Side Effects of Quinine
Quinine has several significant side effects including cinchonism (tinnitus, vertigo, headache, acute hearing loss), hypoglycemia, and cardiac arrhythmias, which can be serious and potentially life-threatening. 1
Common Side Effects
- Cinchonism: The most characteristic side effect complex of quinine, which includes tinnitus (ringing in ears), vertigo, headache, and potentially acute hearing loss 1
- Gastrointestinal effects: Nausea, vomiting, and digestive disorders are commonly reported 1
- Cardiovascular effects: QT interval prolongation, which can lead to serious arrhythmias 1, 2
- Hypoglycemia: Particularly concerning in pregnant women 2
Serious and Life-Threatening Side Effects
Cardiovascular Complications
- Quinine has Class I antiarrhythmic properties similar to quinidine, which can cause serious cardiac conduction abnormalities 2
- Potential cardiac effects include:
Neurological and Sensory Effects
- Visual disturbances: Can range from blurred vision and defective color perception to visual field constriction and permanent blindness in overdose cases 2, 4
- Hearing impairment: Temporary or permanent hearing loss has been documented, particularly with higher doses 5
- Central nervous system toxicity: Including drowsiness, disturbances of consciousness, ataxia, convulsions, respiratory depression, and coma 2
Hematologic Effects
- Severe hematologic reactions including cytopenias (low blood cell counts) 6
- Thrombocytopenia (low platelet count) 2
- Hemolytic-uremic syndrome in severe cases 6
Risk Factors for Adverse Effects
- Overdose: Many toxic reactions are dose-related, though some may be idiosyncratic 2
- Renal impairment: Clearance of quinine is decreased in patients with severe chronic renal failure 2
- Hepatic impairment: Quinine is not indicated in patients with severe hepatic impairment (Child-Pugh C) as drug clearance is decreased and half-life is prolonged 2
- Drug interactions: Concomitant use with medications that prolong QT interval or alter cardiac conduction 2
- Previous history: Prior serious CNS events increase risk of recurrence 7
Special Populations
- Pregnancy: Quinine can be used in all trimesters of pregnancy for malaria treatment, but carries risk of hypoglycemia 1, 2
- G6PD deficiency: Careful monitoring required as quinine may cause hemolysis in these patients 8
Monitoring Recommendations
- Cardiac monitoring: ECG monitoring is advisable, particularly in patients with existing cardiac conditions or electrolyte abnormalities 3
- Blood glucose monitoring: Particularly important in pregnant women 2
- Electrolyte monitoring: Hypokalemia can exacerbate cardiac effects 3
- Auditory and visual function: Should be assessed with prolonged use 5
Management of Toxicity
- Discontinuation of quinine upon onset of serious adverse effects 7
- Supportive care based on symptoms 4
- Specific interventions for arrhythmias may include antiarrhythmic medications 3
- Multiple-dose activated charcoal may decrease plasma quinine concentrations in overdose cases 2
Quinine is now rarely used as a first-line antimalarial agent due to its side effect profile, with artemisinin-based combinations being preferred for treatment of uncomplicated falciparum malaria 1.