Pharmacokinetics (PK) Study of Once Daily Darunavir/Ritonavir and Twice and Once Daily Raltegravir in HIV-infected Subjects

The integrase inhibitor raltegravir has shown to a potent new agent for the treatment of HIV infection.

When raltegravir and darunavir/ritonavir have been combined in the Benchmark studies, they provided an excellent virological response in highly experienced patients.

Darunavir once daily use is increasing due to patients' preference for once daily regimens.

Raltegravir has not shown any pharmacokinetic/pharmacodynamic relationship and doses of 100 to 400 mg twice daily have shown similar virological responses. This may be due to intracellular drug accumulation.

However, data on the use of darunavir/r plus raltegravir once daily and on raltegravir intracellular concentrations are not available.

Whether raltegravir is efficacious when administered once daily is unknown. However, concentrations higher the IC95 of 33nM have been associated to a favourable virological response.

Therefore, we would like to investigate the plasma and intracellular pharmacokinetics of darunavir/ritonavir and raltegravir when co-administered once daily in order to provide further data to support the use of these agents once daily, patients' preferred dosing schedule.

Pharmacogenetics holds promise in HIV treatment because of the complexity and potential toxicity of multi antiretroviral drug therapies that are prescribed for long periods. Thus far, few candidate genes have been examined for a limited number of allelic variants, but a number of confirmed associations have already emerged.

From a public health perspective, as antiretroviral medications become increasingly available to racially and ethnically diverse populations worldwide, understanding the genetic structures of each population may allow us to anticipate the impact of adverse responses, even in groups that were not represented in drug registration trials.

The existing literature on pharmacogenetic determinants of antiretroviral drug exposure, drug toxicity, as well as genetic markers associated with the rate of disease progression underline the recent advances which occurred in the past few years.

However, it is expected that larger-scale comprehensive genome approaches will profoundly change the landscape of knowledge in the future. Additional studies are needed to assess the implications for long-term responses to antiretroviral agents.

For this reason we plan to collect a single blood sample from each participant in our intensive pharmacokinetic studies, such as this one, in order to be able to investigate the association between genetic polymorphisms in drug disposition genes (such as those encoding for cytochrome P450 isoenzymes or transmembrane transporters) and drug exposure. A candidate gene approach will be utilised to examine loci of interest. This procedure will provide potentially important information on genetic influences on plasma drug concentrations and give insight into how to improve the management of HIV-infected patients by individualising therapy. These studies will not be powered for genetic associations but will enable us to build a data base of genotype-phenotype. Prospective genetic studies would need to be planned based on these preliminary data.