In late March, 2009, the FDA approved safety labeling revisions for levothyroxine sodium tablets (i.e., Synthroid, Levoxyl, etc.) to advise of drug interactions with orlistat. Levothyroxine's prescribing information will now include a warning that indicates that use of orlistat may decrease levothyroxine absorption and lead to hypothyroidism, and that clinicians are advised to administer levothyroxine and orlistat at least 4 hours apart and to perform regular evaluations of thyroid function.
Xenical's prescribing information (PDF) has already been revised to reflect the potential interaction between orlistat and levothyroxine. Specifically:
- Under "Drug Interactions," they have added "Hypothyroidism has been reported in patients treated concomitantly with orlistat and levothyroxine"
- Under "Adverse Reactions / Other Clinical Studies or Postmarketing Surveillance," they have added, "Hypothyroidism has been reported in patients treated concomitantly with orlistat and levothyroxine."
- Under "Can I take XENICAL while taking other medications?" they have added "XENICAL and levothyroxine should be taken at least 4 hours apart"