Quinine

 Common indications

• Quinine is commonly used for the treatment and prevention of night-time muscle cramp, but should really be reserved for cases when cramps regularly disrupt sleep and when non-pharmacological methods, such as passive stretching exercises, have failed.
• Quinine is a first-line treatment option for Plasmodium falciparum malaria.

 

Mechanisms of action

• Muscle cramp is caused by sudden, painful involuntary contraction of skeletal muscle. Quinine is thought to act by reducing the excitability of the motor end plate in response to acetylcholine stimulation. This reduces the frequency of muscle contraction. 
• In malaria, the mechanism of action of quinine is not well understood, but its overall effect leads to rapid killing of P. falciparum parasites in the schizont stage in the blood.

 

Important adverse effects

• Although quinine is usually safe at recommended doses, it is potentially very toxic and can be fatal in overdose. 
• It can cause tinnitus, deafness and blindness (which may be permanent), gastrointestinal upset, and hypersensitivity reactions. 
• Quinine prolongs the QT interval, and may therefore predispose to arrhythmias.  
• Hypoglycaemia can occur and can be particularly problematic in patients with malaria, which also predisposes to hypoglycaemia.

 

Warnings

• Quinine should be prescribed with caution in people with existing hearing or visual loss. 
• It is teratogenic, so should not be prescribed in the first trimester of pregnancy, although in the case of malaria its benefit may outweigh this risk. 
• Quinine should be avoided in people with G6PD deficiency, as it can precipitate haemolysis.

 

Important interactions

• Quinine should be prescribed with caution in patients taking other drugs that prolong the QT interval or cause arrhythmias such as amiodarone, antipsychotics, quinolones, macrolides, and SSRIs.