This will be an open-label, 3-period, fixed sequence study in young, healthy, male and female subjects of the pharmacokinetic interaction between raltegravir and Kaletra.

This will be an open-label, 3-period, fixed sequence study in young, healthy, male and female subjects. The initial cohort, to be studied simultaneously, will be 15 subjects with intention to collect complete data from 12 subjects. Replacements will be subsequently enrolled if necessary. Subjects will be reimbursed.

The periods will be

• Period 1: Raltegravir (RAL) 400 mg q12h for 4 days (7 doses of RAL).
• Period 2: Kaletra 200 mg 2 pills bid for 10 days (19 doses of Kaletra).
• Period 3: both regimens for 4 days (7 doses of both drugs). All morning doses will be observed at Prism Research, Inc. Evening doses will be distributed each morning. 12 hour PK studies will be done on the last day of each period. Specimens will be obtained 0, 0.5, 1, 1.5, 2, 3, 4, 5, 6, 8, 10, 12 hours after the morning dose of the last dosing day of each period.

Inclusion Criteria:

• Healthy, male or female, age 18-55.
• Anti-HIV, anti-HCV, HBsAg negative.
• Normal history and physical at screening.
• Normal complete blood count, creatinine and ALT at screening.
• Negative urine pregnancy test at screening.
• BMI 18-30.

Exclusion Criteria:

• Donated blood in the month before Day 1.
• Participated in another research study in the month before Day 1.
• Tobacco use in the 3 months before Day 1, unwillingness to avoid tobacco use during the study.
• Use of any illegal drug in the year before Day 1, positive drug screen for an illegal drug at screening.
• Unwillingness to restrict coffee use to 6 or fewer cups of coffee during the study.
• Unwillingness on the part of fertile female subjects to be abstinent or to use two effective birth control methods, one of which is a barrier method, for any vaginal intercourse.
• Unwillingness to avoid use of any prescribed medication during the study
• Allergy to RAL, lopinavir or ritonavir.