PROBLEMS OF ANTICOAGULATION WITH WARFARIN IN HYPERTHYROIDISM

  • 1 January 1986
    • journal article
    • research article
    • Vol. 58  (225) , 43-51
Abstract
From clinical observation it would appear that hyperthyroid patients are particularly sensitive to the anticoagulant effects of warfarin. A study was made of clotting factors prothrombin (II), VII, procoagulant VIII (VIIIC), IX and X and of prothrombin ratio (PTR) and partial thromboplastin time with kaolin (PTT-K). These parameters and warfarin levels were measured before and following a single dose of warfarin given to five paitents when hyperthyroid and again when euthyroid. Hyperthyroidism was associated with lower activity of factor II and a shorter PTT-K. Warfarin produced a greater fall in factors II and VII and a greater increase in PTR and PTT-K in the hyperthyroid state than in the euthyroid state. The enhanced response to warfarin in hyperthyroidism was, however, relatively greater for the PTR than for the PTT-K. In order to produce adequate protection against intravascular thrombosis by a suitable prolongation of the PTT-K, it may be necessary in hyperthyroid patients to extend the PTR beyond the normal therapeutic range.

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