The acute and chronic hypotensive effect of labetalol and the relationship with pretreatment plasma noradrenaline levels.

1 Labetalol 100 mg was given intravenously to 27 patients with essential hypertension (12 males, 15 females; WHO I-II; age range 30-66 yr; on average, a significant reduction of blood pressure was observed within 5 min (P less than 0.001). Average heart rate was also reduced significantly (P less than 0.01). 2 In 18 patients haemodynamic measurements were performed (dye-dilution or thermodilution technique): blood pressure reduction was related to peripheral vasodilatation, as cardiac index remained unmodified. 3 The absolute and percentage decrease of blood pressure, heart rate and total peripheral resistance after labetalol 100 mg intravenously, was significantly greater in the patients with higher baseline plasma noradrenaline concentration values. 4 In 12 out of 27 patients labetalol was given orally for 2 months (dose range 300-1200 mg); the pattern of blood pressure and heart rate changes after oral therapy were comparable to those observed after acute administration of the drug. 5 The degree of blood pressure and heart rate reductions after oral labetalol was also significantly related to pretreatment basal noradrenaline concentration.