Among previously untreated patients who received three direct-acting antiviral agents ( with the ABT-450 / r dose administered as 150 mg of ABT-450 and 100 mg of ritonavir ) plus ribavirin , the rate of sustained virologic response at 24 weeks after treatment was 88 % among those who received the therapy for 8 weeks and 95 % among those who received the therapy for 12 weeks ( difference , -7 percentage points ; 95 % confidence interval , -19 to 5 ; P = 0.24 ) .