DISPOSITION KINETICS AND CONCENTRATION-EFFECT RELATIONSHIP OF METIPRANOLOL IN PATIENTS WITH CIRRHOSIS AND HEALTHY-SUBJECTS

The disposition kinetics and heart rate reducing effect of deacetylmetipranolol (DMP), the active form of the beta-adrenoreceptor blocking agent metipranolol (MP), administered as a single 40 mg oral dose have been compared in 6 patients with cirrhosis and 6 healthy volunteers. The mean maximal DMP concentration was significantly higher and the time to reach the peak level shorter in the patients compared to the healthy subjects. There was also a significantly higher AUC of DMP, a shorter half-life of the rapid phase of the decline in DMP concentrations, a smaller central compartment and lower apparent DMP clearance in patients. A correlation with the albumin level was observed in cirrhotics for individual values of apparent DMP clearance (r = 0.92) and AUC (r = -0.89). The maximal reduction in heart rate was recorded in patients at plasma DMP levels which were already significantly lower than the peak levels. Median inhibitory concentrations (IC50) and maximum possible heart rate reductions (DELTA-HR(max)), obtained by fitting individual plots of the plasma DMP concentration-effect relationship to the inhibitory E(max) model in the postdistributional phase of DMP disposition were significantly higher in cirrhotics than in healthy subjects. It is conjectured that down-regulation of adrenoreceptors due to chronic sympathetic activation in hepatic cirrhosis contributes to decreased sensitivity to the reduction in heart rate following a single dose of the beta-blocker.