In a subsequent randomised open-label study (ESS100732) in antiretroviral naïve patients, fosamprenavir (700 mg) co-administered with low dose ritonavir (100 mg) in a twice daily regimen including abacavir / lamivudine (600 mg / 300 mg) fixed dose combination tablet once daily showed comparable efficacy over 48 weeks to lopinavir / ritonavir (400 mg / 100 mg) given twice daily in combination with abacavir / lamivudine (600 mg / 300 mg once daily).