Drug for management of hypeension in Phaeochromocytoma
Correct Answer: Phenoxybenzamine
Description: Ans. is 'a' i.e., Phenoxybenzamine Once a pheochromocytoma is diagnosed, all patients should undergo a resection of the pheochromocytoma following appropriate medical preparation. Resetting a pheochromocytoma is a high-risk surgical procedure and an experienced surgeon/anesthesiologist team is required. Some form of preoperative pharmacologic preparation is indicated for all patients with catecholamine-secreting neoplasms. Preoperative medical therapy is aimed at: Controlling hypeension (including preventing a hypeensive crisis during surgery) o Volume expansion In patients with undiagnosed pheochromocytomas who undergo surgery for other reasons (and who therefore have not undergone preoperative medical therapy), surgical moality rates are high due to lethal hypeensive crises, malignant arrhythmias, and multiorgan failure. Combined alpha- and beta-adrenergic blockade Combined alpha- and beta-adrenergic blockade is the most common approach to control blood pressure and prevent intraoperative hypeensive crises. Alpha-adrenergic blockade An alpha-adrenergic blocker is given 10 to 14 days preoperatively to normalize blood pressure and expand the contracted blood volume. Phenoxybenzamine is the preferred drug for preoperative preparation to control blood pressure and arrhythmia in most centers in the United States. It is an irreversible, long-acting, nonspecific alpha-adrenergic blocking agent. The initial dose is 10 mg once or twice daily, and the dose is increased by 10 to 20 mg in divided doses every two to three days as needed to control blood pressure and spells. The final dose of phenoxybenzamine is typically between 20 and 100 mg daily. Beta-adrenergic blockade After adequate alpha-adrenergic blockade has been achieved, beta-adrenergic blockade is initiated, which typically occurs two to three days preoperatively. The beta-adrenergic blocker should never be staed first because blockade of vasodilatory peripheral betaadrenergic receptors with unopposed alpha-adrenergic receptor stimulation can lead to a fuher elevation in blood pressure. The alternatives to a and 13 adrenergic agents are calcium channel blockers and metyrosine. Calcium channel blockers Although perioperative alpha-adrenergic blockade is widely recommended, a second regimen that has been utilized involves the administration of a calcium channel blocker. Nicardipine is the most commonly used calcium channel blocker in this setting; the staing dose is 30 mg twice daily of the sustained release preparation. Metyrosine Another approach involves the administration of metyrosine (alpha-methyl Para-tyrosine), which inhibits catecholamine synthesis.
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