The mean duration of gametocyte carriage was 6.6 days ( 95 % CI 5.3-7 .8 ) in the 0.75 mg/kg reference group , 6.3 days ( 5.1-7 .5 ) in the 0.4 mg/kg primaquine group ( p = 0.74 ) , 8.0 days ( 6.6-9 .4 ) in the 0.1 mg/kg primaquine group ( p = 0.14 ) , and 12.4 days ( 9.9-15 .0 ) in the placebo group ( p < 0.0001 ) .