Interdose control of beta-blockade and arterial blood pressure during chronic oral labetalol treatment.

1 The pharmacological and therapeutic effects of labetalol were investigated during an 8 h interdose period of chronic oral therapy in six patients with essential hypertension. 2 Peak plasma labetalol concentrations were observed 2 h after the morning oral dose, and subsequent decline was mono exponential. 3 Beta-adrenoceptor blockade paralleled the changes in labetalol concentration and was maximal 2 and 4 h after the oral dose. 4 Resting supine systolic BP rose significantly during the interdose period, but no change occurred in diastolic BP. 5 Ambulatory intra-arterial BP studies in a further six patients with essential hypertension controlled with labetalol did not confirm the increase in BP during an 8 h interdose period.