Advising on specific medicines following bariatric surgery

Using our advice

Before considering specific medicines, ensure you are familiar with our general guidance for using medicines following bariatric surgery. Considerations include the type of surgery, altered pharmacokinetics of medicines, and patient choice.

• Considerations for using medicines following bariatric surgery

Considerations

This page covers medicines which are commonly used, or are considered high risk, and where there is useful information to consider. Exclusion of a medicine does not necessarily mean that bariatric surgery does not have any impact.

There is often no data on safety or experience of use following bariatric surgery. Use should therefore be based on an individual risk versus benefit decision.

Not all types of bariatric surgery will affect the medicines in the ways described below. It is therefore important to consider the exact type of bariatric surgery and how this might affect drug handling, in any given scenario.

Monitoring

When medicines are used following bariatric surgery, the patient should be monitored for changes in clinical efficacy and adverse effects. Dose adjustments, changes to the route of administration, or changing the medicine should be considered where necessary.

As food intake and weight changes in the weeks and months after the surgery, this needs to be taken into account when considering the frequency of monitoring, the dosing, and making any adjustments.

Medicines with a narrow therapeutic window, will require more careful management.

Vitamins and Supplements

Guidance is available from the British Obesity and Metabolic Surgery Society (BOMSS) on recommended vitamins and supplements following bariatric surgery.

Guidance is also available from NICE regarding vitamin B12 supplementation

Cardiovascular

Many cardiovascular medicines can be affected by bariatric surgery and patients should be monitored.

Antihypertensives

Bariatric surgery may affect the absorption of antihypertensives. Monitor blood pressure for clinical efficacy, and consider dose alterations or alternative antihypertensives if necessary.

Substantial weight loss following bariatric surgery can also lower blood pressure, potentially reducing the need for antihypertensives. Monitor the patient, and consider reducing the dose, or stopping the antihypertensive if clinically appropriate.

Statins

Bariatric surgery may affect the absorption of statins.

Patients should be monitored closely for both therapeutic effects, for example serum lipids, and adverse effects in the first years after the surgery.

Amiodarone

Amiodarone is a highly lipophilic drug that accumulates in adipose tissue. Rapid weight loss may result in the release of large amounts of amiodarone into the circulation with resultant thyrotoxicosis or other adverse effects.

Bioavailability may also be reduced by shortened gastrointestinal transit time.

Monitor for clinical efficacy and adverse effects, and consider dose alterations as required.

Direct Oral Anticoagulation (DOACs) and Warfarin

Direct Oral Anticoagulation should be avoided where possible due to altered pharmacokinetics and potential insufficient therapeutic effects following bariatric surgery. Warfarin is preferred over DOACs in patients who require full-dose anticoagulation, since the anticoagulant effect of warfarin can be monitored.

However, bariatric surgery may still affect warfarin absorption, which may be unpredictable.  Monitor the INR and adjust the dose as required.

Endocrine

The effect of bariatric surgery on oral bisphosphonates and antidiabetic medicines is considered. Other endocrine medicines may also be affected.

Oral bisphosphonates

There is an increased risk of gastro-intestinal adverse effects, including damage to the gastro-intestinal mucosa, therefore oral bisphosphonates should be avoided where possible.

However, patients who have undergone bariatric surgery may also be at an increased risk of osteoporosis. Consider other therapies where clinically suitable. Intravenous bisphosphonates can also be considered.

Antidiabetics

Bariatric surgery may affect the absorption of antidiabetic medicines, so it is important to monitor blood glucose and adjust doses accordingly.

Changes to food intake and weight are also likely to require dose adjustments.

Gastrointestinal

The effect of acid suppression on weight loss is considered.

Acid suppression

Most patients will be prescribed a proton pump inhibitor following bariatric surgery.

The use of acid suppressive agents may lead to a delay in achievement of peak weight loss following surgery. It is not currently known why this occurs. The extent of weight loss in the long-term does not appear to be affected

Mental health

Since absorption of medicines may be affected, patients should be closely monitored for worsening of symptoms, with more regular assessments taking place.

Dose adjustments, or switching to alternative therapies, may be required.

Antipsychotics

Given the limited data on pharmacokinetic changes after surgery, routinely switching to depot antipsychotics is not recommended. However this may be an option in patients demonstrating signs of reduced bioavailability and worsening of symptoms.

Bariatric surgery may contribute to additional cardiac stress, and this may be relevant in patients with QT-prolongation, especially if they are on antipsychotics which affect the QT-interval.

Lithium

Lithium toxicity has been reported with some types of bariatric surgery (for example Roux-en-Y gastric bypass and sleeve gastrectomy). Lithium plasma levels can be affected by dietary changes, malabsorption, fluid alterations and weight loss.

Patients will therefore need to be closely monitored. Switching to equivalent dose of lithium citrate solution can be considered.

Neurology

The effect of bariatric surgery on antiseizure medicines is considered.

Antiseizure medicines

The absorption of antiseizure medicines may be reduced following some bariatric surgeries, particularly with controlled release or enteric coated formulations.

Switching to liquid preparations may need to be considered. It might also be better to make this switch before the surgery is undertaken.

The patient should be monitored closely for changes in clinical efficacy and adverse effects. Doses should be adjusted accordingly.

Obstetrics and Gynaecology

Contraception and bariatric surgery is considered.

Contraceptives

It is important that a discussion about contraception takes place before bariatric surgery. This should include if contraception needs to be stopped prior to the surgery, and a plan for contraception after surgery.

The effectiveness of oral contraception (OC), including oral emergency contraception (EC), could be reduced by bariatric surgery. This is due to various mechanisms, but includes a potential reduction in enterohepatic circulation, and chronic diarrhoea following long-term complications of surgery. Non-oral contraception methods are therefore recommended.

Effective and reliable contraception is important following the first 2 years after bariatric surgery. Pregnancy should be avoided during this period of intense weight loss and additional complications may occur. The UK Medical Eligibility Criteria  (UKMEC) advises that a long-acting reversible contraception (LARC) method should be considered during this time, since this is the most effective.

Ongoing high Body Mass Index (BMI), and the bariatric surgery itself, increase the risk of venous thromboembolism. Oestrogen containing contraception should therefore be avoided. If a hormonal method is required, a levonorgestrel-releasing intrauterine device, or a progesterone-only implant, may be a preferred option.

A reduction in weight following surgery may also lead to increased fertility.

Pain

Analgesic requirements will need to be managed. This includes during the acute phase after surgery, and any underlying longer term conditions.

Absorption, and therefore clinical efficacy of analgesics, may be affected following bariatric surgery. However, peak plasma concentrations may be achieved quicker, and reduced dosing may therefore be required.

The absorption of modified-release preparations may also be affected by some bariatric surgeries

Non-Steroidal Anti-inflammatory Drugs

Non-steroidal anti-inflammatory drugs (NSAIDs) should be avoided as a precaution, since patients may be at increased risk of gastro-intestinal bleeding and ulcers following bariatric surgery.

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