Nitrates: Nursing pharmacology

Nitrates are medications that come under the umbrella of a larger group called vasodilators, which dilate the walls of blood vessels. Nitrates are primarily used to treat angina pectoris, which is pain caused by reduced blood flow to the heart muscle; as well as hypertension, and heart failure. More recently, they’ve also been approved for the topical treatment of anal fissures.

The most commonly used nitrates include nitroglycerin, isosorbide dinitrate, and isosorbide mononitrate. Out of these, nitroglycerin has a rapid and short-lasting action, so when treating acute anginal pain or hypertension, it is typically given through rapidly absorbable routes like sublingual, oral spray, or intravenously, to bypass the first-pass metabolism in the liver, which would slow its absorption. For long-term prevention, though, routes of administration can include transdermal patches, topical ointments, or extended-release oral capsules. Nitroglycerin can also be administered rectally for the treatment of anal fissures.

On the other hand, isosorbide dinitrate and isosorbide mononitrate have a longer duration of action and are typically administered orally as tablets or sustained-release capsules, which makes them useful for the long-term prevention of angina pectoris, or to treat clients with heart failure.

Once absorbed into the blood, nitrates quickly get converted into their active form, called nitric oxide. Nitric oxide diffuses to the smooth muscle cells of both veins and arteries, causing wall relaxation and vasodilation.

The result of venous vasodilation is peripheral blood pooling, which in turn decreases the return of venous blood to the heart. This way, nitrates predominantly reduce preload, which is the pressure that stretches the heart as it fills with blood from venous return.

At the same time, arterial vasodilation lowers the systemic vascular resistance, which will also reduce the afterload, or the pressure that the heart must work against to eject the blood. Ultimately, by reducing preload and afterload, nitrates reduce the amount of work the heart has to do, eventually decreasing the heart’s oxygen consumption.

Nitrates also have a minor effect on the dilation of the coronary arteries, which helps increase oxygen delivery to heart tissue.

Common side effects of nitrates include headache, dizziness, flushing, nausea and vomiting. Another important side effect of nitrates is orthostatic hypotension, where the blood pressure falls significantly when the client stands up too quickly. As a result, these clients could experience lightheadedness or syncope due to decreased blood flow to the brain.

In addition, clients may experience reflex tachycardia, which is caused by the sympathetic system triggering an increase in heart rate in response to the hypotension caused by nitrates, in order to maintain tissue perfusion.

Now, clients who continuously use nitrates soon develop tolerance to these side effects. Unfortunately, clients may also develop tolerance to the therapeutic effects of nitrates, especially with uninterrupted use; clients can prevent this by avoiding using nitrates for several hours each day.

Finally, nitrates are contraindicated in individuals with hypotension, hypovolemia, severe anemia, and cardiomyopathy. Nitrates should be used carefully during pregnancy or breastfeeding, as well as in clients with increased intracranial pressure or cerebral hemorrhage, renal or hepatic disease, and syncope.