Alpha-adrenoceptor antagonists

General information

The postsynaptic alpha-adrenoceptor antagonists, indoramin, prazosin, and related quinazoline derivatives, block alpha1-adrenoceptor-mediated vasoconstriction of peripheral blood vessels (both arterial and venous) and are effectively peripheral vasodilators [ , ]. Qualitatively and quantitatively common adverse effects are generally similar, although indoramin has additional effects on other neurotransmitter systems and therefore tends to be considered separately. Their use in benign prostatic hyperplasia has been reviewed [ , ].

Several recent articles have reviewed the pharmacology, pharmacokinetics, mode of action, use, efficacy, and adverse effects of the selective alpha1-adrenoceptor blockers doxazosin, prazosin, and terazosin in benign prostatic hyperplasia [ ].

The frequencies and the profile of adverse effects of five major classes of antihypertensive agents have been assessed in an unselected group of 2586 chronically drug-treated hypertensive patients [ ]. This was accompanied by a questionnaire-based survey among patients attending a general practitioner. The percentage of patients who reported adverse reactions spontaneously, on general inquiry, and on specific questioning were 16%, 24%, and 62% respectively. With alpha-blockers the figures were 15%, 25%, and 50%. The percentage of patients in whom discontinuation was due to adverse effects was 6.8% with alpha-blockers. Alpha-blockers were associated with less fatigue, cold extremities, sexual urge, and insomnia, and more bouts of palpitation than other antihypertensive drugs (RR = 2.5; CI = 1.2, 5.4). The authors did not find a significant effect of age on the pattern of adverse effects. Women reported more effects and effects that were less related to the pharmacological treatment.

The first-dose effect (profound postural hypotension and reflex tachycardia) is a well-recognized complication of the first dose of prazosin and related agents. This phenomenon is dose-related and can usually be avoided by using a low initial dosage taken at bedtime. During long-term treatment, orthostatic hypotension and dizziness is reported by about 10% of patients.

Guidelines on the use of postsynaptic alpha-adrenoceptor antagonists have been reviewed [ ].