Review of long-term treatment with labetalol.

1 Labetalol has been used to treat 163 patients at the Dunedin Hypertension Clinic for periods up to 6.5 y, and of 128 patients in a New Zealand multicentre study for 2 yr. 2 Labetalol was often effective when other anti-hypertensive agents, including beta-blockers, had failed. It was usually given with a diuretic. 3 Mean daily dose was 700 mg (range 100-2400 mg). No tolerance to the anti-hypertensive effect was seen. 4 Some postural-induced decrease in blood pressure on labetalol was common. 5 Side-effects led to withdrawal of labetalol in about 25% of patients, mainly during the first few months of therapy. Another 25% had minor side-effects but could continue with the drug. 6 There were three types of side-effects (in order of frequency): (a) non-specific, (b) related to alpha-blockade and (c) related to beta-blockade. The latter were much less troublesome than on "pure" beta-blockers. 7 There was no significant evidence of renal haematological or hepatic toxicity. 8 Anti-nuclear antibody tests became positive on labetalol in about 15%, usually at low titres but in one patient the titre increased to a high level and fell when labetalol was stopped. 9 In a subset of 25 patients who took labetalol for the longest time (up to 6.5 yr) there was a 16% incidence of anti-mitochondrial antibodies.