Labetalol and propranolol in mild hypertensives: comparison of blood pressure and plasma volume effects.

Labetalol administered in a small to moderate dose (first month 400 mg/day, second month average 585 mg/day) was effective in lowering blood pressure (BP) (-21/-18 mmHg, recumbent) in 11 of 13 mild essential hypertensives over an eight-week period, despite a significant (+294 ml) increase in plasma volume. The effect of propranolol (first month 160 mg/day, second month average 234 mg/day) was significantly less on both blood pressure (-9/-9 mmHg) and plasma volume (+98 ml), although the pre-propranolol BP was lower and the final BP achieved on the two medications was comparable (labetalol 147/89 mmHg, propranolol 145/89). Six patients who continued labetalol for periods of up to 14 months had persistent plasma volume expansion. Three of these, taking a higher dose of labetalol, developed resistance to the drug's antihypertensive effect. Addition of a diuretic restored antihypertensive efficacy and led to a fall in plasma volume. No such plasma volume expansion was seen in six patients who were followed on long term propranolol therapy. Some plasma volume expansion with the combined alpha- beta-adrenoceptor blocker labetalol may be appropriate to its vasodilator action. Provided this effect is not excessive, it appears not to lead to resistance to its antihypertensive action. Small to moderate doses of labetalol would, therefore, seem effective without concomitant diuretic. Such sole use of labetalol could help minimise orthostatic symptoms which can be a major side effect of combination therapy.