Pharmacokinetics, beta-adrenoceptor blockade and anti-hypertensive action of labetalol during chronic oral treatment.

1 beta-Adrenoceptor blockade, plasma labetalol concentrations and anti-hypertensive actions were investigated at 2 hourly intervals during the interdose period of chronic oral therapy in six hypertensive patients. 2 beta-adrenoceptor blockade varied during the inter-dose period and was maximal 2 and 4 h after the oral dose (P < 0.05). 3 Systolic pressure rose during the interdose period (P < 0.05). A significant correlation was found between the degree of beta-adrenoceptor blockade and the change in systolic pressure at 2 h after the oral dose. 4 Efficacy of labetalol as a beta-adrenoceptor antagonist and anti-hypertensive drug was assessed 2 h after an oral dose during chronic eight hourly dosage in sixteen hypertensive patients. Pharmacokinetics of labetalol were studied in the same patients. 5 Peak plasma labetalol concentration occurred 2 h after the oral dose and subsequently the plasma concentration declined monoexponentially. 6 The steady state concentration (CSS) of labetalol was correlated significantly with the daily oral dose in mg kg-1, the mid point labetalol concentration (Cmax+Cmin) divided by 2 and the isoprenaline dose ratio-1 at 2 h after the oral dose. 7 No correlation was found between the antihypertensive effect and the CSS ng ml-1 labetalol or between the isoprenaline dose ratio-1 and the CSS labetalol ng ml-1.