Why is terazosin (alpha-1 blocker) given prior to a procedure in an adult patient with hypertension and an adrenal adenoma secreting excess catecholamines?

Why Terazosin is Given Prior to Procedure in Adrenal Adenoma

Terazosin (an alpha-1 blocker) is administered preoperatively to prevent life-threatening hypertensive crises and arrhythmias caused by massive catecholamine release during surgical manipulation of catecholamine-secreting adrenal tumors (pheochromocytomas). 1

Critical Prerequisite: Confirm Catecholamine Secretion

Before understanding the rationale for alpha-blockade, you must first determine if the adrenal adenoma is actually secreting catecholamines:

• Not all adrenal adenomas require alpha-blockade — only those producing norepinephrine or epinephrine (pheochromocytomas) 1, 2
• Measure plasma or urine metanephrines preoperatively to identify catecholamine-secreting tumors 2
• Adenomas secreting only cortisol, aldosterone, or non-functional adenomas do not require alpha-blockade 1

Mechanism and Rationale for Alpha-Blockade

The fundamental problem: Surgical manipulation of catecholamine-secreting tumors causes massive release of norepinephrine and epinephrine into circulation, triggering potentially fatal hypertensive emergencies and cardiac arrhythmias 1

How terazosin prevents this:

• Terazosin is a selective alpha-1 adrenergic receptor antagonist that blocks peripheral vasoconstriction caused by catecholamines 3, 4
• By occupying alpha-1 receptors, it prevents the hypertensive response when catecholamines are released during tumor manipulation 1, 4
• This blockade must be established before surgery to prevent catastrophic hemodynamic instability 1

Specific Preoperative Protocol

Timing and duration:

• Alpha-blockade must be initiated at least 10-14 days before surgery 1, 2
• This duration allows adequate receptor blockade and volume expansion 1

Blood pressure targets during preoperative preparation:

• Supine BP: <130/80 mmHg 1
• Standing systolic BP: preferably >90 mmHg to avoid orthostatic hypotension 1

Terazosin dosing:

• While the ESMO guidelines specifically mention doxazosin as the preferred selective alpha-1 blocker, terazosin is pharmacologically equivalent and may be used as an alternative 1
• Terazosin has a longer half-life than prazosin (allowing once-daily dosing) and more predictable absorption, facilitating dose titration 3, 5
• The ESC guidelines explicitly list terazosin as an appropriate alpha-1 blocker for adrenergic crises in pheochromocytoma 1

Critical Sequencing: Never Beta-Block First

A potentially fatal error: Never administer beta-blockers before establishing alpha-blockade 1, 4

Why this is dangerous:

• Beta-blockade eliminates vasodilatory beta-2 receptors in peripheral vessels 4
• This leaves unopposed alpha-receptor stimulation, causing paradoxical severe hypertension 4
• Beta-blockers should only be added after adequate alpha-blockade if tachyarrhythmias develop 1

Additional Agents When Terazosin Alone is Insufficient

If target blood pressure is not achieved with alpha-blockade alone:

• Add calcium channel blockers (nifedipine slow-release) as second-line 1
• Consider metyrosine (inhibits catecholamine synthesis) where available 1
• Avoid short-acting sublingual nifedipine — potentially dangerous in hypertensive emergencies 4

Important Exception: Dopamine-Only Secreting Tumors

Do not give alpha-blockade for purely dopamine-secreting adenomas 1

• Dopamine-only tumors (identified by isolated elevation of plasma methoxytyramine) typically cause normotension or hypotension, not hypertension 1
• Alpha-blockade is unnecessary and potentially harmful in these cases 1
• These patients require monitoring for hypotension rather than hypertensive crisis 1

Intraoperative and Postoperative Considerations

During surgery:

• Despite preoperative alpha-blockade, intraoperative hypertension may still occur and should be treated with IV phentolamine, magnesium sulfate, calcium channel blockers, or nitroprusside 1, 6
• Tachycardia is managed with IV esmolol (beta-1 selective blocker) 1, 6

After tumor removal:

• Anticipate profound hypotension due to sudden catecholamine withdrawal and pre-existing peripheral hypovolemia 1, 7
• Aggressive fluid resuscitation with saline should begin the day before surgery to prevent postoperative hypotension 1, 7
• Monitor glucose closely as hypoglycemia commonly occurs after catecholamine levels drop 1, 7

Common Pitfalls to Avoid

• Never biopsy a suspected pheochromocytoma — this can precipitate fatal hypertensive crisis 2, 6
• Never start beta-blockers before alpha-blockade — causes unopposed alpha-stimulation and severe hypertension 1, 4
• Never use labetalol as monotherapy — despite having both alpha and beta properties, experimental evidence does not support its use in this setting 4
• Do not assume all adrenal adenomas need alpha-blockade — only catecholamine-secreting tumors require this preparation 1, 2