(Spirit of Nitroglycerin.)

Definition. - An alcoholic solution containing 1 per cent. by weight of glyceryl trinitrate.

Origin. - Nitroglycerin is obtained by gradually adding dehydrated glycerin to a mixture of nitric and strong sulphuric acid, the nitroglycerin formed being washed with water and dilute soda solution to remove all acid.

Description and Properties. - Nitroglycerin occurs as a clear colorless liquid possessing the odor and taste of alcohol. It should be tasted and handled with great caution, since it is apt to produce violent headache, whether ingested or applied to the skin. It explodes with great force, and should be kept in a cool place, remote from lights or fire.

Dose. - 1-3 minims (0.06-0.18 Cc.) of the spirit [1 minim (0.05 Cc), U. S. P.].

The action of nitroglycerin is very similar to that of amyl nitrite, although it is less prompt, while more persistent. Nitroglycerin produces a frontal headache of much greater intensity than that caused by amyl nitrite. This is also true of sodium nitrite, though the headache it occasions is less severe than that resulting from nitroglycerin.

Nitroglycerin is preferable to amyl nitrite for internal administration.

Therapeutics. - Externally and Locally. - The nitrites are not used for external purposes.

Internally. -The property of amyl nitrite in suddenly lowering arterial pressure and dilating the arterioles renders it of inestimable value as a relief for the terrible precordial pain in angina pectoris.

Epileptic seizures may often be aborted by the instant inhalation of amyl nitrite upon the first indication of the aura epileptica. The drug has also been successfully employed for the relief of asthma, particularly the uremic form, as well as for cardiac dyspnea and puerperal eclampsia.

Like many other motor depressants, it has been used in the treatment of tetanus and strychnine-poisoning. It has proved an efficient preventive for the chill occurring in virulent malarial fever, and has served as a valuable antidote in poisoning from chloroform.

The drug is indicated in all conditions of high arterial tension, as in chronic nephritis, etc. It is also beneficial in congestive dysmenorrhea.

The sodium nitrite is used for the same purposes as the amyl nitrite, though superior to it for internal administration, as in cases of abnormally high arterial tension.

Nitroglycerin is specially adapted for the treatment of cardiopathies occurring after middle life. It is useful in chronic nephritis with high arterial tension, and, associated with digitalis, is recommended in certain cases of pneumonia. The tendency to increase of peripheral resistance in the vessels after adult life is attained renders possible the favorable administration of doses of nitroglycerin intolerable in early life.

The drug is often of marked benefit in the arrhythmia of slightly enlarged and degenerated hearts with arteriosclerosis. It is also of considerable value in relieving the pseudo-anginas which are frequently a feature of vascular disease. It should be given in doses of 1/200 to 1/100 grain (0.00032-0.0006 Gm.) twice or four times daily.

It is fair to say, however, that recent experiments by H. P. Loomis show that high arterial pressure in man is not perceptibly affected by nitroglycerin nor its dilatation of the blood-vessels apparent. The usual dose of 1/100 grain (0.0006 Gm.) is too small to produce any effect in pathologic conditions; 1/40 grain (0.0015 Gm.) is a minimum dose. Even in large and repeated doses the author has never seen any ill effects. It is doubtful if the urine is increased in quantity in chronic Bright's disease by this drug. In conditions due to arterial spasms, so called, such as angina pectoris, migraine, asthma, nitroglycerin may be of benefit in full doses, often repeated, but not in arterial sclerosis, where the arteries themselves are more or less changed.

Vaquez calls attention to the variability of the action of the drug. Its vasodilating action is totally absent in a large number of cases, even in comparatively large doses. In only exceptional cases can its action be regarded as identical with amyl nitrite.

The effects of nitroglycerin are so transitory that in order to maintain a more or less continuous effect on the circulation the drug should be given at frequent intervals. To affect arterial tension in chronic conditions erythrol tetranitrate is unquestionably the more efficacious drug.

Osier recommends the prolonged administration of nitroglycerin in locomotor ataxia, affirming that it lessens the frequency of the crises and relieves the neuralgic pains.

The drug is of use in sciatica, and frequently relieves obstinate hiccough. It has been recommended for the same diseases for which amyl nitrite is used.