Zidovudine triphosphate and lamivudine triphosphate concentration-response relationships in HIV-infected persons.

OBJECTIVE: To quantitate intracellular concentrations of zidovudine and lamivudine triphosphate and explore relationships with virologic and immunologic responses to antiretroviral therapy. DESIGN: Eight antiretroviral-naive, HIV-infected persons with CD4 T cell counts > 100 x 10(6) cells/l, and HIV RNA in plasma > 5000 copies/ml participating in a prospective, randomized, open-label study of standard dose versus concentration-controlled therapy with zidovudine, lamivudine, and indinavir. METHODS: Peripheral blood mononuclear cells and plasma were collected frequently throughout the study for quantitation of intracellular zidovudine triphosphate and lamivudine triphosphate concentrations, and zidovudine and lamivudine concentrations in plasma. CD4 T cells and HIV RNA in plasma (Roche Amplicor Ultrasensitive Assay) were measured at baseline and every 4 weeks throughout the study. Relationships among intracellular and plasma concentrations, and CD4 T cells and HIV RNA in plasma were investigated with regression analyses. RESULTS: Significant relationships were observed between the intracellular concentrations of zidovudine triphosphate and lamivudine triphosphate and the baseline level of CD4 cells. Lamivudine triphosphate concentrations were related in a linear manner to the apparent oral clearance of lamivudine from plasma. A direct linear relationship was found between the intracellular concentrations of zidovudine triphosphate and lamivudine triphosphate. The percent change in CD4 cells during therapy and the rate of decline in HIV RNA in plasma were related to the intracellular concentrations of zidovudine triphosphate and lamivudine triphosphate. CONCLUSION: These studies into the intracellular clinical pharmacology of nucleoside reverse transcriptase inhibitors illustrate potential clinical implications as determinants of therapeutic success. Moreover, these findings provide several leads and a strong impetus for future investigations with nucleoside reverse transcriptase inhibitors particularly when given in combination and sequentially.

Simultaneous HPLC assay for quantification of indinavir, nelfinavir, ritonavir, and saquinavir in human plasma.

BACKGROUND: HIV protease inhibitors are recommended as part of combination antiretroviral therapy. Dual protease inhibitor therapy is also being used clinically. Consequently, a simultaneous assay for indinavir, nelfinavir, ritonavir, and saquinavir was developed. METHODS: Indinavir, nelfinavir, ritonavir, and saquinavir were extracted from plasma (250 microL) with methyl-t-butyl ether at basic pH after addition of an internal standard (A-86093). The compounds were separated on a Keystone BetaBasic C4 column (250 x 3 mm i.d.) at 40 degrees C with a mobile phase of acetonitrile-50 mmol/L ammonium formate buffer, pH 4.1 (52:48, by volume) at a flow rate of 0.5 mL/min. Indinavir, nelfinavir, ritonavir, and the internal standard (A-86093) were detected at 218 nm, and saquinavir was detected at 235 nm. The method was validated by analysis of five triplicate analyses of calibrators along with quality-control samples at three different concentrations prepared in human plasma. RESULTS: The extraction recovery was 87-92%. Within-run accuracy for quality-control samples was 6-8%, with CVs of 2-8%. Limits of quantification were 40-50 microg/L for indinavir, nelfinavir, and ritonavir, and 20 microg/L for saquinavir. Cross-validation with a liquid chromatography-mass spectroscopy method for saquinavir and nelfinavir was conducted with patient samples. Regression analysis revealed a good correlation (r(2) >0.94) between methods. Larger variations at concentrations >4000 microg/L were observed with nelfinavir. Interference with drugs commonly used in AIDS patients was not observed. Pharmacokinetic profiles for two patients on dual protease therapy were determined. CONCLUSIONS: A reliable and rugged simultaneous HPLC assay for four HIV protease inhibitors was developed. The assay method is convenient for clinical laboratories involved in therapeutic drug monitoring for HIV protease inhibitors. The assay has enough sensitivity to conduct pharmacokinetic studies in patients taking more than one HIV protease inhibitor along with other antiretroviral medications.

Concentration-controlled zidovudine therapy.

BACKGROUND: Heterogeneity in the response to antiretroviral therapy has been attributed to pharmacologic, immunologic, and virologic differences between patients. Currently available antiretroviral agents used for the treatment of human immunodeficiency virus (HIV) infection in adults are administered in standard fixed doses. The active moiety of nucleoside anti-HIV drugs is the intracellular anabolite. Therefore the heterogeneity in response to nucleoside agents may arise as a result of pharmacologic variability at both the systemic and cellular level. OBJECTIVES: To determine whether a novel concentration-controlled zidovudine regimen could improve anti-HIV response compared with the standard fixed-dose approach. DESIGN: At the Outpatient Clinic of the General Clinical Research Center at the University of Minnesota, 20 persons with HIV infection received an oral regimen of zidovudine designed to achieve a target concentration in plasma of 0.7 mumol/L and the 500 mg/day standard dose in a randomized, crossover 24-week study. RESULTS: The concentration-controlled regimen achieved overall higher systemic concentrations with reduced interpatient variability: steady-state average zidovudine plasma concentrations were 0.76 mumol/L (coefficient of variation, 12%) versus 0.62 mumol/L (coefficient of variation, 32%) for the standard regimen. There was no difference in safety and tolerance between regimens. Intracellular zidovudine triphosphate concentrations averaged 160 fmol/10(6) peripheral blood mononuclear cells (PBMCs) with concentration-controlled versus 92 fmol/10(6) PBMCs for standard therapy. The percentage change from baseline in CD4 cells was a 22% increase for the concentration-controlled regimen versus a 7% decrease with standard therapy. CONCLUSIONS: These data indicate that pharmacologic variability affects antiretroviral response. Furthermore, these findings provide a framework to characterize the pharmacologic determinants of effect and quantitate their contribution to the heterogeneity in clinical response to optimize therapeutic benefit.

Prodrugs of nitroxyl as potential aldehyde dehydrogenase inhibitors vis-a-vis vascular smooth muscle relaxants.

The synthesis and the chemical/biological properties of N-hydroxysaccharin (1) (2-hydroxy-1,2-benzisothiazol-3(2H)-one 1,1-dioxide), a nitroxyl prodrug, are described. When treated with 0.1 M aqueous NaOH, 1 liberated nitroxyl (HN=O), a known inhibitor of aldehyde dehydrogenase (AlDH), in a time-dependent manner. Nitroxyl was measured gas chromatographically as its dimerization/dehydration product N2O. Under these conditions, Piloty's acid (benzenesulfohydroxamic acid) also gave rise to HNO. However, whereas Piloty's acid liberated finite quantities of nitroxyl when incubated in physiological phosphate buffer, pH 7.4, formation of nitroxyl from 1 was minimal. This was reflected in the differential inhibition of yeast AlDH (IC50 = 48 and > 1000 microM) and the differential relaxation of preconstricted rabbit aortic rings in vitro (EC50 = 1.03 and 14.0 microM) by Piloty's acid and 1, respectively. The O-acetyl derivative of 1, viz., N-acetoxysaccharin (13a), was much less active in both assays. It is concluded that N-hydroxysaccharin (1) is relatively stable at physiological pH and liberates nitroxyl appreciably only at elevated pH's. As a consequence, neither 1 nor its O-methyl (8a) and O-benzyl (8b) derivatives were effective AlDH inhibitors in vivo when administered to rats at 1.0 mmol/kg.

Carbethoxylating agents as inhibitors of aldehyde dehydrogenase.

N,O-Dicarbethoxy-4-chlorobenzenesulfohydroxamate (1c) and O-carbethoxy-N-hydroxysaccharin (6), both potential carbethoxylating agents, inhibited yeast aldehyde dehydrogenase (AlDH) with IC50's of 24 and 56 microM, respectively. The esterase activity of the enzyme was commensurably inhibited. AlDH activity was only partially restored on incubation with mercaptoethanol (20 mM) for 1 h. On incubation with rat plasma, 1c liberated nitroxyl, a potent inhibitor of AlDH. Under the same conditions, nitroxyl generation from 6 was minimal, a result compatible with a previous observation that nitroxyl generation from N-hydroxysaccharin (7), the product of the hydrolysis of the carbethoxy group of 6, was minimal at physiological pH. Since chemical carbethoxylating agents represented by the O-carbethoxylated N-hydroxyphthalimide, 1-hydroxybenzotriazole, and N-hydroxysuccinimide (8, 9, and 10, respectively) likewise inhibited yeast AlDH, albeit with IC50's 1 order of magnitude higher, we postulate that 1c and 6 act as irreversible inhibitors of AlDH by carbethoxylating the active site of the enzyme.