The value of lignocaine and phenytoin as antiarrhythmic drugs was discovered mainly by chance after their introduction for other purposes:(27) the local anesthetic lignocaine was shown to have antiarrhythmic properties during cardiac catheterization of patients,(25) while phenytoin's effects on the heart were first observed during its clinical trial for epilepsy.(26)
Nitroglycerine (or glyceryl trinitrate) is still considered one of the most effective remedies for the pain of angina even though it was developed over a hundred years ago. During the 1870s, the young London physician William Murrell became interested in a current medical controversy about the effects of nitroglycerin, which some doctors thought might be useful to treat spasms and nervous disorders. Murrell decided to make up his own mind and tested the drug on himself.6 He noticed that its actions were similar to those of amyl nitrite, a treatment for angina. Murrell argued that nitroglycerin could also be valuable for the same condition, a conclusion that has stood the test of time.
The quinidine story illustrates an important therapeutic principle - that an alert physician can discover important new uses for drugs originally introduced for an entirely different purpose. Examples include new treatments for depression, epilepsy, schizophrenia and Parkinson's Disease.(27) In addition, three of the four major classes of drugs used to treat high blood pressure were not known to have this effect until after they were given to patients for other conditions.(4) For instance, the beta-blocking drug propranolol was first marketed for treating cardiac arrhythmias, and then angina, but was soon found to lower blood pressure in patients, an unexpected discovery.(27) This observation led to the use of beta-blockers as one of the major treatments for high blood pressure.
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