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# Prazosin
## Overview
Prazosin is a selective, competitive alpha-1 adrenergic antagonist. By blocking postsynaptic alpha-1 receptors, it causes vasodilation of both arterioles and veins, reducing peripheral vascular resistance. It is short-acting and possesses a high risk for orthostatic hypotension.
## Primary Indications
* Hypertension (off-label as primary, traditionally used as add-on).
* Benign Prostatic Hyperplasia (BPH).
* PTSD-associated nightmares and sleep disturbances (off-label).
* Raynaud’s phenomenon (off-label).
## Adult Dosing
* **Hypertension:** Start 1 mg at bedtime to minimize "first-dose" syncope. Titrate slowly based on response. Maintenance: 6 mg to 15 mg daily in 2–3 divided doses. Maximum: 20 mg/day.
* **PTSD-associated Nightmares:** Start 1 mg at bedtime. Titrate every 3–7 days. Typical effective range: 2 mg to 10 mg at bedtime.
* **BPH:** Initial: 1 mg twice daily. Maintenance: 2 mg twice daily.
## Pediatric Dosing
* **Hypertension (Off-label):** Initial: 0.05 mg/kg/dose every 6–8 hours.
* **Titration:** Increase as needed; max 0.4 mg/kg/day or 20 mg/day (whichever is lower).
* *Note: Dosing depends on institutional protocol; clinical context (emergency vs. chronic) significantly impacts approach.*
## Dose Adjustments
* **Renal/Hepatic Impairment:** No formal standardized dosing adjustments exist, but use with extreme caution. Start at the lowest possible dose (0.5–1 mg) and titrate very slowly, as metabolism may be altered and sensitivity to hypotensive effects may be increased.
## Contraindications
* Known hypersensitivity to prazosin or other quinazolines (e.g., terazosin, doxazosin).
## Adverse Effects
* **Common:** Dizziness, headache, drowsiness, nausea, palpitations.
* **Serious:** Orthostatic hypotension (highest risk with first dose), syncope, reflex tachycardia, priapism (rare but significant).
## Key Drug Interactions
* **PDE-5 Inhibitors (e.g., Sildenafil, Tadalafil):** Synergistic effects can cause severe, symptomatic hypotension.
* **Other Antihypertensives:** Increased risk of additive hypotensive effects.
* **Beta-Blockers:** May exacerbate first-dose hypotensive reactions.
## Monitoring
* Blood pressure (specifically orthostatic vitals during initiation/titration).
* Heart rate.
* Symptoms of dizziness or syncope.
* Bladder/prostate symptoms (if used for BPH).
## Clinical Pearls
* **First-Dose Phenomenon:** Instruct patients to take the first dose at bedtime while lying down. Advise rising slowly from a seated or supine position to avoid falls.
* **Tolerance:** Tolerance to the hypotensive effect may develop over time.
* **Off-label Use:** For PTSD, efficacy is based on the suppression of REM-associated sympathetic surges; it does not treat the underlying trauma.
* **Surgical Warning:** Note if a patient is taking alpha-blockers prior to cataract surgery, as it is associated with "Intraoperative Floppy Iris Syndrome" (IFIS).
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**Educational Disclaimer:** This information is for educational purposes only. Always verify dosages, contraindications, and drug interactions against current institutional protocols, primary literature (e.g., Lexicomp, UpToDate), and the official FDA-approved product labeling before prescribing or administering medication.
