I et efterfølgende randomiseret åbent studie (ESS100732) hos antiretroviral- naive patienter, viste fosamprenavir (700 mg) med samtidig administration med en lav- dosis ritonavir (100 mg) 2 gange daglig og en fast- dosis kombinationstablet af abacavir/ lamivudin (600 mg/ 300 mg) en gang daglig, at have sammenlignelig effekt over 48 uger med lopinavir/ ritonavir (400 mg/ 100 mg) givet 2 gange daglig i kombination med abacavir/ lamivudin (600 mg/ 300 mg en gang daglig).
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).