ATC Group: G04CA Alpha-adrenoreceptor antagonists

Alfuzosin is an orally active quinazoline derivative. It is a selective, peripherally acting antagonist of postsynaptic alpha-1-adrenoceptors. In vitro pharmacological studies have documented the selectivity of alfuzosin for the alpha-1-adrenoreceptors located in the prostate, bladder base and prostatic urethra.

Silodosin is highly selective for α_1A-adrenoreceptors that are primarily located in the human prostate, bladder base, bladder neck, prostatic capsule and prostatic urethra. Blockade of these α_1A-adrenoreceptors causes smooth muscle in these tissues to relax, thus decreasing bladder outlet resistance, without affecting detrusor smooth muscle contractility.

Tamsulosin binds selectively and competitively to post-synaptic α₁-adrenoreceptors, prevailingly their subtypes designated α_1A and α_1D. Thus relaxation of smooth muscles of the prostate and urethra is achieved, which leads to a reduction of tonus and an improvement of the urinary flow.

Although the exact mechanism of the hypotensive action is not established, the relaxation of peripheral blood vessels appears to be produced mainly by competitive antagonism of post-synaptic alpha-adrenoceptors. Terazosin usually produces an initial gradual decrease in blood pressure followed by a sustained antihypertensive action.