The purpose of this study is to study amprenavir/ritonavir, saquinavir/ritonavir or efavirenz in HIV-infected patients following failure with Kaletra (ABT-378/ritonavir) as their first protease inhibitor based HAART.

Inclusion:

• Remain on present anti-HIV drugs during screening until a new regimen is started.
• Have a viral load of at least 1,000 copies/ml on the 2 most recent tests after at least 24 weeks of lopinavir/ritonavir and while still on it.
• Have an HIV which shows reduced susceptibility to lopinavir.
• Are at least 18 years old.
• Are not presently ill.
• Have not been treated for an opportunistic infection within 30 days of screening.
• Agree not to take certain drugs and agree to inform and get permission from the doctor before taking any medicines, over the counter medicines, herbal medicines, alcohol or recreational drugs.
• Agree to use an accepted barrier method of birth control.

Exclusion:

• Female subject is pregnant or lactating.
• Have taken any protease inhibitor other than lopinavir/ritonavir for more that two weeks.
• Are taking chemotherapy.
• Have a medical problem with their pancreas.
• Have been screened for this study within the past 12 weeks.
• Appear to be unsuitable in the opinion of the doctor.