Biomedical subjects
C P Ryan
Publications and source records attributed to C P Ryan.
Recurrent trichophytobezoar in a cat.
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Bilateral nephrolithiasis in a cat.
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Exacerbation of warfarin-induced anticoagulation by hyperthyroidism.
OBJECTIVE: To alert clinicians to the potential interaction between warfarin and hyperthyroidism. METHODS: We present two case reports and compare findings with those in a control population of patients with hyperthyroidism who were not receiving anticoagulant therapy. RESULTS: In two patients, severe coagulopathy was precipitated by the interaction of warfarin and increased thyroid hormone levels. In both cases, the patients also demonstrated resistance to vitamin K therapy, which persisted for several days. We also studied five control patients with hyperthyroidism who were not taking anticoagulant drugs; no effect of thyroid hormone on the plasma levels of vitamin K-dependent clotting factors was noted. One of our patients with hyperthyroidism who was taking warfarin had levels of warfarin in the serum that were 5 times the therapeutic range; this finding suggests that the protein binding or absorption of warfarin may be altered in such patients. CONCLUSION: Multiple factors may contribute to the enhanced effect of warfarin seen in patients with hyperthyroidism, including altered metabolism of vitamin K-dependent clotting factors, altered metabolism of warfarin, or decreased protein binding of the drug. Patients with hyperthyroidism should be given lower doses of warfarin to avoid severe coagulopathy.