The alpha-1 adrenergic receptor antagonists (also called alpha-blockers) are a family of agents that bind to and inhibit type 1 alpha-adrenergic receptors and thus inhibit smooth muscle contraction. Their major uses are for hypertension and for symptomatic benign prostatic hypertrophy. Their use in therapy of hypertension is based on the inhibition of vascular resistance in arterioles from alpha-adrenergic blockade, which results in an increase in venous capacitance and lowering of blood pressure. At present, however, the alpha-1 adrenergic antagonists are recommended only as adjunctive therapy of hypertension and not as monotherapy. Postural hypotension is particularly common after the initial dose of the alpha-1 adrenergic antagonist. Also, long term therapy has not been associated with improvement in survival; indeed at least one study has shown an increase in heart failure, stroke and cardiovascular disease with long term therapy with alpha-blockers. Because the nonselective alpha-1 adrenergic antagonists cause a relaxation of smooth muscle both in arterioles (alpha-1b receptors) and in the bladder neck and prostate (alpha-1a receptors), they are also useful in the therapy of symptoms of urinary obstruction due to benign prostatic hypertrophy. Recently, selective alpha-1a adrenergic receptors blockers have been developed for use in benign prostatic hypertrophy that are claimed to have less effect on blood pressure. Thus, only the nonselective agents are used for treatment of hypertension, whereas both selective and nonselective agents have been used for the symptomatic relief of prostatic hypertrophy.
The nonselective alpha-1 adrenergic antagonists in clinical use for hypertension in the United States include three agents of similar chemical structure (piperazinyl quinazolines) and activity, but somewhat different potencies and pharmacokinetics: prazosin (Minipress: 1976), terazosin (Hytrin: 1987), and doxazosin (Cardura: 1990). These agents, which are used in the treatment of hypertension, are discussed elsewhere.
The alpha-1 adrenergic antagonists in clinical use for benign prostatic hypertrophy and symptoms of urinary hesitancy in the United States include three nonselective agents – terazosin and doxazosin (see Antihypertensive Agents drug records) and alfuzosin (Uroxatral: 2003), and two selective alpha-1a adrenergic receptor antagonists – tamsulosin (Flomax: 2007) and silodosin (Rapaflo: 2008). The selective agents have the potential of reducing bladder neck tone with less risk of hypotension.