A report on Beta blocker, Norepinephrine, Phentolamine and Pheochromocytoma

Beta blockers are competitive antagonists that block the receptor sites for the endogenous catecholamines epinephrine (adrenaline) and norepinephrine (noradrenaline) on adrenergic beta receptors, of the sympathetic nervous system, which mediates the fight-or-flight response.

This hypotension is sensed by the baroreceptor reflex, which results in increased sympathetic nerve firing on the heart, releasing norepinephrine.

The primary application for phentolamine is for the control of hypertensive emergencies, most notably due to pheochromocytoma.

It also has usefulness in the treatment of cocaine-induced cardiovascular complications, where one would generally avoid β-blockers (e.g. metoprolol), as they can cause unopposed α-adrenergic mediated coronary vasoconstriction, worsening myocardial ischemia and hypertension.

Beta blockers, which counter some of the effects of noradrenaline by blocking their receptors, are frequently used to treat glaucoma, migraine, and a range of cardiovascular problems.

Phaeochromocytoma, in conjunction with α-blocker

3) Toxic Myocarditis: Even in patients without myocardial damage, excessive catecholamines can result in abnormal ST changes on an ECG. Norepinephrine (a catecholamine) is hypothesized to result in damaged cardiac tissue by inhibiting coronary blood flow and depriving cells of oxygen, thus resulting in ischemic tissue. Fortunately, following tumor excision and the subsequent quelling of catecholamines, the damage has been proven reversible.

2) Pharmaceutical Interference: Many prescription, over-the-counter, and illicit substances can interfere with the proper collection of plasma metanephrines and lead to false-positive results. Providers should review a patient's medication list in-detail and have a discussion if temporarily discontinuing any of the interfering medications is possible. The most reported medications to result in falsely elevated metanephrines include: β-adrenoceptor blockers, phenoxybenzamine, tricyclic antidepressants, monoamine oxidase inhibitors, serotonin norepinephrine reuptake inhibitors (SNRI), and methyldopa. As the majority of these medications are commonly prescribed for psychiatric conditions, a conversation with the prescriber may be necessary to facilitate alternative therapeutic options while the patient is undergoing evaluation for a pheochromocytoma. After any possible prescription medications have been held, it is important to review any over-the-counter medications/supplements as well as the commonly used acetaminophen and pseudoephedrine cause false elevations in metanephrine levels. Finally, it is important to have open, non-judgemental discussions about the patient's recreational substance use. Amphetamines, nicotine, and cocaine can result in marked plasma norepinephrine levels.

Other appropriate antihypertensive drugs to administer during hypertensive crisis resulting from stimulant overdose are vasodilators such as nitroglycerin, diuretics such as furosemide, and alpha blockers such as phentolamine.

Drugs such as phentolamine that act on both types of receptors can produce a complex combination of both effects.

A pheochromocytoma is a rarely occurring tumor of the adrenal medulla, caused either by genetic factors or certain types of cancer.

1) Hypertension: In the pheochromocytoma patient, postoperative hypertension could indicate incomplete tumor resection or another tumor of unknown location. However, the traditional, non-specific causes of postoperative hypertension including pain, fluid overload, and essential hypertension must also be considered. A perioperative hypertensive crisis is first treated with a 5.0 milligram (mg) intravenous bolus of phentolamine, with additional 5.0 mg dose every ten minutes until the blood pressure falls within an acceptable range. If the blood pressure is only minimally elevated, the patient can resume their alpha and beta-adrenoceptor antagonist from prior to surgery.