Drugs Commonly Used In the Treatment of Hypertensive Emergencies

6. Labetalol hydrochloride

Labetalol is a non-cardioselective beta-blocker with intrinsic sympathomimetic activity/ alpha-1 blocker used in the treatment of hypertensive emergencies, including severe hypertension of pregnancy, when rapid control of blood pressure is essential. It is also used in hypertensive episodes following acute myocardial infarction and in anaesthesia when a hypotensive technique is indicated.

Labetalol acts by blocking alpha- and beta-adrenergic receptors, resulting in decreased peripheral vascular resistance without significant alteration of heart rate or cardiac output.

Dose/ Route: 2 mg/minute IV or 20 – 80 mg every 10 minutes up to 300 mg total dose
Onset of action: 5 – 10 minutes
Duration of action: 3 – 6 hours

Contraindications

Labetalol is contraindicated in

• Acute decompensated heart failure because of its β-blocking properties
• Asthma or obstructive airway disease,
• Severe bradycardia, 2°/3° heart block (without pacemaker)
• Cardiogenic shock
• Bronchial asthma
• Uncompensated cardiac failure
• Hypersensitivity to labetalol
• Sinus bradycardia
• Sick sinus syndrome without permanent pacemaker
• Conditions associated with prolonged and severe hypotension

Adverse effects

• Vomiting,
• Scalp tingling,
• Bronchoconstriction
• Dizziness
• Nausea
• Heart block
• Orthostatic hypotension

7. Nicardipine hydrochloride

Nicardipine is a dihydropyridine calcium-​channel blocker indicated for short-term treatment of hypertension when the oral route is not feasible or desirable, particularly in the event of:

• Malignant arterial hypertension/Hypertensive encephalopathy
• Aortic dissection, when short-acting beta-blocker therapy is not suitable, or in combination with a beta-blocker when beta-blockade alone is not effective
• Severe pre-eclampsia, when other intravenous antihypertensive agents are not recommended or are contraindicated
• Treatment of postoperative hypertension

Just like Clevidipine, Nicardipine acts by inhibiting transmembrane influx of extracellular calcium ions across membranes of myocardial cells and vascular smooth muscle cells, without changing serum calcium concentrations. This results in inhibition of cardiac and vascular smooth muscle contraction, thereby widening the arterial lumen and reduction of blood pressure.

Dose/ Route: Initiate at 5 mg/hour IV increased by 2.5 mg/hour every 5 minutes to desired BP or a max of 15 mg/hour every 15 ​minutes,  may decrease to 3 mg/hour after response achieved
Onset of action: 5 – 10 minutes
Duration of action: 2–10 minutes (max, 8–12 hours)

Contraindications

Contraindications of nicardipine include:

• Hypersensitivity to nicardipine or other calcium-channel blockers
• Advanced aortic stenosis
• Compensatory hypertension, i.e. in case of an arteriovenous shunt or aortic coarctation
• Unstable angina
• Patients with rare hereditary problems of fructose intolerance should not take this medicine

Adverse effects

• Tachycardia
• Headache
• Flushing
• Local phlebitis (change infusion site after 12 hours)

8. Nitroglycerin

Nitroglycerin is an organic nitrate with arterial and venous vasodilator abilities used to treat hypertension (high blood pressure) during surgery or to control congestive heart failure in patients who have had a heart attack. It works by relaxing the blood vessels via dose-dependent dilation of arterial and venous beds to reduce both preload and afterload, and myocardial oxygen demand. Also, it improves coronary collateral circulation.

Nitroglycerin requires special delivery system owing to drug binding to polyvinyl chloride tubing.

Dose/ Route: 5 – 100 mcg/min IV infusion
Onset of action: 2 – 5 minutes
Duration of action: 5 – 10 minutes after D/C infusion

Contraindications

• Recent use (within several days) of phosphodiesterase type 5 inhibitor (PDE-5 inhibitors ) e.g., avanafil, sildenafil, tadalafil, or vardenafil may cause dangerously low hypotension; the time course of the interaction appears to be related to the PDE-5 inhibitor half-life
• Hypersensitivity to nitroglycerin or other nitrates or nitrites
• Symptomatic hypotension
• Uncorrected hypovolemia
• Increased intracranial pressure (head trauma, cerebral haemorrhage)
• Severe anaemia
• Constrictive pericarditis
• Pericardial tamponade
• Restrictive cardiomyopathy

Adverse effects

• Methemoglobinemia
• Tachycardia
• Nausea
• Headache
• Vomiting
• Methemoglobinemia
• Tolerance with prolonged use

9. Sodium nitroprusside

Sodium nitroprusside is a potent, effective, and readily reversible direct vasodilating agent indicated for immediate reduction of BP during hypertensive crisis. Intravenous administration of sodium nitroprusside rapidly decreases blood pressure by relaxing vascular smooth muscle to reduce afterload and preload.

Sodium nitroprusside is not suitable for direct injection; it requires dilution prior to infusion. The container should be wrapped with metal foil to prevent light-induced decompensation once reconstituted; the product will be a red-brown solution. Under these conditions, the solution is stable for 4 to 24 hours.

A rising BP may indicate loss of potency. A change in colour to yellow does not indicate effectiveness. The appearance of a dark brown, green, or blue colour indicates loss in activity. When changing to a new bag, the administration rate may require adjustment.

Dose/ Route: IV infusion.  Start: 0.5 mcg/kg/minute Usual: 2–5 mcg/kg/minute Max: 8 mcg/kg/minute
Onset of action: seconds
Duration of action: 3–5 minutes after D/C infusion

Contraindications

• Hypersensitivity
• Compensatory hypertension (eg, arteriovenous shunt or aortic coarctation); (for controlled hypotension): inadequate cerebral circulation
• Certain rare conditions, eg, congenital optic atrophy, tobacco amblyopia
• Treatment of acute CHF associated with reduced peripheral vascular resistance
• Not for use in emergency surgery in very ill patients

Adverse effects

• Nausea
• Vomiting
• Weakness
• Muscle twitching
• Sweating
• Chest pain
• Dizziness
• Headache
• Nasal congestion
• Arrhythmia
• Renal failure (thiocyanate toxicity)
• Hepatic impairment (cyanide toxicity)

Thiocyanate toxicity

Thiocyanate levels rise gradually in proportion to the dose and duration of administration. The half-life of thiocyanate is 2.7 days with normal renal function and 9 days in patients with renal failure. Toxicity occurs after 7 to 14 days in patients with normal renal function and after 3 to 6 days in renal failure patients.

Thiocyanate serum levels should be measured after 3 to 4 days of therapy, and the drug should be discontinued if levels exceed 10 to 12 mg/dL. Thiocyanate toxicity causes a neurotoxic syndrome of toxic psychosis, hyperreflexia, confusion, weakness, tinnitus, seizures, and coma.

Signs of cyanide toxicity

Signs of cyanide toxicity include lactic acidosis, hypoxemia, tachycardia, altered consciousness, seizures, and the smell of almonds on the breath. Concurrent administration of sodium thiosulfate or hydroxocobalamin may reduce the risk of cyanide toxicity in high-risk patients.

References

• CLEVIPREX® (clevidipine): Pharmacology and Mechanism of Action (n.d.). Retrieved from https://cleviprex.com/
• Nicardipine 10mg/10ml Solution for Injection (n.d.). Retrieved from https://www.medicines.org.uk/
• Nitroprusside Sodium (Rx) (n.d.). Retrieved from https://reference.medscape.com/
• Wells, B., DiPiro, J., Schwinghammer, T. and DiPiro, C. (2017). Pharmacotherapy Handbook. (10^th ed.). New York: McGraw-Hill Education.
• Whittlesea, C. and Hodson, K. (2019). Clinical Pharmacy and Therapeutics (6^th ed.). London: Elsevier Limited.
• Zeind, C. and Carvalho, M. (2018). Applied Therapeutics: The Clinical Use of Drugs (11^th ed.). New York: Wolters Kluwer.

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