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Obesity - Management
What important interactions are associated with orlistat?

  • If fat-soluble vitamins or multivitamin supplements are taken, they should be given at least 2 hours after a dose of orlistat or at bedtime.
  • Orlistat reduces plasma levels of ciclosporin. If concomitant use is unavoidable, ciclosporin levels should be monitored frequently, both after initiation of orlistat and on discontinuation [Baxter, 2006].
  • Orlistat may reduce the absorption of levothyroxine, leading to reduced control of hypothyroidism [MHRA, 2010]. Consider taking levothyroxine at a different time to orlistat to reduce the interaction (such as 2 hours after a dose of orlistat or at bedtime).
  • Orlistat may also reduce the absorption of antiepileptic drugs. Loss of seizure control has been reported during concomitant treatment with orlistat and sodium valproate or lamotrigine [MHRA, 2010]. Consider taking antiepileptic drugs at a different time to orlistat to reduce the interaction (such as 2 hours after a dose of orlistat or at bedtime).
  • Orlistat may reduce the absorption of fat-soluble vitamin K, with the result that a lower dose of warfarin is required. In people taking warfarin, the international normalized ratio (INR) should be monitored closely, especially when starting or stopping treatment with orlistat [Micromedex, 2007].
  • No direct interaction between oral contraceptives and orlistat has been demonstrated in specific drug-drug interaction studies. However, orlistat may indirectly reduce the availability of oral contraceptives through its action on the gastrointestinal tract. If a woman experiences severe diarrhoea whilst taking orlistat an additional contraceptive method is recommended [ABPI Medicines Compendium, 2006].

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