Renal excretion of apricitabine in rats: ex vivo and in vivo studies

Apricitabine (ATC) is a novel nucleoside reverse transcriptase inhibitor undergoing phase 2/3 clinical development for the treatment of HIV infection. In this investigation, the renal handling of ATC was evaluated in the isolated perfused rat kidney (IPK) model with follow-up in vivo studies. IPK experiments were performed to characterize the renal excretion of ATC, to probe mechanisms of ATC excretion using known inhibitors of organic cation (cimetidine) and organic anion (probenecid) transport systems, and to screen for potential drug-drug interactions between ATC and clinically relevant medications (dapsone, metformin, pentamidine, stavudine, tenofovir and ritonavir). ATC demonstrated net tubular secretion in the IPK with a baseline excretion ratio (XR) of 2.1 ± 0.56. ATC XR decreased 3.6-fold in the presence of cimetidine and 2-fold in the presence of probenecid. Among the clinically relevant medications, metformin produced the greatest inhibitory effect on ATC excretion. In vivo studies were conducted in rats to evaluate ATC disposition upon co-administration with compounds that showed a significant effect on ATC clearance in the IPK model. Co-administration of cimetidine and trimethoprim significantly reduced ATC renal clearance, but resulted in only a moderate increase in plasma exposure. Metformin had no apparent effect on ATC clearance in rats. These findings indicate that the IPK model is more sensitive to secretory inhibition as compared to in vivo. The medications screened showed minimal effects on ATC renal excretion in the IPK, and should thus be excluded as potential in vivo interactants. Overall, this study generated important information on renal handling of ATC to support its development and commercialization.

Apricitabine: a nucleoside reverse transcriptase inhibitor for HIV infection

OBJECTIVE

To review the pharmacology, pharmacokinetics, efficacy, and safety of apricitabine, a nucleoside reverse transcriptase inhibitor that is currently under investigation and has fast-track approval status with the Food and Drug Administration.

DATA SOURCES

A literature search was conducted using PubMed (1966-June 2009) to retrieve relevant material using the search terms apricitabine, SPD754, and AVX754. References from selected articles were evaluated to identify other pertinent trials. Information was also obtained from the manufacturer.

STUDY SELECTION AND DATA EXTRACTION

All English-language in vitro and in vivo studies and abstracts evaluating apricitabine were reviewed and considered for inclusion. Preference was given to human data.

DATA SYNTHESIS

Apricitabine is a prodrug that is phosphorylated to its active triphosphate form intracellularly, which ultimately results in chain termination and inhibition of reverse transcription. Apricitabine is administered orally, displays linear pharmacokinetics, and is renally excreted with minimal to no hepatic metabolism. It has demonstrated antiretroviral activity against drug-resistant strains both in vitro and in vivo. In clinical studies, in both antiretroviral-naïve and treatment-experienced patients, apricitabine achieved the primary endpoint of significant reductions in plasma viral load versus comparator. Further Phase 2 and 3 studies are currently enrolling. Safety analysis indicates that apricitabine is well tolerated and has a low potential for causing mitochondrial damage. The most common adverse events reported include headache and rhinitis. Development of resistance or further gene mutations has not been shown in clinical studies to date.

CONCLUSIONS

Although the role of apricitabine in the treatment of HIV-1 infection has yet to be established, its activity against resistant HIV-1 strains and its tolerability profile will likely make it a viable second-line treatment option in patients who have failed regimens containing lamivudine or emtricitabine.

Pharmacokinetics and drug-drug interactions of antiretrovirals: an update

Current antiretroviral treatment has allowed HIV infection to become a chronic manageable condition with many HIV patients living longer. However, available antiretrovirals are not without limitations, for example the development of resistance and adverse effects. Consequently, new drugs in existing and novel classes are urgently required to provide viable treatment options to patients with few remaining choices. Darunavir, etravirine, maraviroc and raltegravir have been recently approved for treatment-experienced patients and other agents such as rilpivirine, vicriviroc and elvitegravir are currently under phase III study. Clinical studies are necessary to optimise potential treatment combinations and to manage drug-drug interactions to help avoid toxicity or therapy failure. This review aims to summarise the pharmacokinetics and key drug-drug interaction studies for newly available antiretrovirals and those in development. Further information regarding drug-drug interactions of well established antiretrovirals and those recently approved are readily available online at sites such as http://www.hiv-druginteractions.org, http://www.clinicaloptions.com/hiv, http://hivinsite.ucsf.edu. This article forms part of a special issue of Antiviral Research marking the 25th anniversary of antiretroviral drug discovery and development, Vol 85, issue 1, 2010.