New Delhi, April 16, 2019 ;
Levothyroxine is routinely used as the primary form of thyroid hormone replacement in the management of hypothyroidism. It is absorbed in the small intestine; bioavailability in the euthyroid person is 70-80%.
- Peak absorption is achieved at approximately 2 hours after oral ingestion; this can be delayed to 3-4 hours if it is ingested simultaneously with interfering medications, supplements, or some foods/drinks.
- The American Thyroid Association advise patients to take levothyroxine at least 1 hour before the first meal of the day or at bedtime (at least 3 hours after the evening meal), and at least 4 hours apart from other medications or supplements, if possible.
- Certain conditions have the potential to further reduce the absorption of oral levothyroxine.
- If an individual has known Helicobacter pylori–related gastritis, atrophic gastritis, or celiac disease, a higher dose of levothyroxine may be needed to overcome these malabsorptive states.
- Less is absorbed when it is taken concurrently with substances that include coffee, soy, calcium carbonate, iron, aluminum hydroxide, sucralfate, cholestyramine, colesevelam, raloxifene, orlistat, phosphate binders, or cow’s milk, compared with when levothyroxine is taken alone.
- Interference occurs as a result of physical adsorption (complexing) between the interfering substance and levothyroxine in the gastrointestinal tract.
- Taking levothyroxine together with an interfering substance can decrease the amount of thyroid hormone that is absorbed by as much as 50%, although the degree of this interference has been variable.
The author of this article is Dr KK Aggarwal, Padma Shri Awardee