[Evidence-based therapeutic drug monitoring for saquinavir]. / Niveau de preuve du suivi therapeutique pharmacologique du saquinavir.

The human immunodeficiency virus (HIV) protease inhibitor saquinavir displays a large inter-individual variability in its pharmacokinetic parameters, related to a low absorption rate and an important hepatic metabolism. Based on literature, is the saquinavir therapeutic drug monitoring relevant? In naïve HIV-infected patients, the probability of achieving an undetectable HIV viral load at W48 was significantly associated with a saquinavir plasma trough concentration >100 ng/mL. Two studies in HIV-infected pre-treated patients reported that the genotypic inhibitory quotient was a predictive factor of virologic response with a threshold value around 40 ng/mL/mutation. Concerning the exposure-toxicity relationship, the risk of occurrence of grade 3-4 abdominal pains was more frequently associated with high concentrations of saquinavir, but without threshold value determination. Several studies, one of which was randomized, have reported the interest of saquinavir therapeutic drug monitoring to optimize the virologic response. Therefore, the level of evidence of the interest of saquinavir therapeutic drug monitoring is "recommended".

Maraviroc: in vitro assessment of drug-drug interaction potential.

AIMS: To characterize the cytochrome P450 enzyme(s) responsible for the N-dealkylation of maraviroc in vitro, and predict the extent of clinical drug-drug interactions (DDIs). METHODS: Human liver and recombinant CYP microsomes were used to identify the CYP enzyme responsible for maraviroc N-dealkylation. Studies comprised enzyme kinetics and evaluation of the effects of specific CYP inhibitors. In vitro data were then used as inputs for simulation of DDIs with ketoconazole, ritonavir, saquinavir and atazanvir, using the Simcyptrade mark population-based absorption, distribution, metabolism and elimination (ADME) simulator. Study designs for simulations mirrored those actually used in the clinic. RESULTS: Maraviroc was metabolized to its N-dealkylated product via a single CYP enzyme characterized by a K(m) of 21 microM and V(max) of 0.45 pmol pmol(-1) min(-1) in human liver microsomes and was inhibited by ketoconazole (CYP3A4 inhibitor). In a panel of recombinant CYP enzymes, CYP3A4 was identified as the major CYP responsible for maraviroc metabolism. Using recombinant CYP3A4, N-dealkylation was characterized by a K(m) of 13 microM and a V(max) of 3 pmol pmol(-1) CYP min(-1). Simulations therefore focused on the effect of CYP3A4 inhibitors on maraviroc pharmacokinetics. The simulated median AUC ratios were in good agreement with observed clinical changes (within twofold in all cases), although, in general, there was a trend for overprediction in the magnitude of the DDI. CONCLUSION: Maraviroc is a substrate for CYP3A4, and exposure will therefore be modulated by CYP3A4 inhibitors. Simcyptrade mark has successfully simulated the extent of clinical interactions with CYP3A4 inhibitors, further validating this software as a good predictor of CYP-based DDIs.

Estimation of population pharmacokinetic parameters of saquinavir in HIV patients with the MONOLIX software.

In nonlinear mixed-effects models, estimation methods based on a linearization of the likelihood are widely used although they have several methodological drawbacks. Kuhn and Lavielle (Comput. Statist. Data Anal. 49:1020-1038 (2005)) developed an estimation method which combines the SAEM (Stochastic Approximation EM) algorithm, with a MCMC (Markov Chain Monte Carlo) procedure for maximum likelihood estimation in nonlinear mixed-effects models without linearization. This method is implemented in the Matlab software MONOLIX which is available at http://www.math.u-psud.fr/~lavielle/monolix/logiciels. In this paper we apply MONOLIX to the analysis of the pharmacokinetics of saquinavir, a protease inhibitor, from concentrations measured after single dose administration in 100 HIV patients, some with advance disease. We also illustrate how to use MONOLIX to build the covariate model using the Bayesian Information Criterion. Saquinavir oral clearance (CL/F) was estimated to be 1.26 L/h and to increase with body mass index, the inter-patient variability for CL/F being 120%. Several methodological developments are ongoing to extend SAEM which is a very promising estimation method for population pharmacockinetic/pharmacodynamic analyses.

The pharmacokinetics of saquinavir: a Markov chain Monte Carlo population analysis.

Saquinavir is an HIV proteinase inhibitor marketed as a treatment for HIV infection. The drug has potent (Ki approximately 0.1 nM) antiviral activity and acts by inhibiting the processing of gag and gag-pol polyproteins, thus blocking the maturation of replicated viral particles. By assuming standard two-compartment disposition kinetics in combination with a variety of absorption processes we have identified two structural models that perform well with respect to describing the pharmacokinetic behavior of saquinavir when administered to healthy human volunteers from various Phase I studies. These structural models have been implemented for population analysis of these Phase I data via the Bayesian Markov chain Monte Carlo approach. We conclude that saquinavir exhibits complex and highly variable behavior, but can be modeled adequately using a two-compartment zero-order absorption model. There is also an indication that saquinavir kinetics may be time-dependent.

Protease inhibitors for the treatment of human immunodeficiency virus infection.

The pharmacology, pharmacokinetics, efficacy, adverse effects, drug interactions, and dosage and administration of protease inhibitors are reviewed. Protease inhibitors are a novel class of drugs used for the treatment of human immunodeficiency virus (HIV) infection. Saquinavir, ritonavir, indinavir, and nelfinavir have been approved in the United States; several other agents are under development. Protease inhibitors selectively block HIV protease, an enzyme involved in the later stages of HIV replication. Various pharmacokinetic differences exist among these agents, including differences in bioavailability, protein binding, and drug interactions. The drugs undergo extensive hepatic metabolism; dosage adjustments should be considered for patients with hepatic dysfunction. Clinical trials have shown protease inhibitors to be effective in reducing HIV RNA levels and increasing CD4+ lymphocyte counts. When protease inhibitors are used in combination with other antiretroviral agents, an additional beneficial effect on these markers occurs. Adverse effects of saquinavir and nelfinavir include mild gastrointestinal disturbances such as diarrhea. Ritonavir is less well tolerated because of gastrointestinal disturbances and circumoral and peripheral paresthesia. Indinavir has been associated with nephrolithiasis and asymptomatic hyperbilirubinemia. The development of resistance to protease inhibitors may be related to suboptimal dosages, noncompliance, or partial compliance. Protease inhibitors are potent and highly selective agents that block a critical step in HIV replication. They are effective and relatively well tolerated, but they are expensive, have extensive drug interaction profiles, and require careful compliance with the prescribed regimen.

Fortovase approved: new saquinavir formulation.

AIDS: The Food and Drug Administration (FDA) approved Fortovase, the new soft gel formulation of saquinavir, for treating HIV infection in adults. The gel delivers much more of the drug to the blood than the previous dosage form. The primary side effects are diarrhea, nausea, and abdominal discomfort. A new U.S. trial designed to compare Fortovase taken three times a day versus twice a day is now accruing patients. Contacts are provided for more information on this trial.^ieng