Measurement of Plasma and Intracellular Concentrations of Raltegravir

• Concentrations of RAL in blood cells. [ Time Frame: one month ] [ Designated as safety issue: No ]
  Analyze and compare plasma and intracellular concentrations of RAL in blood plasma and in peripheral blood mononuclear cells, using high performance liquid chromatography (HPLC).
  
  
• Concentrations of RAL in blood plasma. [ Time Frame: one month ] [ Designated as safety issue: No ]
  Analyze and compare plasma and intracellular concentrations of RAL in blood plasma and in peripheral blood mononuclear cells, using high performance liquid chromatography (HPLC).
  
  

• Pharmacokinetic variability of plasma concentrations of the drug. [ Time Frame: one month ] [ Designated as safety issue: No ]
  To determine the pharmacokinetic variability of plasma and intracellular concentrations of the drug.
  
  
• Pharmacokinetic variability of intracellular concentrations of the drug. [ Time Frame: one month ] [ Designated as safety issue: No ]
  To determine the pharmacokinetic variability of plasma and intracellular concentrations of the drug.
  
  
• Trough concentrations of the drug when dosed twice daily versus once daily. [ Time Frame: one month ] [ Designated as safety issue: No ]
  To compare pharmacokinetics of the drug when dosed twice daily versus once daily.
  
  
• Pharmacokinetics of the drug when dosed twice daily versus once daily. [ Time Frame: One month ] [ Designated as safety issue: No ]
  To compare pharmacokinetics of the drug when dosed twice daily versus once daily.
  
  

Integrase strand transfer inhibitors are one of the newest class of antiretroviral drugs. This class of drugs inhibit the catalytic activity of HIV-1 integrase, an HIV-1-encoded enzyme required for viral replication [1]. Inhibition of integrase prevents covalent insertion of unintegrated, linear HIV-1 DNA into the host cell genome, therefore preventing the formation of HIV-1 provirus. RAL, the first agent in its class, was initially approved in 2007 for use in patients harboring drug-resistant HIV [2]. More recently, the FDA has expanded the indication for RAL use in HIV-infected patients who are antiretroviral naïve [3]. The currently approved dose is 400 mg twice daily. The RAL area-under-the-curve (AUC) and Cmax increase in a dose-dependent fashion over the range of 100 mg to 1,600 mg. With twice-daily dosing, PK steady state is achieved within approximately the first 2 days. Considerable variability was observed in the PK of raltegravir in clinical trials. In clinical trial participants receiving twice-daily RAL 400 mg, drug exposures were characterized by a geometric mean AUC within the first 12 hours of 14.3 mcM(hr) and a plasma concentration at 12 hours of 142 nM [3]. RAL at concentrations of 6 to 50 nM resulted in 95% inhibition (EC95) of viral spread in mitogen-activated human peripheral blood mononuclear cells (PBMCs) infected with diverse, primary clinical isolates of HIV-1, including isolates resistant to reverse transcriptase inhibitors and protease inhibitors (PIs).

The absolute bioavailability of RAL has not been established. RAL is approximately 83% bound to human plasma protein over the concentration range of 2 to 10 mcM. The apparent terminal half-life of RAL is approximately 9 hours, with a shorter alpha-phase half-life (about 1 hour), accounting for much of the AUC. Determination of drug levels to guide treatment of HIV infection is available for protease inhibitors (PI) and non-nucleoside reverse transcriptase inhibitors (NNRTI) but is not yet considered standard of care [4,5]. RAL is associated with potent performance against HIV in treatment-naïve patients and those with limited treatment options, potentially because of its binding interaction with the HIV preintegration complex. When RAL binds to the complex, the drug dissociates at a rate slower than the half-life of the complex itself, which makes binding essentially irreversible. Thus, the efficacy of RAL may be dependent on intracellular binding levels of the drug to the preintegration complex, rather than on the plasma concentrations of RAL. Because of this, we postulate that intracellular concentrations of RAL are more likely to correlate with biological activity against HIV. Moreover, if pharmacokinetic behavior can be predicted, and depending on the trough concentrations observed, the drug might be suitable for different dosing approaches including once a day administration. This would create more flexibility for patients, and the chance to improve adherence.