The first drug in the algorithm for unstable angina is oxygen. The second is nitroglycerin. Nitroglycerin has been in medical use since 1879 when it was noted that explosives workers had headaches during the week and chest pain on the weekends. It is an effective vasodilator, relaxing vascular smooth muscle. This leads to dilation of the arteries and veins, allowing more oxygen to reach the heart muscle and lowering the blood pressure which reduces the work of the heart. It has recently been discovered that nitric oxide is released with nitroglycerin use, which causes the well-known headaches associated as a side effect of its use.
NTG can be used for angina, hypertension, and congestive heart failure and comes in sublingual, extended release, ointment, buccal spray, and IV gtt. The sustained release capsules are used prophylactically and can lead to tolerance and physical dependence. I once had a patient who refused to give me his nitroglycerin tablets from home, despite repeated assurances that we would medicate him as needed. I later found a large stash of them in his sock! His misunderstanding of how the drug worked and his anxiety prevented us from effectively treating him. The physician, when told of this behavior, ordered he be allowed to have as many as he wanted. This only furthered the misinformation, but did alleviate the patientís anxiety. This type of dependence can be prevented by scheduling nitrate free periods with a physician.
During an acute episode of chest pain, the most common hospital therapy is the sublingual route, up to three tablets spaced five minutes apart. Before giving the first dose, be sure to have the patient describe the pain by location, intensity, radiation, and sensation. Also, many cardiologists want a 12 lead EKG before the nitroglycerin is given for diagnostic purposes. Obtain a blood pressure, be sure the patient is supine, and has moist mucosa. Instruct them to place the tab under their tongue and allow it to dissolve. Reevaluate their chest pain and blood pressure at the end of five minutes before administering the second dose. Give all three doses if that is what is required to completely alleviate the pain. If after three doses they are still having chest pain, call the physician to get orders for another line of treatment such as morphine or interventional cardiology.
Topical use requires measuring by the inch using special paper. Be sure you apply it directly to the anterior chest wall for a patient experiencing chest pain. For a patient without chest pain, it is acceptable to apply to the upper arm, unless ordered otherwise. It is important to write the time and amount applied on the outward facing paper. When removing nitroglycerin ointment, wear gloves and wipe off any remaining medication. Dispose of it in a sharps container to prevent accidental contact.
The new phosphodiesterase type 5 inhibitors, more commonly known as erectile dysfunction medications, are a contraindication for nitroglycerin usage. The reason for this is that phosphodiesterase type 5 inhibitors affect the PDE5 enzyme in vascular smooth muscle and this has a combined effect on dilation of the vessels due to the nitric oxide release. There are conflicting studies about how long this effect lasts, but the drug manufacturer recommendation is to wait 24 hours before using nitrates.