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# Prazosin
## Overview
Prazosin is an alpha-1 adrenergic blocker used primarily for hypertension and symptoms of benign prostatic hyperplasia (BPH).
## Primary Indications
* Hypertension
* Symptomatic Benign Prostatic Hyperplasia (BPH)
* Off-label: PTSD-related nightmares
## Adult Dosing
* **Hypertension:** Initiate at 1 mg orally twice daily. Titrate slowly upward based on blood pressure response, usually every 4 to 7 days. Typical maintenance dose: 1 mg to 5 mg orally twice daily. Maximum recommended dose: 20 mg orally daily in divided doses.
* **BPH:** Initiate at 1 mg orally twice daily. Titrate upward as needed and tolerated, typically to a maintenance dose of 1 mg to 5 mg orally twice daily. Maximum recommended dose: 20 mg orally daily in divided doses.
* **PTSD-related nightmares:** Initiate at 1 mg orally at bedtime. May titrate upwards by 1 mg to 2 mg increments weekly or as tolerated. Typical doses range from 2 mg to 10 mg orally at bedtime, though higher doses have been used.
## Pediatric Dosing
Dosing in pediatric patients is not well-established and should be guided by specialist recommendations and careful monitoring. One source suggests initiating at 12.5 mcg/kg/dose every 6 to 12 hours, with a maximum of 0.5 mg/kg/day or 10 mg/day, whichever is less.
## Dose Adjustments
* **Renal Impairment:** No specific dose adjustment is recommended by the manufacturer. However, caution and slower titration may be warranted in patients with significant renal impairment.
* **Hepatic Impairment:** No specific dose adjustment is recommended by the manufacturer. However, caution and slower titration may be warranted.
## Contraindications
* Known hypersensitivity to prazosin or other quinazoline derivatives.
## Adverse Effects
The most common adverse effects are orthostatic hypotension, dizziness, lightheadedness, headache, drowsiness, weakness, nausea, and palpitations. First-dose syncope is a significant concern, especially at the initiation of therapy or with dose increases. Other potential effects include blurred vision, dry mouth, edema, and rash.
## Key Drug Interactions
* **Other Antihypertensives:** Additive hypotensive effects may occur. Monitor blood pressure closely.
* **Diuretics:** Additive hypotensive effects.
* **Vasodilators (e.g., beta-blockers, nitrates):** May potentiate hypotensive effects.
* **Phosphodiesterase-5 (PDE5) inhibitors (e.g., sildenafil, tadalafil, vardenafil):** Use with caution; can cause additive hypotensive effects. Advise patients to avoid PDE5 inhibitors for at least 4 hours after taking prazosin.
## Monitoring
* Blood pressure (supine and standing) at baseline and regularly during therapy, especially after dose changes.
* Signs and symptoms of orthostatic hypotension (dizziness, lightheadedness, syncope).
* Renal and hepatic function periodically.
## Clinical Pearls
* Administer the first dose at bedtime to minimize the risk of syncope and orthostatic hypotension.
* Instruct patients to rise slowly from a sitting or lying position.
* Avoid dehydration and alcohol, as these can exacerbate hypotension.
* If a dose is missed, skip the missed dose and resume the regular dosing schedule. Do not double the dose.
* When switching from another antihypertensive, prazosin may be added gradually, and the dose of the other agent reduced as needed.
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*Disclaimer: This information is intended for clinical use and does not replace comprehensive prescribing information. Always consult the most current official drug labeling and relevant clinical guidelines before making treatment decisions.*
