Pharmacokinetics of bisoprolol and influence on serum thyroid hormones in hyperthyroid patients

Nine hyperthyroid patients (FT4 greater than or equal to 20 ng/L; FT3 greater than or equal to 6 ng/L) were given 1 X 10 mg bisoprolol/day p.o. for a period of 7 days. Pharmacokinetic data were derived from measurements of plasma bisoprolol concentrations after the first dose and at steady state after 7 days treatment. The thyroid hormones FT4, FT3, and rT3 were determined in the serum before and after bisoprolol treatment. In addition, subjective and objective parameters of thyroid function were recorded during the course of the therapy. The maximum bisoprolol concentrations measured after the first dose and after 7 days were 54.3 +/- 2.1 and 70.3 +/- 3.8 ng/ml, respectively, the minimum concentrations being 9.6 +/- 1.0 ng/ml and 11.9 +/- 1.7 ng/ml, respectively. This yields an accumulation factor of 1.2. At steady state, the plasma elimination half-life of bisoprolol was 9.8 +/- 0.9 h. No significant changes in serum thyroid hormones were observed during bisoprolol treatment. There was, however, an improvement in the subjective and objective clinical symptoms of hyperthyroidism. In comparison with the findings in healthy volunteers, the pharmacokinetics of bisoprolol remained unaltered in mild to moderate hyperthyroid patients. After oral application of bisoprolol, only small variations in the plasma concentration were observed inter- and also intraindividually in the course of treatment. This finding reflects the high absolute bioavailability of bisoprolol.