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The biggest challenge facing highly antiretroviral-experienced patients and their caregivers is the diminishing number of therapeutic options available that sustain activity despite increasing numbers of drug-resistance mutations. New options in antiretroviral treatment have been introduced: two new members of traditional antiretroviral classes (darunavir and etravirine) and two drugs with novel mechanisms of action (raltegravir and maraviroc). Each was approved for use in treatment-experienced patients. A fifth drug-containing efavirenz, tenofovir, and emtricitabine (Atripla; Bristol-Myers Squibb, New York, NY, and Gilead Sciences, Foster City, CA)-is a novel coformulation of existing drugs from two different classes, simplifying administration with the intent of increasing adherence. Because successful management of HIV infection requires the simultaneous use of three or more drugs, understanding the pharmacologic aspects of coadministration is critical. This review summarizes the pharmacokinetic properties affecting the administration of these recently approved drugs in light of highly active antiretroviral treatment guidelines.

A sensitive and specific method for the quantitation of tenofovir (TFV) in human plasma by liquid chromatography/electrospray ionization mass spectrometry was developed and validated. Plasma samples were prepared by solid-phase extraction performed on Waters Oasis cation-exchange cartridges (30 mg). Chromatographic separation was performed isocratically on a reversed-phase Waters Atlantis dC18 column (2.0x100 mm, 3 microm). The mobile phase consisted of a hydroxylamine/acetic acid buffer (pH 6.75) and methanol (93:7, v/v). The acquisition was performed in selected ion monitoring mode for the protonated molecular ions [M+H]+ of m/z 288.2 for TFV and 212.2 for the internal standard, zalcitibine. The method was fully validated to determine its specificity, recovery, linearity and sensitivity, accuracy and precision. The analytical range was set at 1-750 ng/mL using a 200 microL plasma sample, with a mean coefficient of determination (r2) of 0.9969. The mean accuracies for the calibration standards ranged from -5.0 to 4.3%, while the precisions were within 1.2 and 6.4%. Intra-assay and inter-assay mean accuracies for three quality control concentrations (2, 60, and 600 ng/mL) ranged from -6.1 to 10.7%, while the precisions were within 1.3 and 9.1%. TFV was shown to be stable under normal storage and assay conditions; no degradation was seen when stored at -20 degrees C or -80 degrees C for up to 6 months, and after 16 h at room temperature in the injection matrix. The present method provides an accurate, precise, and sensitive tool for TFV quantitation and was successfully applied to an external proficiency-testing program and pharmacokinetic analysis., (Copyright (c) 2007 John Wiley & Sons, Ltd.)

Adenosine kinase (Ado kinase, EC 2.7.1.20) is a purine salvage enzyme that phosphorylates adenosine (Ado) to AMP. Ado kinase from Mycobacterium tuberculosis also catalyzes an essential step in the conversion of 2-methyl-Ado to a compound with selective antimycobacterial activity. In order to aid in the design of more potent and selective Ado analogs, eighty nucleoside analogs with modifications to the adenine (Ade) moiety of Ado were evaluated as both substrates and inhibitors of Ado kinase from M. tuberculosis, and a subset was further tested with human Ado kinase for the sake of comparison. The best substrates were 2-aza-Ado, 8-aza-9-deaza-Ado, and 2-fluoro-Ado and the most potent inhibitors were N1-benzyl-Ado (Ki=0.19 microM), 2-fluoro-Ado (Ki=0.5 microM), 6-cyclopentyloxy-purine riboside (Ki=0.15 microM), and 7-iodo-7-deaza-Ado (Ki=0.21 microM). These studies revealed the presence of a hydrophobic pocket near the N6- and N1-positions that can accommodate substitutions at least as large as a benzyl group. The ability to fit into this pocket increased the likelihood that a compound would be an inhibitor and not a substrate. The 2-position was able to accommodate exocyclic substitutions as large as a methoxy group, although substrate activity was low. Similarly, the 7-position could bind an exocyclic group as large as a carboxamido moiety. However, all of the compounds tested with modifications at the 7-position were much better inhibitors than substrates. MIC studies performed with selected compounds have yielded several Ado analogs with promising antitubercular activity. Future studies will utilize this information for the design of new analogs that may be selective antitubercular agents.

Adenosine kinase from Mycobacterium tuberculosis is the only prokaryotic adenosine kinase that has been isolated and characterized. The enzyme catalyzes the phosphorylation of adenosine to adenosine monophosphate and is involved in the activation of 2-methyladenosine, a compound that has demonstrated selective activity against M. tuberculosis. The mechanism of action of 2-methyladenosine is likely to be different from those of current tuberculosis treatments and this compound (or other adenosine analogs) may prove to be a novel therapeutic intervention for this disease. The M. tuberculosis adenosine kinase was overexpressed in Escherichia coli and the enzyme was purified with activity comparable to that reported previously. The protein was crystallized in the presence of adenosine using the vapour-diffusion method. The crystals diffracted X-rays to high resolution and a complete data set was collected to 2.2 Å using synchrotron radiation. The crystal belonged to space group P3121, with unit-cell parameters a = 70.2, c = 111.6 Å, and contained a single protein molecule in the asymmetric unit. An initial structural model of the protein was obtained by the molecular-replacement method, which revealed a dimeric structure. The monomers of the dimer were related by twofold crystallographic symmetry. An understanding of how the M. tuberculosis adenosine kinase differs from the human homolog should aid in the design of more potent and selective antimycobacterial agents that are selectively activated by this enzyme. [ABSTRACT FROM AUTHOR]