Prazosin is the first highly selective α1 blocker. It blocks sympathetically mediated vasoconstriction and produces a fall in BP, which is attended by only mild tachycardia. Norepinephrine release is not increased due to the absence of α2 blockade.
Mechanism of action.
It is an alpha-1 blocker.
- Inhibits postsynaptic alpha-adrenergic receptors, causing arterial and venous dilation and a subsequent decrease in blood pressure.
- It also inhibits phosphodiesterase, which degrades cAMP.
Clinical uses.
- Hypertension.
- PTSD- related nightmares and sleep disruption.
- Benign prostate hypertrophy.
Adverse effects.
- Dizziness and fainting.
- Nausea and palpitations.
- Miosis
- Orthostatic hypotension.
- Nasal stuffiness
- Urinary incontinence.
- Inhibition of ejaculation.
Drug interaction.
- Prazosin and acebutolol both increase anti-hypertensive channel blocking, hence should be closely monitored.
- Yohimbe increases the effects of prazosin by pharmacodynamic synergism.
Contraindication.
- Hypersensitivity to the drug.
- Narcolepsy.
- Heart failure.
- Prostatic carcinoma.
Dosage.
- PRAZOPRES 0.5, 1.0 and 2.0 mg tablets. Start with 0.5–1 mg at bedtime; the usual dose is 1–4 mg BD or TDS.
- MINIPRESS XL: Prazosin GITS.
