Pharmacology of Antianginal Nitrates and Nitrites

Key Pharmacological Agents

Different nitrate medications serve varying roles in the management of cardiovascular disease.

Nitroglycerin

Nitroglycerin is considered the most important drug for the symptomatic treatment of angina. It is unique because it can be used in both rapid-acting and long-acting formulations.

• Clinical Uses: Beyond angina, the intravenous form is used to control blood pressure in perioperative hypertension, heart failure, and hypertensive emergencies.
• Pharmacokinetics: It is subject to a large "first-pass effect" when taken orally, which is why sublingual or topical routes are preferred for rapid action.

Isosorbide Dinitrate and Isosorbide Mononitrate

These agents are also used for the treatment of angina and can be found in both rapid and long-acting forms.

• Isosorbide dinitrate: Functions in both acute and preventative capacities.
• Isosorbide mononitrate: This agent is primarily used as a long-acting form for the prevention of episodes.

Contraindications and Critical Drug Interactions

While effective, nitrates carry significant risks and strict contraindications that must be managed by healthcare providers.

Absolute Contraindications

Nitrates should not be administered to patients with:

• Known drug allergies.
• Severe anemia.
• Closed-angle glaucoma.
• Severe head injury.
• Hypotension (low blood pressure).

The PDE5 Inhibitor Interaction

A life-threatening contraindication exists for patients using erectile dysfunction (ED) medications. Nitrates must never be used in conjunction with:

• Sildenafil citrate (Viagra®)
• Tadalafil (Cialis®)
• Vardenafil hydrochloride (Levitra®)

The combination of these drugs can cause a profound and dangerous drop in blood pressure.

[!IMPORTANT] Exam Tip: If a patient asks if they can take their prescribed nitroglycerin after taking Viagra, the answer is a definitive NO. This interaction can lead to severe hypotension.

Adverse Effects and Nursing Implications

Patients using nitrates may experience several side effects. Common ones include:

• Headaches: These are frequent but usually diminish in intensity and frequency as the body adjusts to the medication.
• Reflex Tachycardia: The heart may beat faster to compensate for vasodilation.
• Postural Hypotension: A drop in blood pressure when changing positions, which can lead to dizziness or fainting.
• Tolerance: The body may become less responsive to the drug over time.

Nursing Care and Patient Teaching

To ensure safety, nurses should monitor for allergic reactions, hypotension, and dizziness. When teaching patients about sublingual nitroglycerin, emphasize the following:

1. Administration: Never chew or swallow sublingual tablets; they must be placed under the tongue.
2. Effectiveness: A burning sensation under the tongue indicates the drug is working.
3. Safety: Change positions slowly to avoid fainting due to postural hypotension.
4. Lifestyle: Limit caffeine, alcohol, and extreme heat (like hot baths or saunas), as these can exacerbate vasodilation and hypotension.