This medication's "-osin" suffix indicates its action as an alpha-adrenergic blocker.
Prazosin selectively blocks certain alpha1-adrenergic receptors causing blood vessel dilation and smooth muscle relaxation of the bladder neck and prostatic capsule. This action relaxes the blood vessels and allows blood to flow more easily.
As an alpha-1-adrenergic antagonist, prazosin is indicated to treat hypertension by decreasing blood pressure. This drug blocks the alpha receptors in the walls of blood vessels, allowing the vessels to relax and widen while decreasing peripheral vascular resistance.
Prostate gland enlargement is common in older men and causes urinary issues. Prazosin functions by blocking alpha receptors and relaxing the muscles surrounding the bladder neck (trigone and sphincter) and prostate capsule. This action allows urine to flow more easily in patients with BPH.
Prazosin is routinely given at a low dose for patients experiencing nightmares or sleep disturbances and is thought to do so by decreasing amounts of systemic adrenaline while sleeping.
Prazosin's blockade of adrenergic receptors affects the body's ability to vasoconstrict and maintain blood pressure. This medication may cause orthostatic hypotension. Instruct the patient to move slowly from a supine position to an upright position. Inform the patient to sit or lie down if experiencing dizziness or lightheadedness.
By causing the adrenergic receptors to widen blood vessels, Prazosin decreases vascular resistance and lowers the heart's effort to effectively pump blood throughout the body. The decrease in blood pressure triggers the body to overcompensate by increasing the heart rate.
Prazosin blocks adrenergic receptors in the prostate, causing relaxed blood vessels and increased blood flow. This blood flow can cause a painful, lasting erection - a condition known as priapism.
Prazosin affects the adrenergic receptors in the nasal mucosa and causes vasodilation of the nasal arterioles. Inform the patient that this drug may cause nasal congestion.
Profound orthostatic hypotension may occur with initial prazosin administration. A small percentage of patients may lose consciousness within 60 minutes of taking the medication. To minimize the first dose effect, the initial dose should be 1 mg or less and administered at bedtime.
Since this medication blocks alpha-1-adrenergic receptors and affects the body's ability to vasoconstrict, administer prazosin at bedtime to minimize the high risk of orthostatic hypotension and syncope.
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