Antimalarial agents should not be taken by anyone who has had a previous reaction to using the drug. In addition, patients who have a G6PD (glucose-6-phosphate dehydrogenase) deficiency should not take antimalarial drugs such as chloroquine, isoniazid or primaquine, which is sometimes used to treat patients infected with a specific Plasmodium parasite that can lie dormant in the liver. A screening test is available to help determine whether or not patients have this deficiency.

Other conditions that may prevent use of antimalarial agents include:

• Myasthenia gravis (neuromuscular disorder characterized by muscle weakness)
  
  
• Psoriasis
  
  
• Retinal changes or changes to visual field
  
  
• Severe blood disease
  
  
• Alcoholism
  
  
• Significant liver dysfunction
  
  
• Significant neurological disorders
  
  
• Auditory damage

In addition, antimalarials may not be recommended for women who are pregnant, planning to become pregnant or breastfeeding.