Problems of anticoagulation with warfarin in hyperthyroidism.
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 patients 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.
H A
HA
Kellett
J S
JS
Sawers
F E
FE
Boulton
S
S
Cholerton
B K
BK
Park
A D
AD
Toft
D000368:Aged; D001777:Blood Coagulation / Q000187:drug effects*; D005167:Factor VII / Q000378:metabolism; D005260:Female; D006801:Humans; D006980:Hyperthyroidism / Q000097:blood*; D008875:Middle Aged; D010314:Partial Thromboplastin Time; D011516:Prothrombin / Q000378:metabolism; D011517:Prothrombin Time; D014859:Warfarin / Q000009:adverse effects*
D014859:Warfarin; D005167:Factor VII; D011516:Prothrombin