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Prescribing challenges following bariatric surgery


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Obesity is an increasing problem in the UK, with over half of the population being overweight or obese. The use of gastric surgery is increasing, with a 5% increase in 2016/17 compared to 2015/16. However, little is known about ideal drug formulations after bariatric surgery. An exploratory literature search of research databases was carried out to address this. The authors found that there was a dearth of high-quality primary studies available, with many studies using low numbers of participants. The major finding was of the need for increased vigilance and monitoring of patients after surgery.
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The statistics surrounding obesity in the UK
are concerning. The prevalence of people
who are overweight or obese was 57% for
women and 66% for men in 2016 (NHS
Digital, 2017). The prevalence of obesity alone
has increased from 15% of the population in 1993
to 27% by 2015 (NHS Digital, 2017). This is an
increasing trend worldwide, with the UK currently
having the dubious value of being near the top
of the league table for obesity prevalence; ranked
sixth out of 34 countries (NHS Digital, 2018).
The same statistics reveal that 617 000 admissions
to hospital in 2016/17 were related to obesity, an
increase of 18% on the previous year. There was a
5% increase in admissions for bariatric surgery in
2016/17 compared to 2015/16 from 6000 to 6760,
although the total number has not reached the
peak seen in 2011/12 (NHS Digital, 2018).
The four most common surgical interventions
for the management of obesity are Roux-en-Y
gastric bypass, sleeve gastrectomy, laparoscopic
gastric band and biliopancreatic diversion with
duodenal switch. The Roux-en-Y gastric bypass
is the most common intervention, and has
been reviewed for safety and efcacy of surgical
procedures (Guller et al, 2009). A meta-analysis
showed that the Roux-en–Y bypass was superior
to alternative surgical options in obtaining weight
loss (Zhang et al, 2014). While there has been
some controversy surrounding which approach
is best, the likely superiority of the Roux-en-Y
approach was upheld by Ettleson et al (2017).
The Roux-en Y bypass involves reducing the
volume of the stomach by approximately 98%. The
normal volume of the stomach is 1,500 ml, but
this is reduced to approximately 30 ml after the
procedure. In addition, a shortened length of the
small intestine is attached to the smaller pouch of
the stomach, thus reducing absorption through the
small intestine and affecting the body’s ability to
absorb minerals and drugs.
Managing long-term conditions after major
surgery is potentially complex. Therefore, it is
opportune to review the available literature on
absorption of drugs post bariatric surgery.
Little is known about the impact of bariatric
surgery on patients’ medication burden or the
absorption of drugs (Azran et al, 2017).
We therefore decided to undertake an
exploratory literature search of the available
evidence to inform best practice for addressing
prescribing challenges after bariatric surgery. We
conducted a literature review with assistance
from the university librarian. We noted the
relative dearth of primary sourced evidence on
drug absorption and concluded that enhanced
monitoring in regards to drug management is a key
need post surgery.
Prescribing challenges after
bariatric surgery
Colin Waldock and David Bedford
Obesity is an increasing problem in the UK, with over half the population being
overweight or obese. The use of gastric surgery is increasing, with a 5% increase
in 2016/17 compared to 2015/16. However, little is known about ideal drug
formulations after bariatric surgery. An exploratory literature search of research
databases was carried out to address this. We found that there was a dearth
of high-quality primary studies available, with many studies using low numbers
of participants. The major finding was of the need for increased vigilance and
monitoring of patients after surgery.
Key words: bariatric surgery | obesity | safe practice | drug formulation
Colin Waldock
Lecturer, Medway School of Pharmacy,
Universities of Kent and Greenwich
David Bedford
Librarian, University of Greenwich
344 Journal of Prescribing Practice 2019 Vol 1 No 9
© 2019 MA Healthcare Ltd
Assistance was sought from the university library to
conduct an exploratory literature search for relevant
articles in English using the following terms: bariatric
surgery, weight loss surgery, prescribing, prescriber,
prescribers, prescribe, dosage form, dosage forms,
pharmacotherapy, pharmacotherapeutic, formulation,
absorb, absorption and absorbance.
The search databases Cinahl and Medline
were used, yielding a high number of results
unconnected with the question. The search was
further rened by adding the following terms to
focus the results on postoperative management:
after, following, postoperative, post-operative,
postsurgical, post-surgical.
The records retrieved were screened to ensure
inclusion only of English language research articles
relevant to the question (eg, to remove articles
relating to absorption of food or comparisons of
weight-loss surgery to pharmacotherapy).
The principal author then searched for duplicates
and conducted a review of the titles and abstracts
for relevance to the study, utilising the Critical
Appraisal Skills Programme (CASP) tool to aid in
decision-making as to relevance. This process led
to the exclusion of a further 41 articles, leaving 53
to be reviewed (Figure 1). Five of these studies were
excluded after reading (Table 1).
The 48 articles in the review covered a variety of
topics and used several types of study methods
(Table 2). It is clear from these numbers that there
is a dearth of literature using controlled trials to
investigate absorption and issues affecting drug
formulation after bariatric surgery.
It is notable that low numbers of subjects have
been involved in these trials, which might be
considered to be a signicant limitation.
Mischler et al (2018) studied 14 subjects to
investigate what type of iron formulation to
recommend after bariatric surgery. In the largest
study, Ring Madsen et al (2018) studied 39 subjects
to assess the effectiveness of calcium citrate
versus calcium carbonate on elevated parathyroid
hormone after Roux-en-Y gastric bypass. The
lowest number of subjects was eight (Rocha
et al, 2019). There is a requirement for large,
high-quality randomised controlled trials to be
developed in order to inform practice.
There are also some case reports in the literature.
Three of these studied liquid levothyroxine as an
alternative to the tablet formulation after bariatric
surgery (Fallahi at al, 2017; Hommel and Delgrange,
2017; Pirola et al, 2013). While the use of liquid
formulations appears to be supported by these
reports, it is worth considering the cost of liquid and
soft gel formulations. Levothyroxine 100 microgram
tablets cost 4p per day, whereas the equivalent liquid
formulation is £5.72 per day (100 microgram/5 ml)
(Joint Formulary Committee, 2018).
Azran et al (2017) presented a case of a patient
who had a lower absorption of oral methylphenidate
after bariatric surgery. They discussed a second case
(Ludvigsson and Haenni, 2016) where the patient
suffered methylphenidate toxicity after surgery. The
contradictory effects in these two cases suggest that
methylphenidate absorption is unpredictable post
surgery. Further work is clearly needed and patients
should be closely monitored in order to avoid under-
or overdose of methylphenidate.
Darwich et al (2012) used simulation models to
assess the likely pharmacokinetic effects on a range
of drugs after bariatric surgery. They found that
adverse effects on absorption were dependent on a
range of factors and made recommendations to use
Table 1. Excluded articles
Author Study type Reason for exclusion
Yska et al (2016b) Randomised
controlled trial
Not applicable because it was
a randomised controlled trial of
behaviour of clinicians and not
drug absorption
Yska et al (2016a) Systematic review Excluded as not relevant to the
Macgregor and Boggs
Literature review Excluded as article superseded by
recent developments
Muzard et al (2017) Case series Excluded as area of study too
specic, focused on gastric sleeve
and only had four subjects.
Gomez-Ramirez et al
Non research Excluded because this was a
non research article on drug
formulations and not related to use
in bariatric surgery
Table 2. Types of articles reviewed
The 48 articles included in the review covered a variety of topics and used
several methods
Type Number of articles
Review 28
Cohort study 2
Controlled trial 6
Crossover trial 1
Case reports 4
Single dose pharmacokinetic study 4
Qualitative 2
Simulation model based 1
Journal of Prescribing Practice 2019 Vol 1 No 9 345
© 2019 MA Healthcare Ltd
best evidence from these models to predict required
dosage adjustments.
In our review, no further published material was
found that used simulation models.
In vitro models showed that 10 out of 22
psychotropic medicines have altered absorption,
while cyclosporin, phenytoin and thyroxine also have
changes in absorption (Seaman et al, 2005).
The majority of articles in this literature review
were themselves reviews, with the majority arguing
for close monitoring of patients after surgery. Padwal
et al (2010) stated that the effects post surgery appear
to be drug specic, with the most consistent evidence
for reduced absorption found for cyclosporine,
levothyroxine, phenytoin and rifampicin.
Sawaya et al (2012) reviewed vitamin and
mineral deciency, with emphasis on the likelihood
of patients developing vitamin B12 deciency
after bariatric surgery. This led to guidance
recommending routine vitamin B12 intramuscular
injections for three months post-operatively
(O’Kane et al, 2014).
Stein et al (2014) concluded that life-long
monitoring of patients was essential, echoed in
a review of levothyroxine dosage by Azran et al
(2019). Yska et al (2013) noted the dearth of high-
quality studies on dosage and formulations, while
Schlatter (2017) highlighted the need for more
research into oral contraception after bariatric
In a review of anticoagulation, Martin et al
(2017) argued for the increased role of pharmacists
in post-surgical management. Greenblatt and
Greenblatt (2015) supported this, and noted that
any alteration in drug behaviour could be due to
a range of factors, including the surgery itself and
subsequent weight change.
Titus et al (2013) mentioned the lack of large
trials, but noted the relatively larger number of
small case studies and individual reports, again
calling for more work of high calibre, which was
echoed by other authors (Mitchell at al, 2013;
Azran at al, 2016).
A small number of single-dose pharmacokinetic
studies have shown that venlafaxine extended
release is unaffected by bariatric surgery (Krieger et
al, 2017). However, azithromycin is affected, with
a reduction of up to 30% in peak concentration in
patients undergoing bariatric surgery compared with
age-matched controls (Padwal et al, 2012).
Chan et al (2015) conducted a single-dose
pharmacokinetic study on midazolam and digoxin,
Figure 1. Selection process
Identication Records identied after database searching
Records after duplicates removed
Screening Records screened
Records excluded
Eligibility Full text articles assessed for eligibility
Full text excluded with reasons
Included Studies included
346 Journal of Prescribing Practice 2019 Vol 1 No 9
© 2019 MA Healthcare Ltd
and showed an increase in drug absorption rate
but no effect on overall exposure of the drug to the
individual. In a similar study design, Gesquiere et
al (2016) looked at fenobrate and posaconazole.
They found a marked reduction in the absorption
of posaconazole, highlighting the potential for early
treatment failure and the need for close monitoring.
The number of bariatric surgery procedures is
increasing. This surgery has the potential to reduce
prescribing for a wide range of drugs, including
insulins, oral diabetes medications, beta-blockers,
statins, NSAIDs and antidepressants, and reduce the
indicdence of hypertension and type 2 diabetes (Yska
et al, 2013; Bland et al, 2016).
There is a lack of high-quality, long-term large
studies. The current literature recommends close
monitoring of the patient for an extended time after
bariatric surgery.
Drug-specic changes have been reported in
single-dose pharmacokinetic studies (Padwal et al,
2012; Chan et al 2015; Gesquiere et al, 2016; Krieger
et al, 2017). There is potential for the use of drug
simulation models (Darwich et al, 2012). Liquid
formulations of levothyroxine have been promoted,
but the effect on costs needs to be considered.
Individual attention to patient needs and a patient-
centred model of care is recommended to best meet
the needs of this complex cohort. Pharmacists could
have an increased role to play in the post-operative
management phase. JPrP
Acknowledgements: Denise Rabbette and Teresa
Benniman, Medway School of Pharmacy Universities of
Kent and Greenwich, for peer review prior to submission
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Full-text available
Background Bariatric surgery leads to several anatomo-physiological modifications that may affect pharmacokinetic parameters and consequently alter the therapeutic effect of drugs, such as antibiotics. The pharmacokinetics of oral amoxicillin after Roux-en-Y gastric bypass (RYGB) surgery is unknown. Objectives The objective of this study was to evaluate the impact of bariatric surgery on the pharmacokinetics of amoxicillin. Methods This study was performed as a randomized, open-label, single-dose clinical trial, with two periods of treatment, in which obese subjects (n = 8) received an amoxicillin 500 mg capsule orally before and 2 months after the RYGB surgery. The amoxicillin plasma concentration was determined by liquid chromatography coupled to mass spectrometry (LC-MS/MS). Results After the surgery, the mean weight loss was 17.03 ± 5.51 kg, and mean body mass index (BMI) decreased from 46.21 ± 2.82 to 38.82 ± 3.32 kg/m². The mean amoxicillin area under the plasma concentration versus time curve from time zero to the time of the last quantifiable concentration (AUC0–tlast) increased significantly (3.5-fold); the maximum plasma concentration (Cmax) increased 2.8-fold after the bariatric surgery. No correlation was found between amoxicillin absorption, BMI, and weight loss percentage. Conclusion The alterations observed in the amoxicillin pharmacokinetics suggest that obese subjects included in this trial had a substantially increase in amoxicillin systemic exposure after RYGB surgery. However, despite this increase, its exposure was lower than the values reported for non-obese volunteers. Trial Registration Identifiers: NCT03588273
Full-text available
Iron deficiency (ID) is usually treated with oral iron salts, but up to 50% of patients complain of gastrointestinal side effects, leading to reduced treatment compliance. Intravenous (IV) iron formulations are increasingly safer, but there is still a risk of infusion and hypersensitivity reactions and the need for a venous access and infusion monitoring. Sucrosomial® iron (SI) is an innovative oral iron formulation in which ferric pyrophosphate is protected by a phospholipid bilayer plus a sucrester matrix (sucrosome), which is absorbed through para-cellular and trans-cellular routes (M cells). This confers SI unique structural, physicochemical and pharmacokinetic characteristics, together with high iron bioavailability and excellent gastrointestinal tolerance. The analysis of available evidence supports oral SI iron as a valid option for ID treatment, which is more efficacious and better tolerated than oral iron salts. SI has also demonstrated similar effectiveness, with lower risks, in patients usually receiving IV iron (e.g., chronic kidney disease, cancer, bariatric surgery). Thus, oral SI emerges as a most valuable first option for treating ID, even more for subjects with intolerance to or inefficacy of iron salts. Moreover, SI should be also considered as an alternative to IV iron for initial and/or maintenance treatment in different patient populations.
Full-text available
Objective Following Roux‐en‐Y gastric bypass (RYGB), elevated parathyroid hormone (PTH) levels potentially harmful to bone health are commonly observed. Owing to assumed superior absorption, calcium citrate is often recommended over calcium carbonate following RYGB for the treatment of elevated PTH. We aimed to investigate the impact of either calcium carbonate or calcium citrate (1200 mg elementary calcium) in patients with elevated PTH levels following RYGB. Design Clinical, double‐blinded, randomized controlled trial of a 12‐week‐duration at a Danish University Hospital. Patients and measurements Thirty‐nine (no drop out) RYGB operated patients with elevated PTH levels (PTH>6.9 pmol/l) and normal plasma levels of calcium and 25‐hydroxyvitamin D were randomized to either calcium carbonate or calcium citrate (1200 mg elementary calcium/daily). We assessed change in PTH as the primary outcome. Results The effect of the two calcium formulations on change in PTH was comparable and neutral: ‐1.9% (calcium citrate) vs +0.9% (calcium carbonate), p=0.680. Compared to the carbonate‐treated group, the following bone turnover markers decreased significantly in the citrate‐treated group: procollagen I N‐terminal propeptide (‐16.6% vs ‐3.2%, p=0.021), osteocalcin (‐17.2% vs ‐4.3%, p= 0.007), and bone‐specific alkaline phosphatase (‐5.9% vs 3.7%, p=0.027) and remained significantly decreased after multivariable adjustment. Conclusion Increasing the dose of calcium supplementation in RYGB operated patients with slightly elevated PTH levels does not normalize PTH levels, regardless of the type of supplement. Our results do not support recommending supplementation with calcium citrate over calcium carbonate in RYGB patients. This article is protected by copyright. All rights reserved.
Full-text available
Background: The evidence behind recommendations for treatment of iron deficiency (ID) following roux-en-y gastric bypass surgery (RYGB) lacks high quality studies. Setting: Academic, United States OBJECTIVE: The objective of the study is to compare the effectiveness of oral iron supplementation using non-heme versus heme iron for treatment of iron deficiency in RYGB patients. Methods: In a randomized, single-blind study, women post-RYGB and iron deficient received non-heme iron (FeSO4, 195 mg/day) or heme iron (heme-iron-polypeptide, HIP, 31.5 to 94.5 mg/day) for 8 weeks. Measures of iron status, including blood concentrations of ferritin, soluble transferrin receptor (sTfR), and hemoglobin, were assessed. Results: At baseline, the mean ± standard deviation for age, BMI, and years since surgery of the sample was 41.5 ± 6.8 years, 34.4 ± 5.9 kg/m(2), and 6.9 ± 3.1 years, respectively; and there were no differences between FeSO4 (N = 6) or HIP (N = 8) groups. Compliance was greater than 94%. The study was stopped early due to statistical and clinical differences between groups. Values before and after FeSO4 supplementation, expressed as least square means (95% CI) were hemoglobin, 10.8 (9.8, 11.9) to 13.0 (11.9, 14.0) g/dL; sTfR, 2111 (1556, 2864) to 1270 (934, 1737) μg/L; ferritin, 4.9 (3.4, 7.2) to 15.5 (10.6, 22.6) μg/L; and sTfR:ferritin ratio, 542 (273, 1086) to 103 (51, 204); all p < 0.0001. With HIP supplementation, no change was observed in any of the iron status biomarkers (all p > 0.05). Conclusions: In accordance with recommendations, oral supplementation using FeSO4, but not HIP, was efficacious for treatment of iron deficiency after RYGB.
Full-text available
Objective: Bariatric surgery offers a highly effective mode of treatment for obese patients. Some procedures such as bypass cause an alteration in normal gastrointestinal tract with possible consequences for the uptake of orally administered drugs. Methods: We assessed the literature to ascertain whether the use of oral drugs and especially oral contraceptives is effective and adequate after bariatric surgery. Results: The bioavailability of drugs could be affected by the solubility and pH of the modified medium after bariatric surgery and by the loss of gastrointestinal transporters. Bariatric surgery could potentially result in a transient change in the absorption of drugs such as analgesics, antibiotics, antiarrhythmics, anticoagulants, psychotropic, and oral contraceptive drugs. Effective contraception is especially critical in the postoperative period, and implants might be representing a safe contraceptive method in women undergoing bariatric surgery. Conclusion: Each drug will have to be evaluated with respect to its site of absorption and its mechanism of absorption, with special attention on parameters influencing the effectiveness of the absorption processes.
Background: Bariatric surgery can lead to changes in the oral absorption of many drugs. Levothyroxine is a narrow therapeutic drug for hypothyroidism, a common condition among patients with obesity. Objective: The purpose of this work was to provide a mechanistic overview of levothyroxine absorption, and to thoroughly analyze the expected effects of bariatric surgery on oral levothyroxine therapy. Methods: We performed a systematic review of the relevant literature reporting the effects of bariatric surgery on oral levothyroxine absorption and postoperative thyroid function. A PubMed search for relevant keywords resulted in a total of 14 articles reporting levothyroxine status before versus after bariatric surgery. Results: Different mechanisms may support opposing trends as to levothyroxine dose adjustment postsurgery. On the one hand, based on impaired drug solubility/dissolution attributable to higher gastric pH as well as reduced gastric volume, compromised levothyroxine absorption is expected. On the other hand, the great weight loss, and altered set-point of thyroid hormone homeostasis with decreased thyroid-stimulating hormone after the surgery, may result in a decreased dose requirement. Conclusions: For patients after bariatric surgery, close monitoring of both the clinical presentation and plasma thyroid-stimulating hormone and T4 levels is strongly advised. Better understanding and awareness of the science presented in this article may help to avoid preventable complications and provide optimal patient care.
Study objective: The extended-release (ER) form of venlafaxine is preferred because of improved patient adherence, but the immediate-release form is frequently used after Roux-en-Y gastric bypass surgery (RYGB) because of concerns for malabsorption. The objective of this study was to determine whether a statistically significant and predictable change in the bioavailability of venlafaxine ER capsules occurs after RYGB. Design: Prospective, nonblinded, single-dose pharmacokinetic study. Setting: Clinical research unit at a large, tertiary care medical practice. Patients: Ten adult pre-bariatric surgery patients who met the criteria for noncomplicated RYGB were enrolled and served as their own controls. Interventions: Patients were administered one venlafaxine ER 75-mg capsule at two visits-the first visit at least 1 week before undergoing RYGB and the second visit 3-4 months after RYGB. Blood samples were collected at predetermined intervals over 48 hours after each dose, and the pharmacokinetics of venlafaxine were measured. Measurements and main results: Plasma levels of venlafaxine and its primary metabolite, O-desmethylvenlafaxine (ODV), were compared at baseline and 3-4 months after RYGB. The areas under the serum concentration-time curves from 0-24 hours (AUC0-24 ) for venlafaxine (mean ± SD 734 ± 602 vs 630 ± 553 ng•hr/mL, P=0.22) and ODV (mean ± SD 894 ± 899 vs 1083 ± 972 ng•hr/mL, P =0.07) were similar before and after RYGB. Using a bioequivalence approach, differences in pre-RYGB and post-RYGB values of AUC0-24 , peak serum concentration, and time to peak serum concentration were not statistically significant for either venlafaxine or ODV. Conclusion: This study suggests that RYGB does not significantly alter the amount of venlafaxine or its active metabolite, ODV, absorbed from a venlafaxine ER capsule or the time over which it is absorbed. This article is protected by copyright. All rights reserved.
The anatomical and physiological changes in the gastrointestinal (GI) tract following bariatric surgery may significantly affect the pharmacokinetics of medications taken by the patients, from various reasons. Unfortunately, there is little information regarding changes in drug absorption after bariatric surgeries, limiting the ability of medical professionals to produce clear recommendations on what changes should be made to the formulations and dosing regimens of drugs following bariatric surgery.
Bariatric surgery may alter the absorption, distribution, metabolism and/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 presently available data, it appears most prudent to use warfarin with INR monitoring, and not direct oral anticoagulants, when full-dose anticoagulation is needed after bariatric surgery.
Aims: Roux-en-Y gastric bypass (RYGB) alters the anatomical structure of the GI-tract, which can result in alterations in drug disposition. The aim of this 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 of fenofibrate (Lipanthyl®) and 400 mg of posaconazole (Noxafil®) was performed in 12 volunteers pre- and post-RYGB, In the posaconazole study one patient dropped out. After oral administration, blood samples were collected at different time-points up to 48 h after administration. Plasma concentrations were determined by HPLC in order to calculate AUC0-48h , Cmax and Tmax . Results: After administration of fenofibrate, no relevant differences in AUC0-48h , Cmax and Tmax between pre- and post-operative setting were observed. The geometric mean of the ratio of AUC0-48h pre/post-RYGB for fenofibrate was 0.91 (95% CI 0.72; 1.15)(P = 0.40). For posaconazole, an important decrease in AUC0-48h and Cmax following RYGB was shown; the geometric mean of the AUC0-48h pre/post-RYGB ratio was 1.48 (95% CI 1.04; 2.10) (P = 0.03) and the geometric mean of the Cmax pre/post-RYGB ratio was 1.66 (95% CI 1.07; 2.58)(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 Tmax was observed. Conclusions: The disposition of fenofibrate was not altered after RYGB, whereas the oral disposition of posaconazole was significantly decreased following RYGB.