29 serious adverse events occurred in 26 ( 8 % ) of 329 patients ; QT prolongation was the most common serious adverse event ( 11 [ 3 % ] of 329 ) , occurring in five ( 2 % ) of 225 patients receiving tafenoquine , four ( 8 % ) of 50 patients receiving primaquine , and two ( 4 % ) of 54 patients receiving chloroquine alone , with no evidence of an additional effect on QT of chloroquine plus tafenoquine coadministration .