|Classification and external resources|
Cinchonism or quinism is a pathological condition in humans caused by an overdose of quinine or its natural source, cinchona bark. Quinine is medically used to treat malaria. In much smaller amounts, quinine is an ingredient of tonic drinks, acting as a bittering agent. Cinchonism can occur from therapeutic doses of quinine, either from one or several large doses. Quinidine (Class 1A anti-arrhythmic) can also cause cinchonism symptoms to develop with as little as a single dose.
Signs and symptoms 
Symptoms of mild cinchonism (which may occur from standard therapeutic doses of quinine) include flushed and sweaty skin, ringing of the ears (tinnitus), blurred vision, impaired hearing, confusion, reversible high-frequency hearing loss, headache, abdominal pain, rashes, drug-induced lichenoid reaction (lichenoid photosensitivity), vertigo, dizziness, dysphoria, nausea, vomiting and diarrhea.
Large doses of quinine may lead to severe symptoms of cinchonism: skin rashes, deafness (reversible), somnolence, diminished visual acuity or blindness, anaphylactic shock, and disturbances in cardiac rhythm or conduction, death from cardiotoxicity. Quinine may also trigger a rare form of hypersensitivity reaction in malaria patients termed blackwater fever that results in massive hemolysis, hemoglobinemia, hemoglobinuria, and renal failure.
Most symptoms of cinchonism (except in severe cases) are reversible and disappear once quinine is withdrawn.
Quinine, like chloroquine, inactivates enzymes in the lysosomes of cells, and has an anti-inflammatory effect, hence its use in rheumatoid arthritis. However switching off these enzymes can also cause abnormal accumulation of glycogen and phospholipids in lysosomes, causing a toxic myopathy. It is possible this is the root cause of cinchonism.
- Dawson, T. A. (1995). "Side effect of quinine for nocturnal cramps" (pdf). British Medical Journal 310 (6981): 738. doi:10.1136/bmj.310.6981.738a. PMC 2549119. PMID 7711556.
- IPCS INTOX databank entry for quinine
- Effects of Quinine on the Excitability and Voltage-Dependent Currents of Isolated Spiral Ganglion Neurons in Culture