The hypothesis of this study is that the level of adherence necessary to achieve HIV virologic suppression with a ritonavir boosted protease inhibitor regimen (i.e. lopinavir/ritonavir) is less than the 95% rate observed in the published literature with unboosted regimens.

The existing dogma is that patients receiving highly active antiretroviral therapy (HAART) to treat their HIV infection must take at least 95% of prescribed doses in order to maintain full suppression of viral replication. This belief is largely based on a single study that was performed between 1997 and 1999 (Ann Int Med 2000;133:21-30). The vast majority of patients in this study were receiving regimens based on either indinavir, nelfinavir, ritonavir, or saquinavir. All of these agents have relatively short half-lives, and therefore must be taken on time two or three times per day. Newer medications such as lopinavir/ritonavir (Kaletra) feature much more favorable pharmacokinetic profiles. On the basis of improved pharmacokinetics, there is reason to believe that regimens built around such agents may be more forgiving of missed medication doses.

This study aims to enroll 90 patients from the MMC I.D. Clinic who are either receiving or are about to receive Kaletra. Patients who agree to participate will be furnished with a MEMS cap, a bottle cap that electronically records each time that the bottle is opened and stores the data for computer download, and will undergo electronic monitoring of their Kaletra adherence for a period of siz months. Adherence data will not be reviewed during the study, but at study end (and at interim time points), the investigators will analyze the MEMS cap data from patients who have completed the study in order to determine the threshold value of adherence necessary to achieve satisfactory rates (i.e. 70-80%) of complete virologic suppression.

An additional aim of the study is to collect specimens from patients receiving Kaletra based regimens who experience virologic failure and to archive them for possible studies of genotypic and phenotypic resistance in the future.

Inclusion Criteria:

• HIV infection
• Receiving twice daily Kaletra at an FDA approved dosage
• Age>18 years
• CD4 and viral load available within seven day of enrollment
• Patient willingness to accept MEMS cap monitoring
• HIV genotype within 60 days of enrollment for patients with viral load>1000
• Patient willingness to grant informed consent and complete five study visits

Exclusion Criteria:

• Provider or patient deem it unlikely that Kaletra therapy will continue for the ensuing 24 weeks
• Prescription of any medication that is contraindicated for Kaletra recipients

Subjects will be recruited from the Montefiore Medical Center Infectious Diseases Clinic with eligibility criteria as listed below.