Nitrates (Nitroglycerin, Isosorbide)

Summary

The drug class nitrates include the drugs nitroglycerin, isosorbide mononitrate, and isosorbide dinitrate.

They act as vasodilators, generally dilating the veins more than the arteries. Nitrates dilate the coronary arteries, bringing more blood and oxygen to the heart muscle. Nitrates lower both preload and afterload on the heart which decreases cardiac oxygen demand.

These mechanisms make nitrates useful in treating angina and myocardial infarctions, as well as heart failure.

As a side effect, nitrates may cause dizziness and patients should change positions slowly to avoid falls. If taken over a long period of time, patients can develop tolerance to nitrates. One common side effect is headache, which will usually diminish over time. Because nitrates increase intracranial pressure, they are contraindicated with head trauma. Nitrates can cause hypotension and for this reason are contraindicated with erectile dysfunction medications. Other side effects include reflex tachycardia and flushing.

Key Points

• Nitrates
  • Drug Names
    • Nitroglycerin
    • Isosorbide
      • Isosorbide mononitrate
      • Isosorbide dinitrate
  • Mechanism
    • Vasodilator
      • Dilates veins more than arteries
        • Decreases preload
          • Nitrates primarily dilate the veins, which causes a big decrease in preload
        • Decreases afterload
          • At high doses, nitrates also dilate the arteries and cause a slight decrease afterload
      • Dilates coronary arteries
        • Increases oxygen/blood supply to the heart
      • Decreases cardiac oxygen demand
        • Decreases the workload on the heart
  • Clinical Use
    • Treats angina and myocardial infarction (M.I.)
      • Long-acting forms (transdermal patch, topical ointment, etc.) are used to prevent chronic stable angina
      • Short-acting forms (sublingual tablet, translingual spray, etc.) are used to treat acute angina attacks
    • Treats chronic heart failure
  • Side Effects
    • Headache
      • This is a common, expected side effect. It is not a reason to call the doctor or stop taking the medication
      • Headache can be relieved with acetaminophen
      • Will likely diminish over time
      • Contraindicated with head trauma
        • Nitrates can increase intracranial pressure (ICP). Patients with head trauma (and other instances of increased ICP) should not take nitrates.
    • Hypotension
      • Due to its vasodilating effect
      • Check blood pressure prior to every dose and do not give if the patient is hypotensive
      • Contraindicated with sildenafil
        • Sildenafil and other PDE5 inhibitors are medications used to treat erectile dysfunction. It also has a strong vasodilating effect.
        • The combination of a nitrate with a PDE5 inhibitor can cause severe, life-threatening hypotension
    • Orthostatic hypotension (dizziness)
      • Patient should be sitting or lying down when taking this medication
      • Instruct patient to change positions slowly to avoid falls
    • Reflex tachycardia
    • Tolerance
      • With long-term use, the patient can quickly develop a tolerance, meaning the body will stop responding to the medication
    • Flushing
      • Facial flushing is due to vasodilation