A 40 yrs old man was diagnosed to have a pheochromocytoma tumor. Staging investigations showed the tumour to be operable. What definite therapy will the patient most likely be started on a few weeks before the surgery:
a) verapamil
b) sodium nitroprusside
c) phenoxybenzamine
d) nitroglycerine
e) none of the above
Answer:
c) phenoxybenzamine
Explanation
Pheochromocytoma is a tumor of the adrenal medulla.The adrenal medulla is responsible for the secretion of catecholamines(epinephrine & norepinephrine) in the body. due to the tumor, excess levels of catecholamines(CAs) are seen in the body. The main effect of the high levels of circulating catecholamines is episodes of hypertension due to peripheral vasoconstriction. The patient can have sudden episodes of very high blood pressure which can result in stroke, myocardial infarction, left ventricular failure etc.The treatment of choice for the tumor is surgical removal of the tumor. Phenoxybenzamine is the drug commonly used to prepare the patient for a pheochromocytoma surgery (startde 6wks in advance). Phenoxybenzamine belong to the class of beta-haloalkylamines and is a non selective alpha adrenoreceptor blocker. It cyclizes spontaneously in the body giving rise to a highly reactive ethylenminium intermediate which binds with alpha adrenoreceptors for a period of 3-4 days.Phenoxybenzamine is used to prepare a phechromocytoma patient for surgery because i) due to excess to excess circulating CAs there is peripheral vasoconstriction which causes the high BP. treatment with an alpha blocker produces peripheral vasodilatation and pooling of blood resulting in a decrease in BP. ii) handling of tumor during surgery causes marked outpouring of of CAs in blood causing sudden intra-operative rise in BP. this can be prevented if phenoxybenzamine has been given earlier. Verapamil though a commonly used anti hypertensive drug is not used as it is a calcium channel blocker and would not decrease the BP due to catecholamine excess. Sodium nitroprusside is a drug used in hypertensive emergency and is not useful to control the BP for a prolonged period before the surgery. It is also not very useful intraoperatively. Nitroglycerine is an anti-angina drug and not useful in controlling hypertension.