(1/314) A multiple drug interaction study of stavudine with agents for opportunistic infections in human immunodeficiency virus-infected patients.

The effects of multiple opportunistic infection medications on stavudine pharmacokinetics were evaluated. Ten patients with CD4 counts of less than 200 cells/mm3 received stavudine (40 mg twice daily) in combination with one to three other drugs used to treat opportunistic infections. Serial blood samples for stavudine concentrations were collected after 1 week of therapy on each regimen and assayed for stavudine by using a validated high-pressure liquid chromatography method. Although the maximum concentration of drug in serum was significantly decreased when the drug was given in combination with three opportunistic infection medications, the area under the concentration-time curve did not significantly differ across various treatment regimens. Stavudine exposure was not significantly altered by multiple concomitant medications. Side effects were minor throughout the 3-month study period. The tolerability of stavudine, combined with its lack of drug interactions, makes it an attractive agent for use as part of a combination regimen.  (+info)

(2/314) Suppression of replication of multidrug-resistant HIV type 1 variants by combinations of thymidylate synthase inhibitors with zidovudine or stavudine.

The replication of recombinant multidrug-resistant HIV-1 clones modeled on clinically derived resistant HIV-1 strains from patients receiving long-term combination therapy with zidovudine (AZT) plus 2',3'-dideoxycytidine was found to regain sensitivity to AZT and stavudine (D4T) as a consequence of a pharmacologically induced decrease in de novo dTMP synthesis. The host-cell system used was phytohemagglutinin-stimulated peripheral blood mononuclear cells; dTMP and dTTP depletion were induced by single exposures to a low level of the thymidylate synthase inhibitor 5-fluorouracil (5-FU) or its deoxynucleoside, 2'-deoxy-5-fluorouridine. The host-cell response to the latter was biphasic: a very rapid decrease in the rate of de novo dTMP formation and, consequently, in intracellular dTTP pools, followed by slower recovery in both indices over 3 to 24 h. With the additional presence of AZT or D4T, however, replication of the multidrug-resistant HIV-1 strains remained inhibited, indicating dependence of HIV DNA chain termination by AZT-5'-monophosphate or 2',3'-didehydro-2', 3'-dideoxythymidine-5'-monophosphate in these resistant strains on simultaneous inhibition of host-cell de novo synthesis of thymidine nucleotides. No effect on viability of control (uninfected) phytohemagglutinin-stimulated/peripheral blood mononuclear cells was noted on 6-day exposures to 5-FU or 2'-deoxy-5-fluorouridine alone or in combination with AZT or D4T, even at drug levels severalfold higher than those used in the viral inhibition studies. These studies may provide useful information for the potential clinical use of AZT/5-FU or D4T/5-FU combinations for the prevention or reversal of multidrug resistance associated with long-term dideoxynucleoside combination therapy.  (+info)

(3/314) The ALBI trial: a randomized controlled trial comparing stavudine plus didanosine with zidovudine plus lamivudine and a regimen alternating both combinations in previously untreated patients infected with human immunodeficiency virus.

A total of 151 previously untreated patients infected with human immunodeficiency virus type 1 (HIV-1) with CD4 cell counts >/=200/microL and plasma HIV-1 RNA levels of 10,000-100,000 copies/mL were randomly assigned to 24 weeks of open-labeled stavudine plus didanosine (group 1), zidovudine plus lamivudine (group 2), or stavudine plus didanosine followed by zidovudine plus lamivudine (group 3). The mean decrease in HIV-1 RNA level was greater in group 1 (2.26 log10 copies/mL) than in groups 2 (1.26 log10 copies/mL) or 3 (1.58 log10 copies/mL; P<.0001). The mean increase in CD4 cell counts was greater in groups 1 (124 cells/microL) and 3 (118 cells/microL) than in group 2 (62 cells/microL; P=.02). All regimens were generally well tolerated. The combination of stavudine plus didanosine reduced plasma HIV-1 RNA concentrations and increased CD4 cell counts more effectively than did the combination of zidovudine plus lamivudine or the regimen alternating both combinations.  (+info)

(4/314) Levels of human immunodeficiency virus type 1-specific cytotoxic T-lymphocyte effector and memory responses decline after suppression of viremia with highly active antiretroviral therapy.

Therapeutic suppression of human immunodeficiency virus type 1 (HIV-1) replication may help elucidate interactions between the host cellular immune responses and HIV-1 infection. We performed a detailed longitudinal evaluation of two subjects before and after the start of highly active antiretroviral therapy (HAART). Both subjects had evidence of in vivo-activated and memory cytotoxic T-lymphocyte precursor (CTLp) activity against multiple HIV-1 gene products. After the start of therapy, both subjects had declines in the levels of in vivo-activated HIV-1-specific CTLs and had immediate increases in circulating HIV-1-specific CTL memory cells. With continued therapy, and continued suppression of viral load, levels of memory CTLps declined. HLA A*0201 peptide tetramer staining demonstrated that declining levels of in vivo-activated CTL activity were associated with a decrease in the expression of the CD38(+) activation marker. Transient increases in viral load during continued therapy were associated with increases in the levels of virus-specific CTLps in both individuals. The results were confirmed by measuring CTL responses to discrete optimal epitopes. These studies illustrate the dynamic equilibrium between the host immune response and levels of viral antigen burden and suggest that efforts to augment HIV-1-specific immune responses in subjects on HAART may decrease the incidence of virologic relapse.  (+info)

(5/314) Cell-associated HIV-1 RNA in blood as indicator of virus load in lymph nodes. The Swiss HIV Cohort Study.

We have developed sensitive assays for viremia and cell-associated human immunodeficiency virus type 1 (HIV-1) RNA and DNA to assess the predictive value of virological parameters determined in blood for virus load in lymph nodes (LNs). Eighteen patients were included; 13 received stavudine/didanosine/hydroxyurea and 5 stavudine/didanosine, and all had viremia <500 copies/mL for >3 months. At the time of LN biopsy (median, 10 months), the median viremia was 2.09 log copies/mL (range, <0.70-3.34). Cell-associated HIV-1 RNA and DNA were detectable in blood and LNs of all patients. The median cell-associated RNA and DNA were 2.16 log copies/106 cells and 2.60 log copies/106 cells in blood versus 4.31 log RNA copies/106 cells and 3.26 log DNA copies/106 cells in LNs. Regression analysis shows that, in treated patients with sustained low viremia, cell-associated RNA and DNA in blood are better predictors of virus load in LNs than viremia.  (+info)

(6/314) Characterization of the activation pathway of phosphoramidate triester prodrugs of stavudine and zidovudine.

The phosphoramidate triester prodrugs of anti-human HIV 2', 3'-dideoxynucleoside analogs (ddN) represent a convenient approach to bypass the first phosphorylation to ddN 5'-monophosphate (ddNMP), resulting in an improved formation of ddN 5'-triphosphate and, hence, higher antiviral efficacy. Although phosphoramidate derivatization markedly increases the anti-HIV activity of 2',3'-didehydro-2', 3'-dideoxythymidine (d4T) in both wild-type and thymidine kinase-deficient CEM cells, the concept is far less successful for the 3'-azido-2',3'-dideoxythymidine (AZT) triesters. We now investigated the metabolism of triester prodrugs of d4T and AZT using pure enzymes or different biological media. The efficiency of the first activation step, mediated by carboxylesterases, consists of the formation of the amino acyl ddNMP metabolite. The efficiency of this step was shown to be dependent on the amino acid, alkyl ester, and ddN moiety. Triesters that showed no conversion to the amino acyl ddNMP accumulated as the phenyl-containing intermediate and had poor, if any, anti-HIV activity. In contrast to the relative stability of the triesters in human serum, carboxylesterase-mediated cleavage of the prodrugs was found to be remarkably high in mouse serum. The subsequent conversion of the amino acyl ddNMP metabolite to ddNMP or ddN was highest in rat liver cytosolic enzyme preparations. Although L-alaninyl-d4TMP was efficiently converted to d4TMP, the main metabolite formed from L-alaninyl-AZTMP was the free nucleoside (AZT), thus explaining why d4T prodrugs, but not AZT prodrugs, retain anti-HIV activity in HIV-infected thymidine kinase-deficient cell cultures. The rat liver phosphoramidase responsible for the formation of ddNMP was shown to be distinct from creatine kinase, alkaline phosphatase, and phosphodiesterase.  (+info)

(7/314) Use of recombinant viruses to assess the pattern of early human immunodeficiency virus breakthrough infection in the presence of stavudine.

A variety of cell lines were infected with replication-defective recombinant retroviruses in the presence of stavudine (d4T). Cells which were infected despite the presence of d4T were isolated and subjected to infection with other retroviruses [replication-competent human immunodeficiency virus (HIV), replication-defective HIV or replication-defective recombinant murine retroviruses]. Each of the host cell types tested had a small subset of cells that were infected with HIV or murine retroviruses in the presence of d4T. Some of these infected cells could be infected repeatedly at high efficiency in the presence of d4T. This phenotype of 'persistent refractoriness' to the antiviral effects of d4T could be overcome by the addition of 5-fluoro-2-deoxyuridine (floxuridine) to d4T. The d4T-floxuridine combination also had potent antiretroviral effects in primary blood mononuclear cells.  (+info)

(8/314) Intracellular metabolism of CycloSaligenyl 3'-azido-2', 3'-dideoxythymidine monophosphate, a prodrug of 3'-azido-2', 3'-dideoxythymidine (zidovudine).

The administration of CycloSaligenyl 3'-azido-2',3'-dideoxythymidine monophosphate (CycloSal-AZTMP) to CEM cells resulted in a concentration- and time-dependent conversion to the 5'-monophosphate (AZTMP), 5'-diphosphate (AZTDP), and 5'-triphosphate (AZTTP) derivatives. High ratios of AZTMP/AZTTP were found in the CEM cell cultures treated with CycloSal-AZTMP. The intracellular T(1/2) of AZTTP in CEM cell cultures treated with either AZT and CycloSal-AZTMP was approximately 3 h. A variety of human T- and B-lymphocyte cell lines efficiently converted the prodrug to the AZT metabolites, whereas peripheral blood lymphocytes and primary monocyte/macrophages showed at least 10-fold lower metabolic conversion of the prodrug. CycloSal-AZTMP failed to generate marked levels of AZT metabolites in thymidine kinase-deficient CEM/TK(-) cells, an observation that is in agreement with the substantial loss of antiviral activity of CycloSal-AZTMP in CEM/TK(-) cells. The inability of CycloSal-AZTMP to generate AZTMP in CEM/TK(-) cells is presumably due to a relatively high hydrolysis rate of AZTMP to the parent nucleoside AZT, combined with the inability of CEM/TK(-) cells to phosphorylate AZT to AZTMP through the cytosolic salvage enzyme thymidine kinase.  (+info)