Efficacy and safety of stavudine and didanosine combination therapy in antiretroviral-experienced patients

Prenatal developmental toxicity evaluation of 2',3'-dideoxyinosine (ddI) and 2',3'-didehydro-3'-deoxythymidine (d4T) co-administered to Swiss Albino (CD-1) mice

BACKGROUND

In pregnant women, antiretroviral drugs improve maternal health and reduce vertical transmission of human immunodeficiency virus to the infant. However, few nonclinical studies have examined the potential for adverse drug interactions.

METHODS

On gestational days (GD) 6-16, mice were dosed with vehicle, ddI (360, 1440, or 2,880 mg/kg/day, p.o.), d4T (60, 240, or 480), or ddI/d4T combinations (360/60, 1,440/240, or 2,880/480). Daily doses were divided into two equal parts that were administered >or=6-hr apart. Body weight, clinical signs, and feed consumption were monitored. Pregnancies (22-24/group) were confirmed at necropsy. Maternal liver and gravid uterine weights (GUW), uterine implants (resorption, live or dead fetus), fetal body weight, gender, and morphologic anomalies (external, visceral, skeletal) were recorded.

RESULTS

Maternal body weight, clinical signs, and GUW were unaffected. Maternal weight change corrected for GUW was greater than controls at 60 and 480 d4T. Relative feed consumption during treatment was increased relative to controls at 1,440 and 2,880 ddI and 2,880/480 ddI/d4T. Relative maternal liver weight was elevated above controls at 240 and 480 d4T and 2,880/480 ddI/d4T, and above the constituent dose of ddI at 1,440/240 and 2,880/480 ddI/d4T. Liver weight was not affected by ddI and there was no significant drug interaction. Prenatal mortality and morphologic anomalies were not increased. Fetal body weight showed only a decreasing trend for ddI/d4T, no effect for ddI or d4T, and no statistically significant drug interaction.

CONCLUSIONS

In pregnant mice, ddI/d4T combinations were not associated with well-defined developmental toxicity or adverse drug interactions.

Long-term suppression of plasma viremia with highly active antiretroviral therapy despite virus evolution and very limited selection of drug-resistant genotypes

HIV-1 evolution and the possible emergence of mutations associated with resistance to antiretroviral inhibitors have been evaluated in a cohort of sixty-three patients successfully treated with highly active antiretroviral therapy (HAART). The patients under effective HAART were recruited in three different hospitals in Spain, and none of them had been treated (naïve) before entering this study. HIV-1 RNA levels, CD4+, and CD8+ T-cell counts were determined, and nucleotide sequences of proviral regions encoding protease and reverse transcriptase (RT) were obtained for longitudinal blood samples spanning a mean follow-up period of 88 weeks. Phylogenetic reconstructions and calculations of genetic distances among the different sequences of each patient were performed. All except one of the patients under study showed an early and sustained decrease in plasma HIV-1 RNA to levels that were below 200 copies/ml. The plasma viral decline paralleled a significant increase in the CD4+ T-lymphocyte counts. Amino acid sequence analyses revealed the occurrence of mutations associated with antiretroviral resistance in nine patients (14.3%) during HAART treatment, that in some cases could be attributed to excess G to A transitions. In six of the nine patients, the mutations conferred resistance to inhibitors administered in the treatment regime, although the mutations did not result in treatment failure. Sequence comparisons revealed viral evolution during the period of treatment in 47.5% of the patients. The results indicate successful suppression of HIV-1 under HAART for extended time periods, indistinguishable for patients in which evidence of virus evolution could or could not be documented.

Update on didanosine

Didanosine (ddl) has been a cornerstone of HIV management since it was made available in October 1991. Didanosine was originally introduced as an alternative to zidovudine (ZDV) for patients who were intolerant of ZDV or experienced disease progression during ZDV monotherapy. Didanosine is now used extensively as an integral component of multidrug combination regimens in both adults and children with HIV infection, and is now available for once-daily administration in the United States, Canada, and Europe. The recently approved Videx EC is an enteric-coated didanosine capsule dosed as one capsule, once daily. This paper provides an update of recently published studies on the use of ddl in combination anti-HIV therapy. In particular, these studies examine the rationale for the use of ddl as first-line anti-HIV therapy, and describe newer findings concerning its long-term efficacy, side effects, compliance, resistance, and once-daily use. The increased survival of HIV-infected patients is largely attributed to the introduction of the triple combination drug therapy but is probably also due to the long-term clinical efficacy of ddl.

Efficacy and safety of stavudine plus didanosine in asymptomatic HIV-infected children with plasma HIV RNA below 50,000 copies per milliliter

BACKGROUND

Simple antiretroviral drug combinations might provide a comparable benefit to standard triple regimens in patients with mild HIV disease, because poor adherence and toxicities often compromise the sustained benefit of the latest triple regimens, especially when protease inhibitors are used. Bad adherence is the main cause of virological failure in HIV-positive children. The activity and safety of a double combination of nucleosides with high genetic barrier for resistance (stavudine plus didanosine) was assessed in children with nonadvanced HIV disease.

METHOD

From February 1998 to March 1999, 16 children were enrolled in six Spanish hospitals in a trial in which didanosine (180 mg/m2/day) and stavudine (2 mg/Kg/day) were administered for 48 weeks to asymptomatic naive children with plasma HIV RNA below 50,000 copies/mL and CD4 counts above 15%. Genotypic resistance to nucleoside analogues was examined at baseline and at the end of the study.

RESULTS

At baseline, median age was 6.5 years (range, 2-14). The absolute and percentage mean CD4 counts were 864 and 32%, respectively (z score: -0.48 and -1.1). Mean plasma viral load was 4.05 log. No clinical events occurred during the 1-year study period. Minor side effects were recorded in two thirds of children, although none led to drug discontinuation. Lipoatrophy was not recognized in any of the participants. Plasma HIV RNA below 400 copies/mL was reached by 43% and 44% of patients at 24 and 48 weeks, respectively. The z score for absolute and percentage CD4 count increased significantly at 48 weeks (+0.63 and +0.97, respectively) in respect to baseline (p <.05). Resistance mutations linked to didanosine (L74V or M184V) or stavudine (V75T) were not recognized and neither were multinucleoside resistant genotypes (151 complex or 69 inserts). However, four children developed AZT-like mutations T215Y and/or M41L.

CONCLUSION

Treatment with a dual combination of didanosine plus stavudine in naive children with nonadvanced HIV disease is safe and provides a satisfactory virological outcome at 1 year. Toxicity and drug resistance seem to occur rarely when this combination is used, which allows good adherence and spares other future treatment options.

Peripheral neuropathy during stavudine-didanosine antiretroviral therapy

Peripheral neuropathy (PN) is among the most frequent side effects described with nucleoside reverse transcriptase inhibitors (NRTIs). We investigated the incidence, evolution and predictive factors of PN during stavudine (d4T)-didanosine (ddI) combination therapy in 65 HIV infected patients, previously treated with zidovudine and/or zalcitabine (ddC) for at least 3 months. A subset of 16 patients was referred for systematic electromyographic examination at weeks 0 and 24: six among the 16 exhibited nerve conduction abnormalities at day 0, probably related to previous ddC treatment in four of those and to HIV infection in the other two, with worsening of abnormalities in one patient at week 24. In total, seven of the 59 assessable patients (11.8%) exhibited grade 2-3 neuropathy, with a median time of occurrence of 17 weeks. Distal, symmetrical paraesthesias of the extremities were the first symptoms in all the patients; none had motor symptoms. In all the patients, PN resolved rapidly after stopping d4T. There were no statistically different parameters between the seven cases and the other 52 patients according to CD4 T cells, HIV RNA, Centers for Disease Control and Prevention (CDC) stage C or d4T daily dose. In our study, the d4T-ddI combination did not seem to increase the incidence of PN; risk factors for PN could not be identified, probably in part because of the low number of patients with PN.

Didanosine once daily: potential for expanded use

Factors affecting patient adherence to therapy, such as frequent daily dosing and complex dosing schedules, are widely understood to be key obstacles to the durability of effective anti-HIV therapy. Didanosine, a nucleoside analogue reverse transcriptase inhibitor (NRTI) that is a core component of combination antiretroviral regimens, is currently indicated for twice-daily dosing. However, the active metabolite of didanosine (2',3'-dideoxyadenosine-5'-triphosphate) has a long intracellular half-life that supports the use of didanosine in a more patient-friendly, once-daily dosing schedule. Clinical studies in which didanosine was administered either once or twice daily, as monotherapy or in combination with another NRTI, have demonstrated the equivalence of both dosing schedules, with respect to safety and tolerability, virologic and immunologic endpoints, and short-term clinical effects (e.g., weight gain). Preliminary results from recent studies support the clinical efficacy and utility of once-daily didanosine in combination antiretroviral regimens that provide maximal drug exposure, while allowing for once- or twice-daily dosing of all component drugs.

Long-term hydroxyurea in combination with didanosine and stavudine for the treatment of HIV-1 infection. Swiss HIV Cohort Study

OBJECTIVE AND METHODS

In 1998 we reported on a randomized comparison between stavudine plus didanosine plus placebo versus stavudine plus didanosine plus hydroxyurea (HU), in patients with a CD4 count of 200-500 x 10(6) cells/l. After 3 months, the HU group had a higher proportion of patients with viral load < 200 x 10 cells/l. At the end of the 3 months blinded period, patients in the placebo group had the option to add HU if their viral load remained > 200 x 10(6) cells/l. We report results after 24 months.

RESULTS

Seventy-two patients were randomized to the HU arm, and a further 30 elected to add HU after 12 weeks. Twenty-four months after the start of the trial, only 25% of the 72 patients originally randomized to HU, and 20% of the 30 who added HU after week 12, were still taking it. The reasons for stopping HU were: lack of efficacy (45%), adverse events (37%) and patient or physician preference (18%). Side effects were more frequent in the didanosine/stavudine/HU group than in the didanosine/stavudine group: neuropathy (35 versus 15%, P< 0.02), fatigue (22 versus 7%, P< 0.01), and nausea or vomiting (26 versus 9%, P< 0.01). Of those who had discontinued HU, 73% were taking three drugs including a protease inhibitor. Patients who had started HU were compared with similar patients who had started protease inhibitors in the Swiss cohort. The probability of stopping HU was higher than the probability of stopping nelfinavir or indinavir, and similar to the probability of stopping ritonavir.

CONCLUSION

HU increased the antiviral effect of stavudine plus didanosine. However, side effects were more frequent, and after 24 months the majority of patients had switched to protease inhibitor regimens.

A randomised, open-label comparison of three highly active antiretroviral therapy regimens including two nucleoside analogues and indinavir for previously untreated HIV-1 infection: the OzCombo1 study

BACKGROUND

Highly active antiretroviral therapy (HAART) including two nucleoside analogues and a potent protease inhibitor is standard of care initial therapy for HIV-infected adults. The best-tolerated and most potent initial HAART regimen is unknown and was investigated in this study.

METHODS

One hundred and nine HIV-infected adults with no prior antiretroviral therapy, and CD4 lymphocyte counts < 500 x 10(6) cells/l or plasma HIV RNA > 30,000 copies/ml were randomized to zidovudine-lamivudine-indinavir (ZDV-3TC-IDV), stavudine-lamivudine-indinavir (d4T-3TC-IDV) or stavudine-didanosine-indinavir (d4T-ddI-IDV) for 52 weeks. The primary endpoints were plasma HIV RNA and drug-related adverse events. Other assessments were overall safety, adherence and adverse events, CD4 lymphocyte counts, cutaneous delayed type hypersensitivity (DTH) responses and quality of life (Euroqol).

RESULTS

Only 58% patients had HIV RNA < 50 copies/ml plasma at 12 months, with no significant difference between the three regimes (P = 0.34). Drug-related adverse events sufficiently severe to warrant drug discontinuation were less common (P = 0.06) in patients receiving d4T-3TC-IDV (18%) than in those receiving ZDV-3TC-IDV (34%) or d4T-ddI-IDV (41%). The percentages of patients who remained on their assigned therapy with plasma HIV RNA < 50 copies/ml at 52 weeks were 60% with d4T-3TC-IDV, 53% with ZDV-3TC-IDV and 35% with d4T-ddI-IDV. Virological failure at 52 weeks was more likely in those whose adherence was estimated to be < 100% in the first 4 weeks of therapy (P = 0.02), but not in those who developed grade 3 or 4 drug-related adverse events. At 52 weeks, the mean CD4 lymphocyte count increase was 200 x 10(6) cells/l with only 7% of patients having counts lower than at baseline; DTH responses improved but remained clinically impaired in most patients. Quality of life improved significantly in all groups.

CONCLUSIONS

Initial HAART regimens including IDV failed to suppress plasma HIV RNA to < 50 copies/ml in > 40% patients after only 12 months of therapy although there was significant overall improvement immunologically and in quality of life. The type of dual nucleoside combination used was less important in predicting virological failure than was imperfect adherence early in therapy. Consideration should be given to modifying a HAART regimen relatively early in non-adherent patients.

The Virgo Study: Nevirapine, Didanosine and Stavudine Combination Therapy in Antiretroviral-Naive HIV-1-Infected Adults

The virological and immunological efficacy of the triple regimen containing nevirapine (once or twice daily), didanosine (once daily) and stavudine, in antiretroviral-naive patients infected with HIV-1, was evaluated in an open-label, prospective, non-randomized, multi-centre, 52-week study. The first 60 patients (VIRGO I) received nevirapine as the standard dose, 200 mg twice daily; the subsequent 40 patients (VIRGO II) received nevirapine at a dose of 400 mg once daily. All patients received 400 mg of didanosine once daily and 40 mg of stavudine twice daily, adjusted for body weight. At baseline, the median CD4 cell count and plasma viral load (pVL) were 414 cells/mm3 and 4.59 log10 copies/ml in VIRGO I, and 412 cells/mm3 and 4.87 log10 copies/ml in VIRGO II. Using an intent-to-treat, ‘non-completer equals failure’, analysis, 78% (95% CI, 68–88%) of patients in VIRGO I and 68% (95% CI, 53–83%) of those in VIRGO II had a pVL <500 copies/ml at 24 weeks; the proportions achieving a pVL of <50 copies/ml were 62% (95% CI, 50–74%) and 50% (95% CI, 35–65%), respectively. The week 24 median CD4 cell count increase was 168 cells/mm3 (VIRGO I) and 139 cells/mm3 (VIRGO II). At week 52, 39/45 (87%) of VIRGO I patients had pVL <500 copies/ml and 30/45 (67%) <50 copies/ml. Of the 100 patients, 44 experienced grade 2 to 4 adverse events; 20 permanently discontinued study medication because of an adverse event. Combination therapy with the three reverse transcriptase (RT) inhibitors stavudine, once-daily didanosine and either once- or twice-daily nevirapine could be considered as an alternative option for first-line antiretroviral therapy.

Incidence of neuropathy in HIV-infected patients on monotherapy versus those on combination therapy with didanosine, stavudine and hydroxyurea

BACKGROUND

Sensory neuropathy is a common adverse effect of the nucleoside analogue anti-retroviral drugs didanosine (ddl) and stauvudine (d4T). These drugs are increasingly being used in combination, and it is not currently known whether the incidence of neuropathy is higher with combination compared to individual drug use. It is also not known if hydroxyurea, used to potentiate the antiviral efficacy of these drugs, may also increase the risk of neuropathy. The purpose of this analysis is to investigate if the combination of ddl and d4T, with or without hydroxyurea, has a higher incidence of neuropathy than a single drug regimen.

METHODS

Data were obtained from patients followed longitudinally by the Johns Hopkins AIDS Services. Incidence rates of development of neuropathy were calculated for each of five regimens: ddl (+/- hydroxyurea), ddl + d4T (+/- hydroxyurea), and d4T. Cox proportional hazard regression was used to compare the relative risk of neuropathy for each regimen adjusting for CD4 cell count, other drugs received, and time on therapy.

RESULTS

A total of 1116 patients received at least one of the five regimens. There were 117 cases of neuropathy. The crude incidence rate of neuropathy ranged from 6.8 cases per 100 person-years for ddl to 28.6 cases per 100 person-years for ddl + d4T + hydroxyurea. Compared with ddl alone, and adjusting for CD4 cell counts and other variables, the relative risk of neuropathy was 1.39 [95% confidence interval (CI): 0.84-2.32] for d4T alone, 2.35 (95% CI: 0.69-8.07) for ddl + hydroxyurea, 3.50 (95% CI: 1.81-6.77) for ddl + d4T, and 7.80 (95% CI: 3.92-15.5) for ddl + d4T + hydroxyurea.

CONCLUSIONS

Based on the data, the risk of neuropathy is additive or even synergistic for ddl + d4T + hydroxyurea compared with ddl or d4T alone. The combination of ddl + d4T also increases the risk of neuropathy but less than when hydroxyurea is included.

Natural history of serum HIV-1 RNA levels in 330 patients with a known date of infection. The SEROCO Study Group

OBJECTIVE

To describe the spontaneous course, before the introduction of highly active antiretroviral therapy (HAART), of HIV-1 RNA during the AIDS-free period of the disease. To assess the predictive value of changes in HIV-1 RNA levels.

DESIGN

A total of 330 patients with a known date of infection followed in the SEROCO cohort.

METHODS

HIV-1 RNA levels (threshold, 200 copies/ml) were evaluated from 2243 frozen sera obtained from enrolment until the onset of AIDS or until February 1996. Lowess curves were used to describe the variations of viraemia during follow-up. A Cox regression model was used to assess the predictive value of early and updated CD4 cell count and viral load.

RESULTS

In addition to a lower early viral load, patients who remained AIDS-free had, on average, a longer period of viral load decrease after infection (36 versus 18 months), followed by a slower viral load increase compared with those who progressed to AIDS. A true plateau-phase after the seroconversion period, lasting approximately 4 years, was identified only in patients who remained AIDS-free for at least 90 months. In multivariate analysis, both early viral load and later changes were significant predictors of progression to AIDS. A decrease in the CD4 cell count to less than 200 cells/microl and the onset of a group B condition remained significant predictors of progression.

CONCLUSION

Our study extends to the early post-seroconversion phase the prognostic value of extracellular HIV-1 RNA levels. Moreover, our data suggest that, in most HIV-infected individuals, a progressive loss of control of viral replication arises during the early years of HIV-1 infection.

Didanosine: an updated review of its use in HIV infection

Didanosine, like zidovudine, stavudine and lamivudine, is a nucleoside analogue reverse transcriptase inhibitor (NRTI). In the target cell for HIV, didanosine is converted to its active moiety, dideoxyadenosine-5'-triphosphate (ddATP), which inhibits HIV reverse transcriptase and terminates viral DNA growth. It is now well established that didanosine therapy produces beneficial effects on virological and immunological markers of HIV disease and improves clinical outcome in adults or children with HIV infection. In numerous clinical trials, pronounced and sustained decreases in plasma HIV RNA levels and increases in CD4+ cell counts occurred in previously untreated or antiretroviral therapy-experienced patients treated with didanosine in combination with at least 1 other antiretroviral drug; zidovudine, stavudine, lamivudine, nevirapine, nelfinavir and hydroxyurea (hydroxycarbamide) are among the drugs that have been given in combination with didanosine. Of note, HIV RNA levels decreased to below the limits of detection in some patients receiving triple or dual therapy with didanosine-containing regimens. In double-blind, placebo-controlled trials, triple therapy with didanosine, zidovudine and nevirapine was significantly more effective than dual therapy with various combinations of these agents in improving surrogate disease markers in treatment-naive patients and in delaying disease progression or death in treatment-experienced patients with advanced disease. Improvements in virological and immunological markers were greater with didanosine-containing triple regimens than with dual therapy or monotherapy in comparative trials. Triple therapy with didanosine, stavudine and indinavir showed efficacy similar to that of various other triple therapy regimens in nonblind comparative trials. Comparator regimens included combinations of stavudine, lamivudine plus indinavir, zidovudine, lamivudine plus indinavir and didanosine, stavudine and nevirapine. Combination therapy with didanosine plus hydroxyurea as dual therapy or with a third agent produced marked and sustained decreases in HIV RNA levels in the plasma and in lymph nodes. Combination therapy with didanosine and zidovudine delays disease progression and prolongs survival in patients with intermediate or advanced HIV infection. In large, randomised, double-blind, clinical trials, dual therapy with didanosine plus zidovudine was significantly more effective than zidovudine monotherapy in preventing disease progression and prolonging survival in previously untreated or antiretroviral therapy-experienced patients with intermediate or advanced HIV infection. Pancreatitis and peripheral neuropathy are serious adverse effects of didanosine. These effects are dose-related and usually reversible after discontinuation of treatment. Nausea, vomiting, diarrhoea and/or abdominal pain have been reported in patients receiving treatment with the drug.

CONCLUSIONS

Didanosine is an effective and generally well tolerated drug in previously untreated and antiretroviral therapy-experienced patients with HIV infection. Given once or twice daily, it has an important role as a component of triple combination regimens for the treatment of patients with symptomatic or asymptomatic HIV infection.

Safety and antiretroviral effects of combined didanosine and stavudine therapy in HIV-infected individuals with CD4 counts of 200 to 500 cells/mm3

The safety and antiretroviral effects of didanosine and stavudine in combination were evaluated in 86 people infected with HIV with CD4 counts between 200 and 500 cells/mm3 who had received <7 days of prior nucleoside analogue antiretroviral treatment. Patients were randomized to receive blinded treatments with one of five weight-adjusted, twice-daily regimens of didanosine and stavudine (100 + 10 mg, 100 + 20 mg, 100 + 40 mg, 200 + 20 mg, and 200 + 40 mg) for up to 1 year. Dosages were adjusted appropriately for patients weighing <60 kg and reduced in response to adverse effects. No clear dose-related differences among treatment groups were detected with regard to suppression of plasma HIV RNA level or reduction in infectious titers in peripheral blood mononuclear cells (PBMCs), improvement in CD4 count, or adverse effects. However, trends toward greater decreases in viral load and increases in CD4 count were detected when treatment groups containing the full recommended dosage of one or both agents (high-dose subgroup; arms 3, 4, and 5) were compared with the groups receiving lower dosages. At 28 weeks the mean log 10 HIV RNA decrease was 1.12 (n = 52) and at 52 weeks it was 0.97 (n = 32). Combination therapy was well tolerated, with no apparent dose-related adverse effects. Peripheral neuropathy occurred in 2 of 86 (2.3%) of patients. Didanosine and stavudine together appear to be a good nucleoside analogue foundation for aggressive triple- or quadruple-drug therapy. Full therapeutic doses of each of these two agents should be used to achieve optimal suppression of HIV replication.

Highly active antiretroviral therapy (HAART) for the treatment of infection with human immunodeficiency virus type 1

Highly active antiretroviral therapy (HAART) refers to a broad category of treatment regimens usually comprised of three or more antiretroviral drugs that, in previously untreated HIV-1-infected patients, are expected to reduce plasma virus levels below the limits of detection. Most HAART regimens include drugs from at least two of the three classes of antiretroviral therapy (nucleoside analog reverse transcriptase (RT) inhibitors, non-nucleoside analog RT inhibitors, and protease inhibitors). In deciding when to initiate antiretroviral therapy, physicians and their patients must balance the virological and immunological benefits of early treatment with the costs of drug therapy, the risk of drug side effects, and the risk of drug resistance if adherence is suboptimal. In previously untreated patients, HIV-1 replication can be suppressed indefinitely with certain HAART regimens. In previously treated patients, the benefits of HAART are often significantly diminished.