Orlistat drug interactions: what the label says

The label says vitamin K absorption may be decreased with orlistat, and that there have been reports of decreased prothrombin, increased INR and unbalanced anticoagulant treatment resulting in changes to haemostatic parameters in people taking orlistat and anticoagulants together. Its instruction is that patients on chronic stable doses of warfarin or other anticoagulants who are prescribed orlistat should be monitored closely for changes in coagulation parameters. The Alli label lists anticoagulants — blood thinning medicine — among the prescription medicines to raise with a doctor or pharmacist first.

The label reports a pharmacokinetic study in which amiodarone was given orally during orlistat treatment, and exposure to amiodarone and its metabolite desethylamiodarone was reduced. It says a reduced therapeutic effect of amiodarone is possible, and notes that starting orlistat in people already on stable amiodarone therapy has not been studied. Amiodarone — described as heart medicine — is named on the Alli Drug Facts label as one to ask about before use.

The Xenical label says convulsions have been reported in patients treated concomitantly with orlistat and antiepileptic drugs, and that patients should be monitored for possible changes in the frequency or severity of convulsions. The Alli label reflects the same concern in its stop-use section: it says to stop use and ask a doctor if you are taking medicine for seizures and your seizures happen more often or get worse.

The label says loss of virological control has been reported in HIV-infected patients taking orlistat with antiretroviral drugs including atazanavir, ritonavir, tenofovir disoproxil fumarate, emtricitabine, and the combinations lopinavir/ritonavir and emtricitabine/efavirenz/tenofovir disoproxil fumarate. It says the exact mechanism is unclear but may involve inhibited systemic absorption of the antiretroviral drug, that HIV RNA levels should be monitored frequently, and that orlistat should be discontinued if there is a confirmed increase in HIV viral load. The Alli label names antiretrovirals among the prescription medicines to ask about first.

The label says weight loss may affect glycaemic control in people with diabetes, and that a reduction in the dose of oral hypoglycaemic medication, such as a sulfonylurea, or of insulin may be required in some patients. The Alli label lists diabetes medicine among the prescription medicines to discuss with a doctor or pharmacist before use, noting that some prescription doses may need to be adjusted or may not work as well when used with orlistat.