Cinchonism, also known as quinism, is a term for a series of disease-like symptoms that result from an overdose of quinine, an alkaloid compound C20H24N2, that is derived from cinchona bark of the C. calisaya tree and bush species mainly used to treat drug resistant cases of malaria. While cinchonism usually occurs from excessive amounts of quinine taken either as a drug or through direct ingestion of cinchona bark, it can also be caused by exposure to much smaller quantities of quinine over a protracted duration. The most common symptoms occurring from an antimalarial drug dosage or long-term exposure to quinine includes repeated headaches and nausea; tinnitus, which produces a sensation like ringing in the ears; or more serious hearing impairment including deafness. More rare cases of adverse effects from cinchonism include anaphylactoid shock; photophobia, or sensitivity to light; and mental conditions like dullness and confusion.
Two other possible exposure methods can result in cinchonism symptoms. Tonic water that contains a small amount of quinine to give it a slightly bitter taste can cause cinchonism, or the taking of quinidine sulfate, a drug used to treat heart conditions like ventricular arrhythmia. While tonic water with quinine is usually safe, drinking such water over a long period of time is theorized to lead to ill effects. Anti-arrhythmic drugs are subject to causing the same level of serious adverse effects from exposure that taking quinine in antimalarial drugs is. Drugs like quinidine sulfate, however, have their own additional list of possible side effects, such as blurred vision, potential allergic reactions, and a yellowing of the skin.
The antimalarial drug dosage can also have a direct effect on how serious the possible symptoms of cinchonism are. A standard therapeutic dosage can cause nausea, hearing, and vision problems, and various mental states of uneasiness. While these symptoms are reversible and will fade with cessation of taking the drug, more serious side effects like blindness, renal failure, and death from cardiotoxicity can occur with higher dosages. Quinine can also have the tragic side effect in high doses of causing birth defects or being an abortifacient, meaning that spontaneous abortions can take place in pregnant women who take the drug as a malaria treatment.
The safety of an antimalarial drug varies considerably based on the health of the patient and the dosage. In some cases, only a single dose is necessary to cause adverse effects. One of the reasons for this is that quinine causes certain enzymes to become inactive within mammalian cells, which can have both positive and negative results. It reduces inflammation, which makes antimalarial drugs useful for treating arthritis, but it can also cause a form of muscle disease generally categorized as myopathy. These multiple symptoms of cinchonism make it necessary for doctors to evaluate giving quinine on a case-by-case basis and to closely monitor the patient for any possible adverse events.