Orlistat: theoretical interaction with antiretroviral HIV medicines

Initiate orlistat treatment only after careful consideration of the possible impact on efficacy of antiretroviral HIV medicines.

Article date: March 2014

Orlistat is indicated for weight loss in combination with a low-calorie, low-fat diet. It is available as 120 mg capsules under the brand name Xenical and as 60 mg capsules under the brand name alli. Xenical is only available with a prescription, whereas alli is available without a prescription under the supervision of a pharmacist.

Orlistat is a potent, specific, and long-acting inhibitor of gastrointestinal lipases which decreases the amount of fat absorbed from the diet.

On the basis of reports from literature1 2and data obtained after licensing, orlistat may theoretically reduce the absorption of antiretroviral HIV medicines. This may be due to retention of lipophilic medicines in the gastrointestinal tract or reduced gastrointestinal tract transit time. This interaction could negatively affect the efficacy of antiretroviral HIV medications. Reports have been received of suspected interactions between orlistat and efavirenz, and between orlistat and lopinavir. However, the theoretical interaction mechanism described above could also apply to other antiretroviral medicines.

Advice for healthcare professionals:

  • Initiate orlistat treatment only after careful consideration of the possible impact on efficacy of antiretroviral HIV medicines
  • Pharmacists should advise people who take antiretroviral HIV medicines to consult their doctor before taking alli in light of the possible interaction
  • Suspected adverse reactions with orlistat, whether prescribed or obtained over the counter, should be reported to us on a Yellow Card (www.mhra.gov.uk/yellowcard)
  1. de Truchis P et al. AIDS 2010; 24: 1235–36.

  2. Kent SJ. AIDS Res Hum Retroviruses 2012; 28: 961–62.

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