The effect of thyroid function on the prothrombin time response to warfarin in rats

Lowenthal, Julius; Fisher, Lyman M.

doi:10.1007/bf02157446

Cited by 16 publications

(2 citation statements)

References 3 publications

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“…Hyperthyroidism has been shown to increase sensitivity to the hypoprothrombinemic effect of warfarin, requiring lower dosages of the drug for therapeutic effect [5, 6]. Hyperthyroidism causes an increase in both the production and catabolism of vitamin K-dependent clotting factors (II, VII, IX, and X) [7].…”

Section: Introductionmentioning

confidence: 99%

Graves’ Disease and Treatment Effects on Warfarin Anticoagulation

Howard-Thompson

Luckey

George

et al. 2014

Case Reports in Medicine

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Background. Hyperthyroidism causes an increased hypoprothrombinemic response to warfarin anticoagulation. Previous studies have demonstrated that patients with hyperthyroidism require lower dosages of warfarin to achieve a therapeutic effect. As hyperthyroidism is treated and euthyroidism is approached, patients may require increasing warfarin dosages to maintain appropriate anticoagulation. We describe a patient's varying response to warfarin during treatment of Graves' disease. Case Presentation. A 48-year-old African American female presented to the emergency room with tachycardia, new onset bilateral lower extremity edema, gradual weight loss, palpable goiter, and generalized sweating over the prior 4 months. She was admitted with Graves' disease and new onset atrial fibrillation. Primary stroke prophylaxis was started using warfarin; the patient developed a markedly supratherapeutic INR likely due to hyperthyroidism. After starting methimazole, her free thyroxine approached euthyroid levels and the INR became subtherapeutic. She remained subtherapeutic over several months despite steadily increasing dosages of warfarin. Immediately following thyroid radioablation and discontinuation of methimazole, the patient's warfarin dose and INR stabilized. Conclusion. Clinicians should expect an increased response to warfarin in patients with hyperthyroidism and close monitoring of the INR is imperative to prevent adverse effects. As patients approach euthyroidism, insufficient anticoagulation is likely without vigilant follow-up, INR monitoring, and increasing warfarin dosages.

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Section: Introductionmentioning

confidence: 99%

Graves’ Disease and Treatment Effects on Warfarin Anticoagulation

Howard-Thompson

Luckey

George

et al. 2014

Case Reports in Medicine

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“…Although this potential interaction was first described in animal studies more than half a century ago, 28,29 case reports and small prospective studies have done little to expand our understanding of its frequency and clinical relevance. 19,[22][23][24][25][26][30][31][32][33][34] Increases in the international normalized ratio have been observed in clinical settings after patients receiving warfarin became thyrotoxic for various reasons, including after being given levothyroxine.…”

Section: Introductionmentioning

confidence: 99%

A Population-Based Assessment of the Drug Interaction Between Levothyroxine and Warfarin

Pincus

Gomes

Hellings

et al. 2012

Clin Pharmacol Ther

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Most drug interaction resources suggest that levothyroxine can dramatically potentiate the effect of warfarin. However, the mechanistic basis of the interaction is speculative, and little evidence supports a meaningful drug interaction. We conducted a population-based nested case-control study to examine the risk of hospitalization for hemorrhage following the initiation of levothyroxine in a cohort of 260,076 older patients receiving warfarin. In this group, we identified 10,532 case subjects hospitalized for hemorrhage and 40,595 controls. In the primary analysis, we found no association between hospitalization for hemorrhage during warfarin therapy and initiation of levothyroxine in the preceding 30 days (adjusted odds ratio 1.11, 95% confidence interval 0.67-1.86). Secondary analyses using more remote initiation of levothyroxine also found no association. These findings suggest that concerns about a clinically meaningful levothyroxine-warfarin drug interaction are not justified. Drug interaction resources that presently characterize this interaction as important should reevaluate this classification.

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Mechanism of hypoprothrombinemia and hypoproconvertinemia in experimental thyrotoxicosis

Nn¹,

Vi²

1975

Bull Exp Biol Med

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The effect of thyroid function on the prothrombin time response to warfarin in rats

Cited by 16 publications

References 3 publications

Graves’ Disease and Treatment Effects on Warfarin Anticoagulation

Graves’ Disease and Treatment Effects on Warfarin Anticoagulation

A Population-Based Assessment of the Drug Interaction Between Levothyroxine and Warfarin

Mechanism of hypoprothrombinemia and hypoproconvertinemia in experimental thyrotoxicosis

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