Reported rates of drowsiness ( 12.5 % compared with 30 % ; P = .01 ; number needed to treat to benefit , 6 ) , xerostomia ( 10.0 % compared with 23.8 % ; P < .01 ; number needed to treat to benefit , 8 ) , and persistent ketonuria at 24 hours ( 12.5 % compared with 30 % ; P = .01 ; number needed to treat to benefit , 6 ) were less frequent with ondansetron .