Use of Qualaquin for Treatment or Prevention of Nocturnal Leg Cramps

Qualaquin may cause unpredictable serious and life-threatening hypersensitivity reactions, QT prolongation, serious cardiac arrhythmias including torsades de pointes, and other serious adverse events requiring medical intervention and hospitalization. Fatalities have also been reported. The risk associated with the use of quinine sulfate in the absence of evidence of its effectiveness for treatment or prevention of nocturnal leg cramps, outweighs any potential benefit in treating and/or preventing this benign, self-limiting condition (See CONTRAINDICATIONS, PRECAUTIONS, and ADVERSE REACTIONS).

QT Prolongation and Ventricular Arrhythmias

QT interval prolongation has been a consistent finding in studies which evaluated electrocardiographic changes with oral or parenteral quinine administration, regardless of age, clinical status, or severity of disease. The maximum increase in QT interval has been shown to correspond with peak quinine plasma concentration (See CLINICAL PHARMACOLOGY/Electrocardiogram). Quinine sulfate has been rarely associated with potentially fatal cardiac arrhythmias, including torsades de pointes, and ventricular fibrillation.

Qualaquin is not recommended for use with other drugs known to cause QT prolongation, including Class IA antiarrhythmic agents (eg, quinidine, procainamide, disopyramide), and Class III antiarrhythmic agents (eg, amiodarone, sotalol, dofetilide).

Quinine may also inhibit the metabolism of other drugs that are CYP3A4 substrates known to cause QT prolongation, such as astemizole, cisapride, terfenadine, pimozide, halofantrine, and quinidine. Torsades de pointes has been reported in patients who received concomitant quinine and astemizole. Therefore, concurrent use of quinine sulfate with these medications, or drugs with similar properties, should be avoided (See PRECAUTIONS/Drug Interactions).

Concomitant administration of quinine sulfate with the antimalarial drugs, mefloquine or halofantrine, may result in electrocardiographic abnormalities, including QT prolongation, and increase the risk for torsades de pointes or other serious ventricular arrhythmias. Concurrent use of quinine sulfate and mefloquine may also increase the risk of seizures (See PRECAUTIONS/Drug Interactions).

The use of macrolide antibiotics such as erythromycin should be avoided in patients receiving quinine sulfate. Fatal torsades de pointes was reported in an elderly patient who received concomitant quinine, erythromycin, and dopamine. Although a causal relationship between a specific drug and the arrhythmia was not established in this case, erythromycin is a CYP3A4 inhibitor and could potentially increase quinine plasma levels when used concomitantly. A related macrolide antibiotic, troleandomycin, has been shown to increase quinine exposure in a pharmacokinetic study (See PRECAUTIONS/Drug Interactions).

Qualaquin should also be avoided in patients with known prolongation of QT interval (See CONTRAINDICATIONS), in elderly patients, and in patients with clinical conditions known to prolong the QT interval, such as uncorrected hypokalemia, bradycardia, and certain cardiac conditions.

Concomitant Use of Rifampin

Treatment failures may result from the concurrent use of rifampin with quinine sulfate, due to decreased plasma concentrations of quinine, and concomitant use of these medications should be avoided (See PRECAUTIONS/Drug Interactions).

Glucose-6-Phosphate Dehydrogenase (G-6-PD) Deficiency:

Hemolysis and hemolytic anemia can occur in patients with G-6-PD deficiency who receive quinine. Qualaquin should be stopped immediately upon the appearance of evidence of hemolysis (See CONTRAINDICATIONS).

Myasthenia gravis

Quinine sulfate has neuromuscular blocking activity, and may exacerbate muscle weakness in patients with myasthenia gravis (See CONTRAINDICATIONS).

Neuromuscular Blocking Agents

The use of neuromuscular blocking agents should also be avoided in patients receiving quinine sulfate. In one patient who received pancuronium during an operative procedure, subsequent administration of quinine resulted in respiratory depression and apnea. Although there are no clinical reports with succinylcholine or tubocurarine, quinine may also potentiate neuromuscular blockade when used with these drugs (See PRECAUTIONS/Drug Interactions).