Plasma Concentration and Antihypertensive Effect of <i>&beta;</i>-Receptor Blockers

Prof. G. Hitzenberger, Division of Clinical Pharmacology, Medical Clinic of the University of Vienna Medical School, A-1090 Vienna (Austria) In the past years, several attempts have been made to correlate dosage, plasma concentration and effect of certain drugs to their pharmacological activity. Among others, such attempts have also been made with /3-receptor antagonists. Whereas Zacest and Koch-Weser (1972) found a linear relationship of |3-blockade to the logarithm of the plasma concentration of propranoloi, Sundquist et al. (1974) could not find any correlation between the dosage and serum concentration of practolol on one hand, and a reduction of both systolic and diastolic blood pressure and of heart rate in patients with mild to moderate hypertension on the other. In order to test patient compliance and to compare the antihypertensive effect and the reduction in heart rate, due to j3-receptor blockers, to blood levels, the plasma concentrations of propranoloi, oxprenolol and timolol were measured in three groups of patients with mild to moderate hypertension. These measurements were carried out gas-liquid-chromatographically, according to the method of Jack and Riess (1974), modified by Horwatitsch (unpublished method). 20 patients treated in our out-patient clinic with propranoloi and 18 patients treated with oxprenolol and 6 patients treated with timolol were examined. Blood was drawn casually in the morning approximately 2–3 h after the reported ingestion of the drug, and the concentrations were compared to the reduction in systolic and diastolic blood pressure and in heart rate regarding the blood pressure and heart rate values before the beginning of treatment. Since the number of patients on timolol was too small to evaluate the results statistically the following tables and graphs will only show the results with propranoloi and with oxprenolol. Figures 1 and 2 show the correlation /3-Receptor-Blocker – Hypertension 15 Fig. 1. Correlation between daily dose of propranolol and plasma concentration. Fig. 2. Correlation between daily dose of oxprenolol and plasma concentration. Hitzenberger 16