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Quinine is an optical isomer of quinidine, a class Ia sodium channel blocking antidysrhythmic drug, with which it shares similar pharmacologic effects. Quinine is the primary alkaloid found in the bark of the cinchona tree and was once widely used for the treatment of malaria and is still occasionally used for chloroquine-resistant cases. A 2006 FDA advisory warned against the use of quinine in the treatment of nocturnal muscle cramps. Quinine is found in tonic water and has been used to cut street heroin. It has also been used as an abortifacient.


  1. The mechanism of quinine toxicity is believed to be similar to that of quinidine; however, quinine is a much less potent cardiotoxin.

  2. Quinine also has toxic effects on the retina that can result in blindness. At one time, vasoconstriction of retinal arterioles resulting in retinal ischemia was thought to be the cause of blindness; however, recent evidence indicates a direct toxic effect on photoreceptor and ganglion cells.

  3. Inhibition of potassium channels may result in impaired hearing, tinnitus and vertigo and hypoglycemia.

  4. Quinine has direct irritant effects on the gastrointestinal tract and stimulates CNS centers responsible for nausea and vomiting.

  5. Hypersensitivity reactions include urticaria, photosensitivity dermatitis, cutaneous vasculitis, angioedema, and thrombocytopenia ("cocktail purpura").

  6. Pharmacokinetics (see Table II–66)


Quinine sulfate is available in capsules and tablets containing 130–325 mg. The minimum toxic dose is approximately 3–4 g in adults; 1 g has been fatal in a child.


Toxic effects involve the cardiovascular and central nervous systems, the eyes, and other organ systems.

  1. Mild intoxication produces nausea, vomiting, and cinchonism (tinnitus, deafness, vertigo, headache, and visual disturbances).

  2. Severe intoxication may cause ataxia, confusion, obtundation, convulsions, coma, and respiratory arrest. With massive intoxication, quinidine-like cardiotoxicity (hypotension, QRS- and QT-interval prolongation, atrioventricular [AV] block, and ventricular arrhythmias) may be fatal.

  3. Retinal toxicity occurs 9–10 hours after ingestion and includes blurred vision, impaired color perception, constriction of visual fields, and blindness. The pupils are often fixed and dilated. Funduscopy may reveal retinal artery spasm, disc pallor, and macular edema. Although gradual recovery occurs, many patients are left with permanent visual impairment.

  4. Other toxic effects of quinine include hypokalemia, hypoglycemia, hemolysis (in patients with glucose-6-phosphate dehydrogenase [G6PD] deficiency), and congenital malformations when used in pregnancy.


Is based on a history of ingestion and the presence of cinchonism and visual disturbances. Quinidine-like cardiotoxic effects may or may not be present.

  1. Specific levels. Serum quinine levels can be measured by the same assay as for quinidine, as long as quinidine is not present. However, most hospital-based clinical laboratories no longer offer these assays. Plasma quinine levels above 10 mg/L have been associated with visual impairment; 87% of patients with levels ...

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