Stavudine: a review of its pharmacodynamic and pharmacokinetic properties and clinical potential in HIV infection

Stavudine is a nucleoside analogue which undergoes intracellular phosphorylation to its active metabolite, stavudine-5'-triphosphate. At clinically relevant concentrations, the active metabolite restricts HIV replication by inhibiting the inclusion of thymidine-5'-triphosphate into proviral DNA by HIV reverse transcriptase, and/or by causing DNA chain termination. Viral resistance to stavudine does not commonly develop during treatment. Where it has developed, up to a 12-fold increase in resistance has been observed in clinical isolates from patients treated with stavudine for long periods. Stavudine 40mg twice daily and zidovudine 200mg 3 times daily were compared in 822 patients at various stages of HIV infection who had previously received long term zidovudine therapy. Stavudine was superior for both primary and surrogate end-points including clinical progression, treatment failure, increase in CD4+ cell counts and bodyweight gain. In a larger study, stavudine 40mg twice daily provided greater benefit than stavudine 20mg twice daily in terms of weight gain, haematological findings and the number of hospitalisations in 11 784 patients intolerant of or resistant to, zidovudine and didanosine. Peripheral neuropathy is the major dose-limiting adverse event associated with stavudine therapy and occurred more frequently with stavudine than zidovudine. However, haematological adverse events were observed less frequently with stavudine than with zidovudine. Thus, stavudine is effective in alleviating signs and symptoms of HIV infection in patients intolerant of or no longer responding to, zidovudine or didanosine. It is also more effective than zidovudine in slowing disease progression in patients previously treated with zidovudine for long periods. The results of studies which will reveal the role of stavudine therapy in untreated patients and in combination with other anti-HIV agents are awaited with interest.

Effect of stavudine on human immunodeficiency virus type 1 virus load as measured by quantitative mononuclear cell culture, plasma RNA, and immune complex-dissociated antigenemia

The antiviral effect of stavudine (2', 3'-didehydro-3'-deoxythymidine) against human immunodeficiency virus (HIV) type 1 was measured in 15 HIV-infected patients at baseline and at weeks 4, 10, 22, 34, and 52 of therapy. Patients received 0.1, 0.5, 1.0, or 2.0 mg/kg/day of stavudine. At all time points examined during the 52 weeks of therapy, the median virus titers in peripheral blood mononuclear cells were decreased 1-2 logs, and median immune complex-dissociated antigen levels were reduced 37%-67% compared with baseline values. Plasma RNA content measured by polymerase chain reaction was reduced approximately 0.5 log from baseline median values at both time points examined (weeks 10 and 52). These data demonstrate that stavudine has a substantial and durable antiviral effect.

Pharmacokinetics of stavudine (2',3'-didehydro-3'-deoxythymidine) in the neonatal macaque (Macaca nemestrina)

Our objective was to determine whether age effects the pharmacokinetics of stavudine (2',3'-didehydro-3'-deoxythymidine) in the neonatal pig-tailed macaque (Macaca nemestrina). The drug (5 mg/kg of body weight) was administered serially as a single intravenous bolus to the same four macaques at the ages of < 1 week, 1 month, and 4 months. Plasma clearance at < 1 week of age was significantly lower (P < 0.05) than the corresponding values at 1 month and 4 months. Our data indicate that the pharmacokinetics of stavudine change significantly with age in M. nemestrina.

A phase I/II evaluation of stavudine (d4T) in children with human immunodeficiency virus infection

OBJECTIVES

To determine the pharmacokinetic properties, tolerance, safety, and preliminary activity of stavudine in human immunodeficiency virus (HIV)-infected children.

DESIGN

Phase I/II, open and dose-ranging (0.125 to 4 mg/kg/day in two divided doses).

PATIENTS

Thirty-seven HIV-infected children (median age, 5.5 years; range, 7 months to 15 years) with a median CD4+ lymphocyte count at baseline of 242 cells/microL (range 2 to 2290 cells/microL). Thirty children had symptomatic HIV disease at entry; seven had HIV-related immunosuppression alone. Twenty-nine subjects had a history of prior zidovudine (ZDV) therapy.

RESULTS

As compared with adults receiving the same weight-adjusted doses, the children we studied had lower maximum observed stavudine plasma concentrations (CMAX) and area under the plasma concentration versus time curves (AUC), and more rapid stavudine elimination. The absolute oral bioavailability of the drug ranged from 61% to 78%. There was no plasma accumulation of the drug between day 1 and week 12. Week 12 cerebrospinal fluid stavudine concentrations in seven subjects, obtained approximately 2 to 3 hours after oral doses, ranged from 16% to 97% of concomitant plasma concentrations. Stavudine was well-tolerated and there were no dose-related clinical or laboratory adverse events. One subject with baseline neurologic abnormalities experienced a transient episode of apparent pain or discomfort in her fingers, possibly related to stavudine. All other adverse events were attributed to underlying disease. Stavudine activity, measured indirectly by CD4+ lymphocyte count and serum p24 antigen concentration changes, was observed in some subjects. Progression of HIV disease and survival correlated with prior ZDV therapy, HIV disease classification, baseline CD4+ lymphocyte count, and weight growth velocity.

CONCLUSIONS

Stavudine appears to hold promise for the treatment of HIV infection in children. Its pharmacokinetic properties are consistent and predictable, and it appears to be remarkably well-tolerated and safe. Although our study was not designed to assess the drug's efficacy, preliminary clinical and laboratory evidence of activity was observed.

Dose-related activity of stavudine in patients infected with human immunodeficiency virus

In a multicenter, randomized, open-label, dose-ranging study to determine the relative effects of three dose levels of stavudine on CD4 lymphocyte count, weight gain, and hematologic variables in patients infected with human immunodeficiency virus (HIV), 152 patients with CD4 lymphocyte counts < or = 600/mm3 received stavudine at 0.1 mg/kg/day (n = 51), 0.5 mg/kg/day (n = 53), or 2.0 mg/kg/day (n = 48). The study was designed to evaluate the activity of stavudine after 10 weeks of therapy and permitted extended dosing and follow-up for long-term safety. A significant dose effect on increases in CD4 lymphocyte counts and declines in HIV titer in peripheral blood mononuclear cells was observed. Stavudine was well-tolerated; the only dose-related, dose-limiting adverse event was peripheral neuropathy, which usually was reversible. In this trial, the most favorable therapeutic index was seen at 0.5 mg/kg/day.

Biologic effects and safety of stavudine: overview of phase I and II clinical trials

Data on the biologic effects and safety of stavudine in patients with AIDS and AIDS-related complex represent results of two phase I trials (n = 84), another phase I study of patients with hematologic intolerance to zidovudine (n = 23), and a phase II trial (n = 152). The daily doses of stavudine ranged from 0.1 to 12.0 mg/kg. Increases in CD4 cell count, declines in serum p24 antigen, and weight gain were all related to the dose of stavudine. Doses of < or = 2 mg/kg/day (n = 216) were well-tolerated, with a median duration of therapy of > or = 48 weeks in the phase I studies and > or = 79 weeks in the phase II study. The predominant dose-limiting toxicity was peripheral neuropathy, which was related to both the dose and duration of treatment with stavudine. Elevations of liver enzymes were seen in some patients but appeared to be related to underlying disease rather than treatment. There was no evidence of dose-related hematologic toxicity.

Dose proportionality of stavudine in HIV seropositive asymptomatic subjects: application to bioequivalence assessment of various capsule formulations

The dose proportionality and bioequivalence of the capsule formulations used in clinical trials and the proposed commercial formulations of stavudine were assessed in an open-label, single-dose, randomized four-way crossover study in 16 asymptomatic HIV-infected males. One capsule of stavudine (5, 10, 20, or 40 mg) was administered orally to each subject in each of the four treatment periods. Serial blood samples were collected for 10 h after each dose and the plasma was assayed for intact stavudine by a validated radioimmunoassay method. The plasma concentration-time data were subjected to non-compartmental pharmacokinetic analysis. For doses ranging from 5 to 40 mg, mean Cmax and AUC0-infinity values were in the range of 110.36-889.34 ng mL-1 and 246.46-1945.97 h ng mL-1 respectively. The mean Cmax and AUC0-infinity of stavudine increased in a dose-proportional manner. Irrespective of the dose, mean Cmax values were observed at a median tmax of 0.75 h or less. Mean t1/2 values were 1.97, 1.77, 1.67 and 1.66 h for the 5, 10, 20, and 40 mg capsules, respectively. For bioequivalence assessment, Cmax and AUC0-infinity values were normalized to the 10 mg dose since these parameters were dose proportional. The 10 mg capsule formulation used in phase-3 clinical trials was chosen as the reference. The relative bioavailability estimates and 90% confidence limits for the dose-normalized Cmax values with the 10 mg capsule as the reference were 86% (76%, 96%), 99% (88%, 110%), and 90% (80%, 100%) for the 5, 20, and 40 mg capsules, respectively. The differences in the point estimates of the dose-normalized AUC0-infinity values for the 5, 20, and 40 mg capsules relative to the 10 mg phase-3 capsule were 1% or less, and the 90% confidence limits were all within 95-106%. These results indicate that stavudine exhibits linear pharmacokinetics and that the 5, 10, 20, and 40 mg capsules of stavudine are bioequivalent.

Design and implementation of the stavudine parallel-track program

In a randomized, double-blind, large, simple trial, the safety and efficacy of two weight-adjusted dose levels of stavudine were evaluated in patients with advanced human immunodeficiency virus (HIV) infection. All patients were refractory to or intolerant of both zidovudine and didanosine. Patients weighing > or = 60 kg received 20 or 40 mg of stavudine twice daily. The dose was reduced to 15 or 30 mg for patients weighing 40-59 kg and to 10 or 20 mg for those weighing < 40 kg. The primary efficacy end points were survival and time to clinical progression of HIV disease. The primary safety end point was time to dose-limiting neuropathy. A total of 8127 patients were enrolled as of 31 July 1993. Although many patients who might have benefitted from stavudine were reached by the parallel-track program, a review of demographic data revealed disproportionate representation by white men from large metropolitan areas on both coasts.

Effect of the combination of interferon-alpha and stavudine on Friend virus infections in (B10.A x A.By)F1 mice

The anti-Friend leukemia virus (FLV) effects of interferon-alpha-A/D (IFN-alpha) and 2',3'-didehydro-2',3'-dideoxythymidine (stavudine) used alone and in combination were examined in Mus dunni cells using a checkerboard-type experiment design. Strong antiviral synergy and a suggested cytotoxic synergy were seen. In two experiments to evaluate the effect of combining therapy with IFN-alpha and stavudine against FLV disease in the hybrid mouse strain (B10.A x A.By)F1, which is a strong producer of cytotoxic T cells, the drug combination resulted in better inhibition of FLV disease than did either drug used alone. Combination therapy inhibited splenomegaly, splenic virus infectious centers, plasma virus, and the virus-induced increase in hematocrit to a greater degree than did either drug alone. These data indicate that combination therapy with stavudine and IFN-alpha is effective in the treatment of murine retrovirus infections and may be of value in the treatment of human AIDS.