oral administration and maximal effects seen within
2–4 hours. Although it is most commonly adminis-
tered in a loading regimen of 0.1–0.2 mg followed by
0.1 mg hourly for several hours, evidence suggests that
comparable responses may be seen with a single 0.2
mg dose.3 The most common adverse effect seen in
the acute setting is drowsiness, affecting up to 45% of
patients. Clonidine may be a poor choice when moni-
toring of mental status is important. Dry mouth is also
a common complaint and lightheadedness is occasion-
ally observed.
Labetalol is a combined α- and β-adrenergic
blocking agent. It can be effective given orally in a
dose of 200–400 mg, which may be repeated after
2–3 hours. The onset of effect is observed within 1–2
hours.9,10 Like any β blocking agent, it has the po-
tential to induce heart block and to worsen symp-
toms of bronchospasm. Therefore, it should be
avoided in patients with uncontrolled asthma or
those with more than first-degree heart block, symp-
tomatic bradycardia, or congestive heart failure.
Prazosin is an α-adrenergic blocking agent that
can have limited benefit in the early management of
pheochromocytoma. Side effects include first-dose
syncope, palpitations, tachycardia, and orthostatic
hypertension.
AGENTS FOR HYPERTENSIVE
EMERGENCIES
Parenteral Agents
The following parenteral agents are effective in treat-
ing hypertensive emergencies (see Table IV).7 La-
betalol has proved particularly effective when used in
bolus intravenous injections in the initial treatment
of hypertensive emergencies, and can provide a con-
trolled reduction in blood pressure to a predeter-
mined goal.11 Once a goal pressure is achieved,
injections are stopped, and the long duration of
action facilitates conversion to effective oral therapy.