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# Prazosin
## Overview
Prazosin is an alpha-1 adrenergic blocker used to treat hypertension and symptoms of benign prostatic hyperplasia (BPH). It causes vasodilation by blocking postsynaptic alpha-1 adrenergic receptors.
## Primary Indications
* Hypertension
* Symptomatic Benign Prostatic Hyperplasia (BPH)
* Off-label: PTSD-related nightmares (though this is an off-label use, it's a common consideration for prazosin)
## Adult Dosing
* **Hypertension:** Initiate at 1 mg orally two to three times daily. Titrate slowly upwards based on blood pressure response, typically every 4-6 weeks. Usual maintenance dose: 3-20 mg per day in divided doses. Maximum daily dose: 20 mg.
* **BPH:** Initiate at 1 mg orally two to three times daily. Titrate upwards as needed. Usual maintenance dose: 2-10 mg per day in divided doses. Maximum daily dose: 20 mg.
* **PTSD-related nightmares (off-label):** Dosing varies, but often initiated at 1-2 mg at bedtime. Doses up to 10 mg at bedtime have been reported.
## Pediatric Dosing
There is limited pediatric data for prazosin. Dosing is not well-established and should be individualized by a clinician experienced in pediatric pharmacology.
## Dose Adjustments
* **Renal Impairment:** No specific dose adjustment is routinely recommended, but caution and careful monitoring are advised.
* **Hepatic Impairment:** No specific dose adjustment is routinely recommended, but caution is advised.
## Contraindications
* Hypersensitivity to prazosin or other quinazolines.
## Adverse Effects
* **Common:** Dizziness, lightheadedness, drowsiness, headache, weakness, nausea.
* **Serious:** Orthostatic hypotension (especially with the first dose or dose increases), syncope, palpitations, priapism (rare).
## Key Drug Interactions
* **Other antihypertensives (e.g., diuretics, beta-blockers, calcium channel blockers):** Additive hypotensive effects.
* **Beta-blockers:** May increase the risk of severe orthostatic hypotension, especially at the start of therapy.
* **Vasodilators (e.g., nitrates):** Increased risk of hypotension.
* **Phosphodiesterase-5 (PDE5) inhibitors (e.g., sildenafil, tadalafil):** Significant additive hypotensive effects. Concomitant use is generally not recommended or requires extreme caution and dose adjustments.
## Monitoring
* Blood pressure, especially orthostatic vital signs, particularly after initiation and with dose changes.
* Symptoms of dizziness or syncope.
* Renal and hepatic function as clinically indicated.
## Clinical Pearls
* **First-dose phenomenon:** Patients may experience significant orthostatic hypotension, dizziness, or syncope with the first dose or with rapid increases in dose. Advise patients to take the first dose at bedtime and to avoid activities requiring mental alertness until they know how the medication affects them.
* Administer doses consistently with respect to food and time of day.
* Inform patients about the potential for dizziness and to rise slowly from a sitting or lying position.
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*Disclaimer: This information is intended for clinical professionals and is not a substitute for professional medical advice. Always verify current prescribing information with the official drug labeling or a trusted drug information resource.*
