Quinine overdose can be associated with serious complications, including visual impairment, hypoglycemia, cardiac arrhythmias, and death. Visual impairment can range from blurred vision and defective color perception, to visual field constriction and permanent blindness. Cinchonism occurs in virtually all patients with quinine overdose. Symptoms range from headache, nausea, vomiting, abdominal pain, diarrhea, tinnitus, vertigo, hearing impairment, sweating, flushing, and blurred vision, to deafness, blindness, serious cardiac arrhythmias, hypotension, and circulatory collapse. Central nervous system toxicity (drowsiness, disturbances of consciousness, ataxia, convulsions, respiratory depression and coma) has also been reported with quinine overdose, as well as pulmonary edema and adult respiratory distress syndrome.

Most toxic reactions are dose-related; however some reactions may be idiosyncratic because of the variable sensitivity of patients to the toxic effects of quinine. A lethal dose of quinine has not been clearly defined, but fatalities have been reported after the ingestion of 2 to 8 grams in adults. Quinine, like quinidine, has Class I antiarrhythmic properties. The cardiotoxicity of quinine is due to its negative inotropic action, and to its effect on cardiac conduction, resulting in decreased rates of depolarization and conduction, and increased action potential and effective refractory period. ECG changes observed with quinine overdose include sinus tachycardia, PR prolongation, T wave inversion, bundle branch block, an increased QT interval, and a widening of the QRS complex. Quinine's alpha-blocking properties may result in hypotension and further exacerbate myocardial depression by decreasing coronary perfusion. Quinine overdose has been also associated with hypotension, cardiogenic shock, and circulatory collapse, ventricular arrhythmias, including ventricular tachycardia, ventricular fibrillation, idioventricular rhythm, and torsades de pointes, as well as bradycardia, and atrioventricular block (See WARNINGS, PRECAUTIONS, and ADVERSE EVENTS).

Quinine is rapidly absorbed, and attempts to remove residual quinine sulfate from the stomach by gastric lavage may not be effective. Multiple-dose activated charcoal has been shown to decrease plasma quinine concentrations (See CLINICAL PHARMACOLOGY/Extracorporeal elimination).

Forced acid diuresis, hemodialysis, charcoal column hemoperfusion, and plasma exchange were not found to be effective in significantly increasing quinine elimination in a series of 16 patients.

Prolonged QT Interval

Qualaquin is contraindicated in patients with a prolonged QT interval. One case of a fatal ventricular arrhythmia was reported in an elderly patient with a prolonged QT interval at baseline, who received quinine sulfate intravenously for P. falciparum malaria (See WARNINGS).

Glucose-6-Phosphate Dehydrogenase Deficiency

Qualaquin is contraindicated in patients with glucose-6-phosphate dehydrogenase (G-6-PD) deficiency (See WARNINGS).

Myasthenia Gravis

Qualaquin is contraindicated in patients with myasthenia gravis (See WARNINGS).

Hypersensitivity

Qualaquin is contraindicated in patients with known hypersensitivity to quinine. Qualaquin is also contraindicated in patients with known hypersensitivity to mefloquine or quinidine because cross-sensitivity to quinine has been documented (See PRECAUTIONS).

Qualaquin is contraindicated in patients with a history of potential hypersensitivity reactions associated with previous quinine use. These include, but are not limited to the following:

• Thrombotic thrombocytopenic purpura (TTP) or hemolytic uremic syndrome (HUS)
• Thrombocytopenia
• Blackwater fever (acute intravascular hemolysis, hemoglobinuria, and hemoglobinemia) (See PRECAUTIONS).

Optic Neuritis

Qualaquin is contraindicated in patients with optic neuritis (See ADVERSE REACTIONS).

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