Endocrine Abstracts

Hyperthyroid patients show an impaired response or even resistance to digoxin treatment.

Objectives: 1. Are there any differences in the pharmacokinetics of a single oral dose of digoxin between hyperthyroid and euthyroid patients? 2. Does simultaneous administration of digoxin and methimazole or digoxin and acebutolol 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? 4. Does acebutolol, which ameliorates symptoms of hyperkinetic circulation change the pharmacokinetics of a single oral dose of dogoxin?

Design and method: 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. Twelve methimazole treated patients were re-assessed once they had become euthyroid. Sixteen acebutolol-treated patients were re-asessed once symptoms of hyperkinetic circulation had subsided.Moreover we evaluated pharmacokinetics of a single dose of digoxin after simultaneous administration of digoxin and methimazole or digoxin and acebutolol.

Results: Hyperthyroid patients showed significantly lower serum digoxin concentrations, shorter T½ beta and a significantly smaller area under the concentration curve that the control group. Administration of methimazole did not affect digoxin pharma-co-kinetics, administration of acebutolol resulted in an increased serum digoxin concentration and in a longer time to the peak serum level of digoxin in comparison with the control group.

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