SFEBES2009 Poster Presentations Thyroid (59 abstracts)
Levothyroxine and iron in pregnancy: right dose, wrong time?
JM Ng 2 , A Wakil 2 , A Dawson 2 , EA Masson 2 , BJ Allan 2 , SW Lindow 1 , R Krishnan 1 , S Wardell 1 & Y Igzeer 1
1Womens and Childrens Department, Hull, UK; 2Diabetes Centre, Hull, UK.
Background: Absorption of levothyroxine is significantly reduced in the presence of oral iron if these two medications are ingested simultaneously, possible as a result of the formation of an insoluble complex with these 2 medications. Ideally all hypothyroid pregnant women on thyroid replacement therapy should be advised to avoid simultaneous ingestion of levothyroxine and iron containing medicines.
Patients and methods: We conducted a retrospective observational analysis of all hypothyroid pregnant women attending our joint obstetric endocrine clinic who had a successful pregnancy between May and August 2008. Eighteen women already on levothyroxine were included. Seven women were also on iron containing medications while 11 were only taking levothyroxine. Levothyroxine dose, TSH results, medical history and drug history was obtained by discerning clinic notes. Comparison of TSH level and levothyroxine dose in the two groups was done using Mann–Whitney Test.
Results: There was no difference in thyroid stimulating hormone (TSH) between the two groups. (P=0.26) However a significant increase in dosage of levothyroxine was seen in patients taking iron supplements. Forty percent in patients taking iron versus 13% in patients not taking iron; P<0.05. All patients did not have any other significant medical history and were not on any other medications that would impair levothyroxine absorption.
Conclusion: Ingesting thyroid and iron tablets simultaneously has resulted in the need to increase the dose of thyroxine to achieve the same thyrotrophin level. All hypothyroid women should be educated regarding potential interaction between iron tablets and thyroxine.
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Endocrine Abstracts
ISSN 1470-3947 (print) | ISSN 1479-6848 (online)
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