This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pharmacology
Patient was given chloroquine and doxycycline for 7 days. Patient's fever decreased in 4 days, but, peripheral smear showed occasional gametocytes of Plasmodium falciparum. This type of drug resistance is ? 
Select and explain. 
A. R1 type, B. R2 type, C. R3 type, D. R4 type
B: R2 type
Answer: B: R2 type 
Explanation: Ans. is 'b' i.e., R2 type WHO classification of antimalarial drug resistance 1. S-sensitive --> If a sexual parasites have cleared by day 6 from the begining of treatment wihout subsequent recrudescence until day 28. 2. R1-Low grade resistance --> Recrudescence of infection between 7-28 days of completing treatment. 3. R2 High grade resistance --> Reduction of parasitemia by more than 75% at 48 hours of completing treatment but failure to clear the organism within 7 days. 4. R3-> Parasitemia does not fall by more than 75% within 48 hours of completing treatment and there is no subsequant clearance of asexual parasites.