Quinine: Dose-dependent effects on QT interval and drug interactions

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Quinine is indicated for treatment of nocturnal leg cramps. Quinine is well known to have effects on QT interval. A  2017 routine EU review  recommended that warnings for dose-dependent QT-prolonging effects should be present in the product information for all quinine-containing medicines. Use caution if prescribing quinine medicines in patients with

  • with conditions that predispose to QT prolongation such as pre-existing cardiac disease or electrolyte disturbance
  • taking other medicines that could prolong the QT interval
  • with atrioventricular block

Quinine is metabolised via hepatic oxidative cytochrome P450 pathways, predominantly by CYP3A4. The 2017 review identified a pharmacokinetic study reporting that serum levels of phenobarbital or carbamazepine could become raised when these anticonvulsant drugs are used concomitantly with quinine. Although data is limi...