Study Set Content:
It is highly selective for a 1 receptors and typically 1000-fold less potent at a 2 receptors. This explain the relative absence of tachycardia seen with prazosin Compared with that of phentolamine and phenoxybenzamine.
PRAZOSIN
Relaxes both arterial and venous vascular smooth muscle, smooth muscle in the prostate, due to blockade of
1 receptors
Prazosin is extensively metabolized by the liver, only about 50% of the drug is available after oral administration. The half-life is normally about
3 hours.
Adverse effects:
Gt hypermotility, orthostatic hypotension, sexual dysfunction, dry mouth, dizziness.
is another reversible a 1 -selective antagonist that is effective in hypertension;
TERAZOSIN
A approved for use in men with urinary symptoms due to
benign prostatic hyperplasia (BPH).
has high bioavailability but is extensively metabolized in the liver, with only a small fraction of unchanged drug excreted in the urine.
Terazosin
The half-life of terazosin is
9-12 hours
is efficacious in the treatment of hypertension and BPH.
Doxazosin
It differs from prazosin and terazosin in having a longer half-life of about
22 hours.
It has moderate bioavailability and is extensively metabolized, with very little parent
• Drug excreted in urine or feces.
Doxasozin
has active metabolites, although their contribution to the drug's effects is probably small
Doxazosin
is a competitive a 1 antagonist with a structure quite different a 1 -receptor blockers
Tamsulosin
It has high bioavailability and a half-life of 9-15 hours. It is metabolized extensively in the
liver.
Has higher affinity for a () than for the 1B subtype
1A AND 1Dsubtype
Has greater potency in inhibiting contraction in prostate smooth muscle versus vascular smooth muscle compared with other a 1 -selective antagonists.
TAMSULOSIN
Patients receiving oral tamsulosin and undergoing cataract surgery are at increased risk of the
intraoperative floppy iris syndrome
characterized by the billowing of a flaccid iris, propensity for iris prolapse, and progressive intraoperative pupillary constriction.
(IFIS),
An a 1-selective quinazoline derivative that is approved for use in BPH.
ALFUZOSIN
It has a bioavailability of about 60%, is extensively metabolized, and has an elimination half-life of about
5 hours
