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# Prazosin
## Overview
Prazosin is an alpha-1 adrenergic antagonist used primarily for hypertension and, off-label, for symptoms of post-traumatic stress disorder (PTSD) such as nightmares.
## Primary Indications
* Hypertension
* Symptomatic treatment of nightmares associated with PTSD (off-label)
## Adult Dosing
### Hypertension
* **Starting dose:** 1 mg two to three times daily.
* **Titration:** Gradually increase dose based on patient response, not to exceed a maximum of 20 mg/day (though some sources may suggest up to 40 mg/day in specific cases). Doses are typically divided every 8-12 hours.
* **Maintenance:** 1 mg to 10 mg two to three times daily.
### PTSD Nightmares
* **Starting dose:** 1 mg at bedtime.
* **Titration:** Gradually increase dose as tolerated, typically in increments of 1 mg per week. Doses can be divided, with the larger portion at bedtime.
* **Maintenance:** Doses typically range from 3 mg to 10 mg at bedtime, but can be higher. Some protocols suggest up to 16 mg/day.
**Note:** Dosing for both indications should be individualized and titrated cautiously. Specific titration schedules may vary based on local protocols.
## Pediatric Dosing
Dosing for pediatric patients is not well-established and should be considered off-label. If used, it requires careful titration and close monitoring. Pediatric dosing protocols may vary significantly.
## Dose Adjustments
* **Renal Impairment:** No specific dose adjustment is typically recommended, but caution and close monitoring are advised, especially in severe impairment.
## Contraindications
* Known hypersensitivity to prazosin or other quinazoline derivatives.
## Adverse Effects
* **Common:** Dizziness, lightheadedness, drowsiness, headache, orthostatic hypotension (especially upon initiating therapy or increasing dose), blurred vision, nausea.
* **Serious:** Syncope (fainting), priapism (prolonged erection), allergic reactions.
## Key Drug Interactions
* **Other antihypertensives:** Additive hypotensive effects.
* **Diuretics:** Increased risk of syncope.
* **Beta-blockers:** May worsen orthostatic hypotension.
* **Phosphodiesterase-5 (PDE5) inhibitors (e.g., sildenafil):** Significant additive hypotensive effects and increased risk of syncope. Concomitant use should be approached with extreme caution, and prazosin should be initiated at the lowest possible dose.
## Monitoring
* **Blood pressure:** Regularly, especially during initiation and titration, and particularly orthostatic vital signs (lying/sitting vs. standing).
* **Signs/symptoms of syncope or dizziness:** Advise patients to rise slowly from sitting or lying positions.
* **Signs/symptoms of priapism:** Advise patients to seek immediate medical attention if an erection lasts longer than 4 hours.
* **Kidney function:** In patients with renal impairment.
## Clinical Pearls
* The "first-dose phenomenon" can cause significant orthostatic hypotension and syncope, particularly with the initial dose. Advise patients to take the first dose at bedtime and avoid driving or operating machinery until they know how the medication affects them.
* For hypertension, prazosin is often used as an add-on therapy due to its rapid onset of action and potential for reflex tachycardia.
* For PTSD nightmares, it is generally taken at bedtime. Its effectiveness may be related to its effects on adrenergic tone during REM sleep.
* Discontinuation should be gradual to avoid rebound hypertension.
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*Disclaimer: This information is intended for healthcare professionals and is not a substitute for professional medical advice. Always consult the most current prescribing information and your local institutional protocols before making any decisions regarding patient care.*
