Phenoxybenzamine applications

Today, phenoxybenzamine is not used as a general antihypertensive, but rather, it finds application in prolonged pheochromocytoma therapy. If tachycardia occurs, a (i-blocker can be added to prevent it. In addition, it can be a useful drug in urinary retention cases due to paralytic bladder and other outlet obstructions (also see urecholine for the cholinergic approach to such problems, Chapter 8). Dibenzylene may also be of value in voiding disturbances due to prostatic obstruction. 

Phenoxybenzamine is not useful in essential hypertension because it causes severe tachycardia and marked orthostatic hypotension. The drug is used in Raynaud s phenomenon, but efficacy in this application is controversial. The answer is (B). 

It is a potent alpha-adrenoceptor (ai and 02) blocking agent with a prolonged duration of action. Phenoxybenzamine hydrochloride has been employed intravenously in the treatment of shock. It also finds its application in the treatment ofpulmonary oedema. 

The original a-antagonists did not distinguish between ai- and a2 types and found only a few therapeutic applications, but they gave some help in frostbite and other, more long-term, cases of impaired circulation. Typical examples were the imidazolines such as phentolamine (12.48) and the chlorethylamines such as phenoxybenzamine (12.49). The latter became activated by self-quaternization (defined on p. 577) and caused irreversible alkylation of ar receptors. 

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