[Pharmacokinetics of digoxin in hyperthyroidism. Effect of methimazole].

INTRODUCTION

Cardiovascular abnormalities may be the only manifestations of overt hyperthyroidism. In patients with heart failure and atrial fibrillation digoxin can be beneficial in controlling the symptoms and signs, but hyperthyroid patients show an impaired response or even resistance to digoxin treatment. The aim of the study is to establish: 1. Are there any differences in the pharmacokinetics of a single oral dose of digoxin between hypertyroid and euthyroid patients? 2. Does simultaneous administration of digoxin and methimazole affect the pharmacokinetics of a single oral dose of dogoxin? 3. Does methimazole-induced euthyroidism change the pharmacokinetics of a single oral dose of digoxin?

MATERIAL AND METHODS

The subject of the study were 28 patients with hyperthyroidism and 15 healthy persons. We evaluated the pharmacokinetics of a single oral dose of digoxin. Moreover we evaluated pharmacokinetics of a single dose of digoxin after simultaneous administration of digoxin and methimazole in 12 patients and 12 methimazole treated patients werere-assessed once they had become euthyroid.

RESULTS

Hyperthyroid patients showed significantly lower serum digoxin concentrations, shorter T1/2 beta and a significantly smaller area under the concentration curve (AUC) that the control group. Administration of methimazole did not affect digoxin pharmacokinetics.

CONCLUSIONS

In hyperthyroid patients: 1. the pharmacokinetics of a single oral dose of digoxin does differ from that observed in healthy subjects. 2.methimazole do not alter digoxin pharmacokinetics.