Phentolamine adverse effects

Phentolamine is a potent competitive antagonist at both K and k2 receptors (Table 10-1). Phentolamine reduces peripheral resistance through blockade of K receptors and possibly k2 receptors on vascular smooth muscle. Its cardiac stimulation is due to antagonism of presynaptic k2 receptors (leading to enhanced release of norepinephrine from sympathetic nerves) and sympathetic activation from baroreflex mechanisms. Phentolamine also has minor inhibitory effects at serotonin receptors and agonist effects at muscarinic and Hi and H2 histamine receptors. Phentolamine s principal adverse effects are related to cardiac stimulation, which may cause severe tachycardia, arrhythmias, and myocardial ischemia. Phentolamine has been used in the treatment of pheochromocytoma. Unfortunately oral and intravenous formulations of phentolamine are no longer consistently available in the United States. 

The correct answer = A. Doxazosin is an competitive blocker at the oci receptor and lowers blood pressure. In addition it blocks the smooth muscle of the bladder neck and prostate to improve urine flow. Labetalol and propranolol, while effective for treating the hypertension, are contraindicated in an asthmatic. They would not improve urine flow. Phentolamine has too many adverse effects to be used as an hyper-I tensive agent. Isoproterenol is a p agonist and is not employed as an hypertensive nor would it affect urinary function. 

Phentolamine is a non-selective alpha-adrenoceptor antagonist. It is used to treat hypertensive crises attributable to the effects of noradrenahne, as in pheochromo-cytoma and during the interaction of monoamine oxidase inhibitors with amine-containing medicaments and foods (1). Its adverse effects are similar to those of phenoxy-benzamine. 

Papaverine is not FDA approved for erectile dysfunction. Intracavernosal papaverine alone is not commonly used for management of erectile dysfunction because large doses are required, and these produce dose-related adverse effects priapism, corporal fibrosis, hypotension, and hepatotoxicity. Papaverine is more often administered in lower doses combined with phentolamine and/or alprostadil. A variety of formulae have been used, but no one mixture has been proven better than other mixtures (see Table 81-6). Combination formulations are considered to be safer and associated with the potential for fewer serious adverse effects than high doses of any one of these agents. ... 

Phentolamine has most often been administered as an intracavernosal injection. Monotherapy is avoided, as large doses are required for an erection, and at these doses systemic hypotensive adverse effects would be prevalent. Most often, phentolamine has been used in combination with other vasoactive agents for intracavernosal administration. A ratio of 30 mg papaverine to 0.5 to 1 mg phentolamine is typical, and the usual dose ranges from 0.1 mL to 1 mL of the mixture. Such a mixture promotes local effects of phentolamine and minimizes systemic hypotensive adverse effects (see Table 81-6). ... 

Hypotension is the most common adverse effect of intracavernosal phentolamine. It is more common and more severe with large doses or in patients with poor injection technique who have injected into a vein (rather than the cavernosa). Prolonged erections have also been reported in patients who used excessive doses of combination intracavernosal therapy. 

The dose-dependent adverse effects of phentolamine include nausea, vomiting, diarrhea, nasal stuffiness, hypotension, tachycardia, dizziness, flushing, and weakness. 

Hypotension is the major adverse effect of phentolamine reflex carSac stimulation may cause tachycardia, arrhythmias, and ischemic carSac events. GI stimulation may result in abdominal pain, nausea, and exacerbation of peptic ulcer. Phentolamine should be used with particular caution in patients with coronary artery disease or a history of peptic ulcer. 

E. Adrenoceptor Blockers Alpha -selective agents (eg, prazosin) and beta-blockers (eg, propranolol) are effective antihypertensive drugs. Alpha-blockers reduce vascular resistance and venous return. The nonselective alpha-blockers (phentolamine, phenoxybenzamine) are of no value in chronic hypertension because of excessive compensatory responses, especially tachycardia. Alpha,-selective adrenoceptor blockers are relatively free of the severe adverse effects of the nonselective alpha-blockers and postganglionic nerve terminal sympathoplegic agents. 

Phentolamine [RegitineJ. Phentolamine is a competitive alpha antagonist used primarily to control blood pressure during management of pheochromocytoma. The drug is usually administered via intravenous or intramuscular injection. Phentolamine is not usually used to treat essential hypertension because with prolonged use, effectiveness tends to decrease and patients begin to develop adverse side effects. 

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