The influence of age, smoking and hyperthyroidism on plasma propranolol steady state concentration.

1 Plasma propranolol steady state concentration (Css) was determined during chronic dosage (160 mg/day) in 22 hyperthyroid patients (aged 16-75 years, 11 smokers, 11 non-smokers) and again following treatment when euthyroid. 2 There was a positive correlation between plasma propranolol Css and age in patients both when hyperthyroid (r = 0.74, P less than 0.01) and when euthyroid (r = 0.58, P less than 0.05). 3 Plasma propranolol Css in hyperthyroid patients were lower (P less than 0.05) in smokers than in non-smokers. 4 Following correction of hyperthyroidism there was a significant increase (P less than 0.01) in both the plasma propranolol Css and degree of plasma protein binding of propranolol. 5 Hyperthyroidism and smoking are known to increase the rate of drug metabolism and it is suggested that these variables may give rise to or accentuate an age related reduction in propranolol clearance.