Evolution of atenolol kinetics when hypothyroidism is corrected.

A single oral dose of atenolol 100 mg was given to 7 hypothyroid patients (4 F, 3 M), before and after correction of hypothyroidism, mean delay 3.5 months (2 to 6.5 months). There was no change in the elimination parameters of atenolol, but the maximal plasma atenolol concentration was increased (1.66 to 7.37 mg.l-1) as was the AUC (14.9 to 52.1 mg.l-1.h) when the hypothyroidism had been treated. Only one patient differed: he had had a supra-selective vagotomy, and had similar curves before and after treatment of the hypothyroidism, both being similar to the plasma concentration curves found in the other patients after correction of the hypothyroidism. The results suggest an increase in the bioavailability of atenolol when hypothyroidism is corrected. The findings in the patient with vagotomy suggest that the decreased bioavailability during hypothyroidism might be related to changes in intestinal pH. Further studies are needed of the impact of hypothyroidism on gastric and pancreatic or biliary function and its consequences for drug absorption, and drug pharmacokinetics.