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## Prazosin
### Overview
Prazosin is a selective alpha-1 adrenergic receptor antagonist.
### Primary Indications
* Hypertension
* Symptomatic Benign Prostatic Hyperplasia (BPH)
* Off-label: Raynaud's phenomenon, nightmares associated with PTSD
### Adult Dosing
* **Hypertension:** Initiate at 1 mg orally twice daily. Titrate slowly based on blood pressure response, usually every 4-6 weeks. Typical maintenance doses range from 3 mg to 20 mg per day divided into two doses. Maximum recommended daily dose is 20 mg, though some sources suggest up to 40 mg per day may be used in select cases under close monitoring.
* **BPH:** Initiate at 1 mg orally twice daily. Titrate to 2 mg orally twice daily, then to 5 mg orally twice daily as needed for symptomatic relief. Maximum dose is 5 mg twice daily.
* **PTSD Nightmares:** Initiate at 1 mg orally at bedtime. Doses may be increased by 1-2 mg per day. Typical effective doses range from 3 mg to 10 mg per day at bedtime. Maximum dose is typically 10 mg per day, but higher doses (up to 16 mg) have been reported in literature.
### Pediatric Dosing
Dosing in children is not well established and should be approached with caution and at the discretion of a specialist. Limited data suggests starting doses of 5-10 mcg/kg/dose orally twice daily, with increases as tolerated up to 25-50 mcg/kg/day divided into two doses. Maximum pediatric dose not well defined.
### Dose Adjustments
* **Renal Impairment:** Use with caution. No specific dose adjustment guidelines are universally established, but consider initiating at the lower end of the dosing range and titrating more slowly.
* **Hepatic Impairment:** Use with caution.
### Contraindications
* Hypersensitivity to prazosin or other quinazoline derivatives.
### Adverse Effects
Most common: Dizziness, drowsiness, headache, weakness, orthostatic hypotension (especially with the first dose or dose increases, often referred to as "first-dose phenomenon"), palpitations. Less common: Nausea, vomiting, blurred vision, dry mouth.
### Key Drug Interactions
* **Other Antihypertensives (e.g., diuretics, beta-blockers, calcium channel blockers):** Additive hypotensive effects.
* **Vasodilators (e.g., nitrates):** Potential for profound hypotension.
* **PDE5 inhibitors (e.g., sildenafil, tadalafil):** Increased risk of symptomatic hypotension. Avoid concurrent use or use with caution and at reduced doses.
### Monitoring
* Blood pressure (including orthostatic vital signs) at baseline and during dose titration.
* Symptoms of dizziness or syncope.
* Renal and hepatic function, especially in patients with pre-existing impairment.
### Clinical Pearls
* Administer the first dose at bedtime or with the patient in a supine position to minimize the risk of orthostatic hypotension.
* Advise patients to rise slowly from a sitting or lying position.
* Dosing for hypertension is typically divided twice daily, while for BPH it is also twice daily. PTSD nightmare dosing is usually at bedtime.
* Abrupt discontinuation can lead to rebound hypertension.
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*This information is intended for clinical use and does not replace a thorough review of the full prescribing information or consultation with other healthcare professionals. Always verify current prescribing information for any medication prior to use.*
