokinetics of intravenous (iv) and oral linezolid before and after Roux-en-Y gastric bypass surgery (RYGBS).

METHODS

Subjects with a body mass index (BMI)  >35 kg/m(2) received a single iv 600 mg dose of linezolid followed by the same oral dose after a 7 day washout period between doses, before and 3 months after RYGBS. Serum linezolid concentrations were measured by a validated HPLC method with ultraviolet detection. Parametric population pharmacokinetic analysis was used to evaluate bioavailability and the influence of total body weight (TBW) on pharmacokinetic parameters. The area under the serum concentration-time curve extrapolated to infinity (AUC(0-∞)) was compared between subjects before and after RYGBS, and with non-obese controls.

RESULTS

Five (four male) obese subjects were studied with a mean (SD) age of 51.4 (5.01) years, TBW of 124 (10.6) kg and initial BMI of 44.9 (7.52) kg/m(2). The bioavailability was a mean (95% CI) of 1.14 (0.816-1.47) before and 1.14 (1.01-1.26) after RYGBS. The mean (SD) AUC(0-∞) with oral linezolid before RYGBS was 41.6 (20.9) mg h/L compared with 98.9 (24.7) mg h/L after RYGBS (P<0.001). This increase in AUC(0-∞) corresponded with a 25.3% reduction in the TBW after RYGBS, as the TBW was a significant covariate of clearance. The probability of pharmacodynamic target attainment with standard doses of linezolid is lower in obese versus non-obese individuals.

CONCLUSIONS

The bioavailability of linezolid is not impaired by RYGBS. The serum exposure of linezolid is more than 50% lower in obese compared with non-obese subjects, suggesting that dose modification may be needed.