The purpose of this study is to study and compare the pharmacokinetics profile of low dose raltegravir (RAL) (400mg OD and 800mg OD) and standard dose of 400mg BID in Thai HIV-infected patients.

Twenty four HIV-infected volunteers on stable doses of RAL 400 mg BID for at least 3 months and with undetectable viral load will be enrolled. On Day 1, all 24 subjects will attend the first intensive PK collection for RAL 400 mg BID and the blood samples will be drawn at T = 0.0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 4.0, 6.0, 8.0, 10.0, and 12.0 hour post medication. All 24 subjects will be randomised (1:1) to either Group A (RAL 400 mg OD) or Group B (RAL 800 mg OD) for 14 days. On day 15, a second 24 hour intensive PK will be carried out and the blood samples will be drawn. After 2nd intensive PK, the subjects will switch to the other dosing regimen. Subjects in group A will receive RAL 800 mg OD and group B will receive RAL 400 mg OD for another 14 days. On day 29, the third 24 hour intensive PK will be carried out. After the 3rd intensive PK, all 24 subjects will be switched back to the initial regimen of RAL 400 mg BID.

Inclusion Criteria:

• Signed informed consent
• Evidence of HIV infection
• Age> 18 years
• On RAL 400 mg BID containing HAART regimen with a VL < 50 copies for at least 3 months before enrollment
• Willing to adhere to the protocol requirements

Exclusion Criteria:

• Evidence of RAL resistance
• History of RAL allergy
• Use of concomitant medication that may interfere with the pharmacokinetics of RAL
• Current pregnancy or lactating or planning to get pregnant
• Active drug abuse or alcoholic
• Relevant history or current condition, illness that might interfere with drug absorption, distribution, metabolism or excretion.