Prazosin

Mechanism of Action

(Selective a1 blocker).

Pharmacological Effects

V.D. of arteries and veins lowering the blood pressure.  

Therapeutic Uses

1. Treatment of mild to moderate hypertension.
2. Treatment of acute congestive heart failure (decreases pre- and after-load).
3. Impaired bladder emptying due to prostate obstruction (decreased the tone of trigone) *leads to decreased resistance to flow of urine. (tamsulosin) a1 blocker potentates relaxation of sphincter; symptomatic treatment’
4. Peripheral vascular disease (Raynaud’s disease)

Adverse Effects

First dose effect: (to avoid, give small initial dose rather than full dose & avoid diuretics)

1. The initial dose especially if large can produce postural hypotension and syncope. - It occurs most commonly in salt and water depleted patients (start with a small dose and at bedtime).
2. Dizziness, headache, drowsiness, and palpitation (disappears with continued treatment).
3. False positive tests for antinuclear factor.
4. Salt and water retention. (all drugs cause this except diuretics)
5. Flushing , ,Nasal congestion, Failure of ejaculation in males.

 TERAZOSIN , alfuzosin and TRIMAZOCIN  Similar to prazosin but it does not produce first-dose syncope.