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### Prazosin
#### Overview
Prazosin is an alpha-1 adrenergic blocker.
#### Primary Indications
* Hypertension (less commonly used now as first-line therapy)
* Symptomatic benign prostatic hyperplasia (BPH)
* Off-label: PTSD-related nightmares
#### Adult Dosing
* **Hypertension:** Start with 1 mg orally once or twice daily. Titrate slowly every 1-2 weeks based on response and tolerance. Usual maintenance dose: 3-15 mg per day in 2-3 divided doses. Maximum: 20 mg per day.
* **BPH:** Start with 1 mg orally once or twice daily. Titrate slowly based on response and tolerance. Usual maintenance dose: 1-5 mg per day in 2-3 divided doses. Maximum: 10 mg per day.
* **PTSD Nightmares:** Start with 1 mg orally at bedtime. Titrate slowly based on efficacy and tolerance, typically increasing by 1 mg per week. Usual dose: 2-6 mg at bedtime. Maximum: 10 mg at bedtime.
#### Pediatric Dosing
* Prazosin is generally not recommended for pediatric patients due to lack of established efficacy and safety data.
#### Dose Adjustments
* **Renal Impairment:** No specific dose adjustment is typically recommended, but monitor for increased adverse effects due to potential accumulation.
* **Hepatic Impairment:** Use with caution; no specific guidelines, but reduced metabolism may necessitate lower doses and slower titration.
#### Contraindications
* Known hypersensitivity to prazosin or other quinazoline derivatives.
#### Adverse Effects
* **Common:** Dizziness, lightheadedness, headache, drowsiness, weakness, nausea.
* **Serious:** Hypotension (especially orthostatic hypotension and syncope, particularly with the first dose or dose increases), palpitations, priapism.
#### Key Drug Interactions
* **Other Antihypertensives:** Additive hypotensive effects.
* **Diuretics:** Increased risk of hypotension.
* **Beta-blockers:** May increase the risk of profound orthostatic hypotension when initiated concurrently.
* **PDE-5 Inhibitors (e.g., sildenafil):** Increased risk of symptomatic hypotension.
#### Monitoring
* Blood pressure, particularly orthostatic vital signs, especially after initiating therapy and with dose increases.
* Signs and symptoms of fluid retention.
* For BPH indication: urinary symptoms.
#### Clinical Pearls
* The "first-dose phenomenon" (marked hypotension and syncope) can occur with the initial dose, dose increase, or when restarting therapy after a break. Advise patients to take the first dose at bedtime and avoid driving or hazardous activities until they know how the medication affects them.
* Caution is advised when changing positions (e.g., standing up from a sitting or lying position).
* Prazosin may cause a positive result on immunoassay screening for certain drugs (e.g., tricyclic antidepressants).
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*Please verify current prescribing information with the official product monograph or other reliable resources.*
