QUININE, the most important alkaloid contained in cin chona bark (see CINCHONA, ALKALOIDS OF).
Physiological Action.—Our knowledge of this subject is mainly due to Professor Binz of Bonn. Quinine is a bactericide, many bacteria being killed by a .2% solution, but is more definitely poisonous to minute animal organisms especially malarial parasites.
The first feature of the internal action of quinine is its intensely bitter taste. This induces a reflex secretion from the salivary and gastric glands, followed or accompanied by increased vascu larity of the gastric mucous membrane, and some activity of the muscular wall of the stomach. This means that the appetite is strengthened, and digestion rendered more rapid and complete. In this sense alone quinine is a tonic.
The action of quinine on the blood itself—quite apart from its action on malarial blood—is of great complexity and importance. Whilst it is not a haematinic, in that it does not increase the num ber of the red blood corpuscles, it very markedly influences the stability of the compounds of the haemoglobin with oxygen. Like alcohol and prussic acid, quinine interferes with oxidation, so that oxyhaemoglobin is relatively unable to give up its oxygen to the tissues, the metabolism of which is therefore greatly modified. This property is doubtless partly—though not wholly—explana tory of the antipyretic action of quinine.
The action of quinine on the circulatory apparatus is not marked. It is only in very large doses that it weakens the intra cardiac nervous ganglia, slows and weakens the pulse, and dan gerously lowers the blood pressure. Similarly the depressant action on the respiratory centre in the medulla oblongata occurs only after the administration of enormous doses.
The action of quinine on the temperature is important, for it is the safest of all known antipyretics. Its action on the normal temperature is nil. The drug is not an antithermal. But when the temperature is raised, quinine will frequently lower it. The action is not due to any influence on the thermic centres, nor to any pro duction of diaphoresis, but to the influence of quinine upon the stability of oxyhaemoglobin. Quinine was the first antipyretic used.
In some of the lower vertebrates quinine reduces the activity of the spinal cord, but in the human species it appears to stimulate the nervous mechanism of the uterus and it is therefore included under the class of oxytocic or ecbolic drugs.
Therapeutics.—The supreme value of quinine is as a specific antidote to malaria, against which it also possesses a powerful prophylactic action. Ten or fifteen grains of the sulphate are often given three times a day for this latter purpose, and smaller doses of the much more efficacious acid hydrochloride convey even more certain immunity. In treating malaria with this drug certain important facts are to be observed. Quinine administered by the mouth or by any other means will soon enter the blood, and will then kill the haematozoon malariae, whether it be contained within corpuscles or free in the blood-plasma. There is one excep tion, however. Quinine is apparently powerless to kill the organism when it is in its reproductive phase. This phase corresponds to the pyretic attack. It is therefore useless to administer quinine during a malarial paroxysm. Two successful methods may be adopted. The quinine may be given in a single large dose-3o grains of the sulphate or 20 of the acid hydrochloride—an hour or two before the attack is due, i.e. just before the parent organism i.1 the red blood corpuscles is about to discharge the new genera tion of young parasites into the blood-plasma. An equally effective method, which may be combined with the above, is to give the quinine in io-grain doses of the acid hydrochloride every four hours between the attacks. Whichever method be adopted, the paroxysm that was expected will probably not appear.
Quinine is largely used as a bitter tonic in doses of about half a grain. The acid hydrochloride is the best salt to employ. It has some analgesic power, and is a safe and often efficient drug in the treatment of neuralgia, even when the patient has not had malaria.
Cinchonism is the name applied to the congeries of toxic symp toms which follow the prolonged administration of quinine, but may appear after one small dose in certain persons. The symptoms closely resemble those of salicylism, and also, though in less degree, those of carbolism. The patient is deaf, but complains of ringing in the ears, which may assume various forms, especially in musical people. In persons who display a pronouriced idiosyncrasy towards cinchonism, the symptoms may often be successfully averted if small doses of hydrobromic acid-1 o minims of the dilute solu tion—are given with the quinine.