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Prazosin; Uses, Dosage, Side Effects, Interactions, Pregnancy

Prazosin is a synthetic piperazine derivative and an alpha-1 adrenergic receptor inhibitor used primarily as an anti-hypertensive. Prazosin’s effects are most pronounced in the large resistance vessels (i.e. arterioles) and result in a decrease in total systemic vascular resistance (SVR) without a rebound or reflex tachycardia. To a lesser extent, this agent also decreases the tone of the bladder sphincter, thereby allowing the opening of the bladder into the urethra and thus relieving the urinary conditions associated with benign prostatic hypertrophy.

Prazosin is a sympatholytic drug used to treat high blood pressure, anxiety, and posttraumatic stress disorder (PTSD). It is an α₁-blocker which acts as an inverse agonist at alpha-1 adrenergic receptors. These receptors are found on vascular smooth muscle, where they are responsible for the vasoconstrictive action of norepinephrine. They are also found throughout the central nervous system. Prazosin is a selective α-₁-adrenergic receptor antagonist used to treat hypertension. It has also been used to decrease urinary obstruction and relieve symptoms associated with symptomatic benign prostatic hyperplasia. α₁-Receptors mediate contraction and hypertrophic growth of smooth muscle cells.

Mechanism of Action of Prazosin

Prazosin acts by inhibiting the postsynaptic alpha(1)-adrenoceptors on vascular smooth muscle. This inhibits the vasoconstrictor effect of circulating and locally released catecholamines (epinephrine and norepinephrine), resulting in peripheral vasodilation.Accordingly, Prazosin is a selective inhibitor of the alpha1 subtype of alpha adrenergic receptors. In the human prostate, Prazosin antagonizes phenylephrine (alpha1 agonist)-induced contractions, in vitro, and binds with high affinity to the alpha1c adrenoceptor, which is thought to be the predominant functional type in the prostate. Studies in normal human subjects have shown that Prazosin competitively antagonized the pressor effects of phenylephrine (an alpha1 agonist) and the systolic pressor effect of norepinephrine. The antihypertensive effect of Prazosin results from a decrease in systemic vascular resistance and the parent compound Prazosin is primarily responsible for the antihypertensive activity.

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Prazosin is a synthetic piperazine derivative and an alpha-1 adrenergic receptor inhibitor used primarily as an anti-hypertensive. Prazosin’s effects are most pronounced in the large resistance vessels (i.e. arterioles) and result in a decrease in total systemic vascular resistance (SVR) without a rebound or reflex tachycardia. To a lesser extent, this agent also decreases the tone of the bladder sphincter, thereby allowing the opening of the bladder into the urethra and thus relieving the urinary conditions associated with benign prostatic hypertrophy.

Indications of Prazosin

Benign prostatic hyperplasia
Anxiety and stress
High blood pressure
Heart failure
Post-traumatic stress disorder
High blood pressure (Hypertension)
Raynaud’s phenomenon
To improve urinary flow and symptoms of benign prostatic hyperplasia
Nightmares, sleep disturbance
Treatment of peripheral vasospasm
Management of hypertension associated with pheochromocytoma.
For the treatment of hypertension, symptomatic benign prostatic hyperplasia, and severe congestive heart failure. May also be used alone or in combination with β-blockers in the preoperative management of signs and symptoms of pheochromocytoma.

Dosage of Prazosin

Strengths: 1 mg; 2 mg; 5 mg

Hypertension

Initial dose: 1 mg orally 2 or 3 times a day
Maintenance dose: 1 to 20 mg orally per day in divided doses

Side Effects of Prazosin

The most common

More common

Fast or irregular heartbeat
appetite loss
changes in nails
constipation
fatigue
fever
Back pain
dizziness
a headache
increased cough
Acid or sour stomach
decreased appetite
Agitation
chest congestion
chest pain
cold sweats
confusion
decreased sexual ability or desire
stomach or abdominal cramps, gas, or pain
trouble sleeping

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Less common

bleeding gums
blood in the urine or stools
chest pain
diarrhea
Burning, crawling, itching, numbness, prickling, “pins and needles“, or tingling feelings
difficulty in moving
muscle stiffness
redness of the face, neck, arms and occasionally, upper chest
lack or loss of strength
muscle spasm
difficult or labored breathing
dry mouth
headache
irritability
lack or loss of strength
loose stools
loss of interest or pleasure
muscle stiffness
night sweats
passing gas
stomach discomfort, upset, or pain
swollen joints
trouble concentrating
increased blood pressure

Drug Interactions of Prazosin

Prazosin may interact with following drugs, supplements & may change the efficacy of drugs

dabigatran
diuretics (e.g., furosemide, hydrochlorothiazide)
linagliptin
other alpha 1 blockers (e.g., doxazosin, tamsulosin, terazosin)
other medications that reduce blood pressure (e.g., beta-blockers such as metoprolol and propranolol)
rituximab
sildenafil
tadalafil
vardenafil

Pregnancy & Lactation of Prazosin

FDA Pregnancy Category C

Pregnancy

This medication should not be used during pregnancy unless the benefits outweigh the risks. If you become pregnant while taking this medication, contact your doctor immediately.

Lactation

This medication passes into breast milk. If you are a breastfeeding mother and are taking prazosin, it may affect your baby. Talk to your doctor about whether you should continue breastfeeding. The safety and effectiveness of using this medication have not been established for children under 12 years of age.

References