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244 SEcTIoN II Pharmacology ` PHARMACOLOGY—AUTONOMIC dRUGS Pharmacology ` PHARMACOLOGY—AUTONOMIC dRUGS

α-blockers
dRUG APPLICATIONS AdVERSE EFFECTS
Nonselective
Phenoxybenzamine Irreversible. Pheochromocytoma (used
preoperatively) to prevent catecholamine
(hypertensive) crisis
Orthostatic hypotension, reflex tachycardia
Phentolamine Reversible. Given to patients on MAO inhibitors
who eat tyramine-containing foods and for
severe cocaine-induced hypertension (2nd line)
α 1 selective (-osin ending)
Prazosin, terazosin, Urinary symptoms of BPH; PTSD (prazosin); 1st-dose orthostatic hypotension, dizziness,
doxazosin, hypertension (except tamsulosin) headache
tamsulosin
α 2 selective
Mirtazapine Depression Sedation,  serum cholesterol,  appetite

Epinephrine Phenylephrine
Before α-blockade After α-blockade Before α-blockade After α-blockade

Net pressor
Net pressor
Blood pressure Net depressor Blood pressure α 1
eect
Systolic
2
MAP β > α 1 Unopposed β 2 Suppression of
Diastolic
β 1
β , reflex tachycardia
1
Heart rate Heart rate Reflex bradycardia

Time Time
Epinephrine response exhibits reversal of mean arterial Phenylephrine response is suppressed but not reversed
pressure from a net increase (the α response) to a net because it is a “pure” α-agonist (lacks β-agonist
decrease (the β 2 response). properties).

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