Types of Drug Resistance In defining criteria for resistance to the aminoquinolineantimalarial drugs, the WHO has described three grades of resistance following treatment (Low grade) R1 : Recrudescence of infection between 7 and 28 days of completing treatment following initial resolution of symptoms and parasite clearance. (High grade) R2 : Reduction of parasitaemia by > 75% at 48 hours but failure to clear parasites
within 7 days. R3 : Parasitaemia does not fall by >75% within 48 hours. (www.slideshare.net)