Quinine
Quinine is an optical isomer of quinidine. Quinine was once widely used for treatment of malaria and is still occasionally used for chloroquine-resistant cases. Quinine was formerly widely prescribed for the treatment of nocturnal muscle cramps, but an FDA advisory in 2006 warned that the modest benefits are outweighed by its potential to cause severe toxicity, and its use is no longer recommended for this indication. Quinine is found in tonic water and has been used to cut street heroin. It has also been used as an abortifacient.
Mechanism of toxicity
The mechanism of quinine toxicity is believed to be similar to that of quinidine (See Quinidine and Other Type IA Antiarrhythmic Drugs); however, quinine is a much less potent cardiotoxin.
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.
Pharmacokinetics (see Table II–61)
Toxic dose. 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.
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