By William R. Condos, M.D.
Medical Director,
Cardiocascular Institute of the South /Lake Charles

In one of the more curious coincidences of science, the first modern high explosive -- nitroglycerin -- also became one of the very first man-made drugs. To this day, it remains the most commonplace treatment for chronic angina, the chest pain of heart disease.

Prior to the invention of nitroglycerin in the latter part of the last century, the handful of truly effective drugs, like aspirin, digitalis, morphine and quinine, were all derived from plant sources. Nitroglycerin -- glyceryl trinitrate -- doesn't exist in nature, which is hardly surprising, given its tendency to explode at the least provocation. In fact, until Alfred Nobel combined it with an inert binder and invented dynamite, its instability and explosive power made it probably the most hazardous compound that man had ever concocted.

So no one could have predicted that it would also prove to be a powerful vasodilator -- a drug which relaxes the smooth muscles of the blood vessels, permitting them to expand. That reduces the pumping force the heart must exert to circulate blood through the body. This reduction in the heart's workload relieves the crushing pain of angina, which result's from a shortage of oxygen to the heart muscle as a result of impaired circulation to the heart itself due to cholesterol plaque deposits inside the arteries.

While it would seem logical that the vasodilation would improve circulation to the heart by expanding the partially blocked arteries, that benefit is probably minimal. Nitroglycerin's effect is far more pronounced on the veins than the arteries.

Nitroglycerin tablets aren't swallowed. They are placed under the tongue and allowed to dissolve, permitting the drug to be absorbed into the body. (A very close relative, isosorbide dinitrate, is also used as a vasodilator, and is swallowed.)

Patients taking nitroglycerin have to interrupt their use of the drug for at least eight hours a day if it is to remain effective. And, for about half of the patients who take it, there is one unpleasant side effect -- severe headaches. The headaches tend to subside over time, however. In some patients, it can also produce dizziness from hypotension -- excessive lowering of blood pressure.

One bit of nonsense perpetrated by Hollywood is the idea that, unless the patient can get to his nitroglycerin tablets when he suffers an angina attack, it will become a fatal heart attack. Actually, patients are instructed that if angina isn't relieved by the nitroglycerin, they should seek immediate medical help, because the lack of relief may indicate that the pain is, in fact, caused by a heart attack, against which nitroglycerin has no effect whatever.

By the way, nitroglycerin, in pharmaceutical form, is not and cannot be rendered even slightly explosive.

&copy 1995 Cardiocascular Institute of the South

For further information, call Jane Arnette, Cardiocascular Institute of the South/Houma, 1-800-425-2565, or Jim Keyser at 1-800-848-2715. E-mail questions or comments to: jakeyser@cardio.com.

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