Yair Liel, MD
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Liel Y. Levothyroxine Therapy. Ann Intern Med. 1994;120:619-620. doi: 10.7326/0003-4819-120-7-199404010-00017
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Published: Ann Intern Med. 1994;120(7):619-620.
TO THE EDITOR:
In the review by Mandel and colleagues  on levothyroxine therapy, activated charcoal was omitted from the list of conditions affecting levothyroxine requirements by interfering with intestinal absorption . By contrast, evidence in favor of interference with levothyroxine pharmacokinetics by lovastatin is weak .
The suggestion to separate by at least 3 hours the administration of levothyroxine from administration of medications that may interfere with its intestinal absorption could be risky because thyroxine undergoes enterohepatic circulation . In our experience, separating the administration of an aluminum hydroxide from that of levothyroxine does not prevent considerable increase in serum levels of thyroid-stimulating hormone (TSH) . Administration of levothyroxine and cholestyramine produced a marked increase in serum TSH in another patient, despite a minimum 4-hour separation between times of ingestion. I strongly agree with the suggestion to monitor thyroid function tests 1 month after initiation (or cessation) of drugs that affect levothyroxine requirements.
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Print ISSN: 0003-4819 | Online ISSN: 1539-3704
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