As a clinical pharmacist, you should advice your patient that It's important to take levothyroxine FIRST THING in the morning on an empty stomach, because absorption can be decreased by calcium, iron, fiber, and other substances.
New evidence suggests that even coffee MIGHT reduce absorption. Tell patients to wait at least 30 mins before eating, and 4 hrs before taking supplements with calcium, iron, magnesium, or aluminum. The same 4-hour wait goes for sucralfate, cholestyramine, and orlistat. For patients who are not willing to wait, suggest at least being consistent each day, so they get a consistent dose.
Don't let patients get so concerned about the proper timing that they fail to take their levothyroxine. Explain that it's more important to take it than to take it at the perfect time.
REFERENCES
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Benvenga S, Bartolone L, Pappalardo MA, Russo A, Lapa D, Giorgianni G, Saraceno G, Trimarchi F. Altered intestinal absorption of L-thyroxine caused by coffee. Thyroid. 2008 Mar;18(3):293-301. Available at: https://pubmed.ncbi.nlm.nih.gov/18341376
Singh N, Singh PN, Hershman JM. Effect of calcium carbonate on the absorption of levothyroxine. JAMA. 2000 Jun 7;283(21):2822-5. Available at: https://jamanetwork.com/journals/jama/fullarticle/192748
Mazokopakis EE, Giannakopoulos TG, Starakis IK. Interaction between levothyroxine and calcium carbonate. Can Fam Physician. 2008 Jan;54(1):39. Available at: https://pubmed.ncbi.nlm.nih.gov/18208953
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