By Marven Ewen, MD
Medical Director

EMTs have several medications they can use to initiate treatment of various emergency medical conditions. It's important the EMT understands basics of the pharmacology of these interventions. When you understand how something works, as opposed to just memorizing it, you are more likely to remember the indications, contraindications and potential side effects. This article will review administration of aspirin (ASA) and nitroglyerin (nitro) for suspected myocardial infarction (MI).

ASA works by inhibiting platelet aggregation. That means the platelets can’t stick together to form a clot so it helps in preventing further clotting of a coronary artery. It is given orally and therefore takes time for it to be absorbed by the small intestine, pass through the liver metabolism, and then to the systemic circulation. Chewing it cuts down on the time it takes to get absorbed. The standard dose is either four 81 mg tablets or one 325mg tablet. You can guess what the main concern might be with this drug: because it interferes with platelet function it can increase the risk of bleeding. The area at most risk is the stomach because ASA, like other NSAIDs, also tends to thin the lining of the stomach when taken chronically. It would also not be given if there is active bleeding. Additionally, some asthmatics are particularly sensitive because ASA can cause bronchospasm. ASA is also a common patient allergy so it is important as with all drugs to rule this out before giving it. Note, ASA will not result in an immediate relief of chest pain nor would you expect to see any immediate changes in blood pressure or pulse.

Nitro on the other hand is a vasoactive drug. Unlike ASA, it doesn't affect clotting but rather dilates the blood vessels resulting in less work for the heart and reduced oxygen demand by the heart muscle. This medication is given under the tongue in spray or dissolvable tablet form. The standard dose is 0.4 mg every 5 minutes as needed and tolerated for up to 3 doses. The main concern with this medicine is that it can dramatically lower blood pressure. There can be a fatal drop in blood pressure if it is given within 24-48 hours of a sexually enhancing drug such as Viagra (depending on the duration of action of the drug). Also, don’t be confused if nitro doesn’t relieve the patient's chest pain. In the case of an MI, it often takes additional advanced treatments to relieve the pain. Further treatment will be initiated when the patient arrives at the ED.

Summary:

• Aspirin (ASA)
  • Indications: Signs and symptoms of MI
  • Dose and Route: Orally; 4 x 81 mg tabs or 1 x 325 mg tabs
  • Typical contraindications: Other daily NSAID use, anticoagulant or antiplatelet medication use, current or past GI bleeding or ulcers
  • Side effects: Increased risk of bleeding and stomach ulcers
  • Action: Inhibits further platelet aggregation during clot formation; does not reduce the pain associated with MI
• Nitroglycerin
  • Indications: Chest pain/discomfort in patient diagnosed with angina or past MI; signs and symptoms of MI or angina
  • Dose and Route: Sublingual spray or dissolving tablet; 0.4 mg every 5 minutes as needed up to 3 doses
  • Typical contraindications: Systolic blood pressure less than 90 mmHg; use of sexually enhancing medications
  • Side effects: Headache (minor); burning sensation under tongue (minor); significant drop in blood pressure (potentially life-threatening)
  • Action: Causes vasodilation which reduces the workload on the heart; may cause some relief of the pain of angina and MI