To Determine if There Are Pharmacokinetic Interactions at Plasma or Intracellular Level Between Nucleosides and Tenofovir

Determination of Plasma and Intracellular Levels of Nucleoside Reverse Transcriptase Inhibitors (NRTI) and of Nucleotide Analog Tenofovir Disoproxil Fumarate (TDF) in Patients Treated With Abacavir and/or Lamivudine Given With or Without TDF.

The purpose of this study is to evaluate if there are pharmacokinetic interactions between the NRTI 3TC and ABV, and the TDF nucleotide. For this purpose, the intracellular and plasma levels of 3TC and ABV will be compared in patients given these nucleosides with TDF and 30 days after the interruption of the TDF.

There is clear evidence of pharmacokinetic interaction between ddI+TDF. However, the interaction between TDF and other NRTIs, mainly at intracellular level, has not been so well studied.

Since all the NRTIs are anabolized at intracellular level by numerous kinases, and are transported by passive carrier systems, the interaction may be between TDF and other NRTIs.

This study aims to investigate the pharmacokinetic interactions between the TDF and the nucleosides abacavir (ABV) and lamivudine (3TC) at plasma and intracellular level.

With this objective, intracellular and plasma levels will be analysed in a group of patients that receive the combinations 3TC +TDF, ABV+TDF and 3TC+ABV+TDF together with lopinavir/rtv or nevirapine. Subsequently, in a second phase of the study, in the group of patients given ABV and/or 3TC + TDF + lopinavir/rtv, the pharmacokinetic determinations will be repeated after a 4-week interruption of the TDF .

Inclusion Criteria:

1. HIV+ patients aged above 18 years.
2. Undetectable HIV viral load in the last determination
3. Patients capable of correct compliance according to clinical criteria.
4. Patients on triple HAART therapy for the previous 3 months including 3TC and/or ABV and TDF, with a PI (Lopinavir/ritonavir) or an NNRTI (Nevirapine)
5. Women may not be of fertile age (defined as at least one year from menopause or undergoing any surgical sterilisation technique), or must undertake to use a barrier contraceptive method during the study.
6. Ability to provide informed consent.

Exclusion Criteria:

1. Incorrect therapeutic compliance over the four weeks before the beginning of the study.
2. Interruption or withdrawal from therapy during follow-up.
3. Concomitant treatment with any drug which according to the clinician's criterion may interact with the investigational antiretrovirals, such as other antiretrovirals.
4. Triple HAART therapy including Nevirapine (for phase II)
5. Documented or suspected resistance to ABV, 3TC or lopinavir/rtv (for phase II).