indication

For the treatment of phaeochromocytoma (malignant), benign prostatic hypertrophy and malignant essential hypertension.

pharmacology

Phenoxybenzamine is indicated for the control of episodes of hypertension and sweating that occur with a disease called pheochromocytoma. If tachycardia is excessive, it may be necessary to use a beta-blocking agent concomitantly. Phenoxybenzamine is a long-acting, adrenergic, alpha-receptor blocking agent which can produce and maintain "chemical sympathectomy" by oral administration. It increases blood flow to the skin, mucosa and abdominal viscera, and lowers both supine and erect blood pressures. It has no effect on the parasympathetic system. Phenoxybenzamine works by blocking alpha receptors in certain parts of the body. Alpha receptors are present in the muscle that lines the walls of blood vessels. When the receptors are blocked by Phenoxybenzamine, the muscle relaxes and the blood vessels widen. This widening of the blood vessels results in a lowering of blood pressure.

mechanism of action

Phenoxybenzamine produces its therapeutic actions by blocking alpha receptors, leading to a muscle relaxation and a widening of the blood vessels. This widening of the blood vessels results in a lowering of blood pressure.

toxicity

Symptoms of overdose are largely the result of block of the sympathetic nervous system and of the circulating epinephrine. They may include postural hypotension resulting in dizziness or fainting, tachycardia, particularly postural, vomiting; lethargy, and shock.

absorption

Twenty to 30 percent of orally administered phenoxybenzamine appears to be absorbed in the active form.

half life

24 hours

drug interactions

Tadalafil: Tadalafil may enhance the hypotensive effect of Phenoxybenzamine. Monitor for hypotension during concomitant therapy.

Tamsulosin: Concomitant use of alpha1-adrenergic antagonists, Tamsulosin and Phenoxybenzamine, may result in additive antihypertensive effects. Combination therapy is not recommended.

Treprostinil: Additive hypotensive effect. Monitor antihypertensive therapy during concomitant use.

Vardenafil: Additive hypotensive effects of the PDE5 inhibitor, Vardenafil, and alpha1-blocker, Phenoxybenzamine, may occur. Monitor for hypotension during concomitant therapy.