Atovaquone acts against ubiquinol-cytochrome c oxidoreductase (complex III), inhibits electron transport and collapses mitochondrial membrane potential, which is required for a number of parasite biochemical processes ( Vaidya, 2001 ). [jeb.biologists.org]

Agranulocytosis; aplastic anemia; hypersensitivity reactions like rashes, fixed drug eruptions, erythema multiforme of the Steven Johnson type, exfoliative dermatitis, serum sickness; liver dysfunction; anorexia, vomiting and acute hemolytic anemia can [malariasite.com]

Methemoglobinemia is a complication that may be associated with high-dose regimens of quinine or the derivatives chloroquine and primaquine. [24] A patient presenting with cyanosis and a normal PaO 2 on room air should be suspected of having methemoglobinemia [emedicine.medscape.com]

Cardiovascular effects have been recorded with bradycardia and sinus arrhythmia being consistently recorded in 68% of patients treated with mefloquine (in one hospital-based study). [en.wikipedia.org]

Less frequently it can cause nightmares, sleeping disturbances, dizziness, ataxia, sinus bradycardia, sinus arrhythmia, postural hypotension, and an ‘acute brain syndrome’ consisting of fatigue, asthenia, seizures and psychosis. [malariasite.com]

Some cardiac changes were reported during a clinical trial, notably non specific ST changes and a first degree atrioventricular block (these disappeared when the patients recovered from the malarial fever). [en.wikipedia.org]