Prazosin

[PHW2:p212]

 

Quinazoline derivative

Pharmacodynamics

Mechanism of action

[PHW2:p212]

Highly selective alpha1 antagonist

 

Effects

[PHW2:p212]

CVS

Vasodilation
--> Reduced SVR

Little or no reflex tachycardia

Decreased BP
* Diastolic pressure falls more

 

Urinary

Relaxation of the bladder trigone and sphincter muscle
--> Improvement of urine flow in benign prostatic hypertrophy

Impotence and priapism have been reported

 

CNS

Fatigue

Headache

Vertigo

Nasuea

 

Others

May produce false-positive when screen urine for metabolites of noradrenaline (VMA and MHPG, as seen in phaeochromocytoma)

 

Pharmacokinetics

Variable oral availability 50-80%

 

Highly protein-bound
* Mainly to albumin

 

Extensively metabolised in liver
* Demethylation and conjugation

Some active metabolites

 

Plasma half-life = 3 hours

Largely excreted in the bile
* May be used safely in renal impairment

Time to peak level = 90 min after oral dose

 

 

 

Clinical

Usage

[PHW2:p212]

Used in treatment of

Essential hypertension

Congestive heart failure

Raynaud's syndrome

Benign prostatic hypertrophy