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.
(Source: Medscape)
Dr KK Aggarwal
Padma Shri Awardee
President Elect Confederation of
Medical Associations in Asia and Oceania
(CMAAO)
Group Editor-in-Chief IJCP Publications
President Heart Care Foundation of
India
Past National President
IMA
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