Prothrombin, Activated Partial Thromboplastin, and Proteins Induced by Vitamin K Absence or Antagonists Clotting Times in 20 Hyperthyroid Cats Before and After Methimazole Treatment

Abstract

The effect of daily doses of 5-15 mg of methimazole on the platelet count, prothrombin time (PT), activated partial thromboplastin time (APTT), and proteins induced by vitamin K absence or antagonists (PIVKA) clotting time in 20 hyperthyroid cats was determined. No significant (P > .05) difference was found in median platelet count. PT, APTT, or PIVKA clotting time before treatment compared to median values at 2-6 weeks or > or =7-12 weeks of methimazole treatment. No cat had a prolonged APTT at any time. At 2-6 weeks of methimazole treatment, 1 cat each developed thrombocytopenia or prolonged PIVKA clotting time despite initially normal values. Three cats had abnormal coagulation tests (prolonged PT [n = 1] and PIVKA clotting time [n = 3]) before treatment that fluctuated during treatment. Excluding the 3 cats that had abnormal PIVKA clotting time before treatment, prolonged PIVKA clotting time developed in 6% (1/17; 95% confidence interval, 0-28%) cats treated with methimazole for 2-6 weeks. Seemingly. doses of methimazole commonly used to treat hyperthyroidism in cats do not cause alteration in PT and APTT, and only rarely prolong PIVKA clotting time. Nevertheless, abnormal PIVKA clotting time may explain bleeding tendencies unassociated with thrombocytopenia in methimazole-treated hyperthyroid cats.

Feline Hyperthyroidism

“…In a study of 20 cats treated with methimazole, three cats had abnormal coagulation profiles characterized by prolongation of protein induced by vitamin K absence or antagonism (PIVKA) prior to treatment, and one cat developed prolongation of PIVKA bleeding time, unassociated with clinical signs of bleeding, 2 to 6 weeks after treatment (Randolph et al, 2000). In a study of 20 cats treated with methimazole, three cats had abnormal coagulation profiles characterized by prolongation of protein induced by vitamin K absence or antagonism (PIVKA) prior to treatment, and one cat developed prolongation of PIVKA bleeding time, unassociated with clinical signs of bleeding, 2 to 6 weeks after treatment (Randolph et al, 2000).…”

Life-threatening haematological complication occurring in a cat after chronic carbimazole administration

“…However, none of the findings supported this differential diagnosis. The coagulation abnormalities detected in this cat, namely the increased prothrombin time, partial thromboplastin time and fibrinogen serum concentration, 5 together with the immunomediated origin of the anaemia, as confirmed by the positive in-saline agglutination test, seem to indicate the carbimazole toxicity as the most likely cause.…”

“…8 More serious side effects are reported for methimazole, such as hepatopathy, bleeding diathesis (prolonged proteins induced by vitamin K absence or antagonists [PIVKA] clotting time) and marked thrombocytopenia. 5,8 Anaemia, including aplastic anaemia, was reported by Chapman et al, 9 after 3 years of treatment, and also by Weiss in 2006. 10 …”

Safety of orally administered,USP‐compliant levothyroxine sodium tablets in dogs

“…In healthy volunteers given 250 μg/day for 8 weeks, the resultant biochemical thyrotoxicosis induced increased expression of numerous procoagulant clotting factors and decreased fibrinolytic factors (Engelmann et al., ). There were no changes in PT, APTT, and PIVKA (Proteins Induced by Vitamin K Absence or Antagonists) values in hyperthyroid cats before and after treatment with methimazole (Randolph et al., ). The mild decrease in mean APTT in the 2× and 6× groups is consistent with the findings in humans.…”