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

Reductions in Stavudine Dose Might Ameliorate Mitochondrial-Associated Complications Without Compromising Antiviral Activity

BACKGROUND

Stavudine (d4T) is a nucleoside analogue approved for the treatment of HIV infection. Concern has risen due to its association with mitochondrial toxicity. Given that the toxicity might be dose-dependent, we explored prospectively whether lowering d4T doses might improve the safety profile of the drug without compromising its antiviral activity.

METHOD

All HIV-infected patients seen at our institution during the first semester of year 2003 who were receiving a d4T-containing regimen and had plasma HIV RNA below 50 copies/mL for the previous 3 months were invited to participate in a trial in which half of patients reduced the dose of d4T from 40 to 30 mg bid (cases) and the other half continued with the same d4T dose (controls).

RESULTS

A total of 92 patients were recruited in the study: 47 cases and 45 controls. A total of 9 patients experienced virological failure during the following 12 months: 4 cases and 5 controls. No significant differences between groups were recognized for mean transaminase levels, cholesterol, triglycerides, and lactate at baseline nor over the 12-month follow-up period. Lipodystrophy was recognized in 20% of patients at baseline, without significant differences between groups, and no significant improvements were recognized in the d4T 30 mg bid arm after 12 months follow-up. However, a median significant increase of 2.23-fold in the mitochondrial DNA content in peripheral blood mononuclear cells (PBMCs) was recognized in a subset of 11 patients who reduced the d4T dose, whereas it remained unchanged in 10 controls.

CONCLUSION

A reduction in the d4T dose from 40 to 30 mg bid may ameliorate mtDNA depletion in PBMCs without compromising the antiviral activity of the drug. However, significant improvements on surrogate laboratory markers of mitochondrial toxicity or in lipoatrophy could not be recognized over 12 months follow-up.

Low dose versus high dose stavudine for treating people with HIV infection

BACKGROUND

Stavudine remains a component of combination antiretroviral therapy (ART) in resource-constrained countries due to its relatively low cost despite the WHO recommendation for its phasing out as a strategy to reduce stavudine associated toxicities. Where stavudine is still in use, it is recommended at a dose lower than the standard dose in order to reduce stavudine related toxicity.

OBJECTIVES

To compare the safety and virologic efficacy of low dose versus high dose stavudine for treating HIV-1 infection.

SEARCH METHODS

The comprehensive search strategy developed by the Cochrane HIV/AIDS Review Group was used to identify randomised controlled trials that compared the use of low dose versus high dose stavudine. The last search was conducted in February 2014 and the searches covered the period 1996 to 2014.

SELECTION CRITERIA

Randomised controlled trials comparing the use of low dose and high dose stavudine as part of ART combination therapy for treating adults.

DATA COLLECTION AND ANALYSIS

Two reviewers independently selected eligible trials, assessed methodological quality of the included studies and completed data extraction and analysis.

MAIN RESULTS

The search identified 3952 abstracts which were scanned for relevance. Three trials met the inclusion criteria (Milinkovic 2007; McComsey 2008; Sanchez-Conde 2005). All three trials were conducted in developed countries, participants were ART experienced and all had sustained virologic suppression at baseline. A total of 157 participants were recruited to the trials. Sample sizes ranged from 24 to 92 and more than 79% of participants were male.The studies were at a high risk of selection, performance/detection and selective outcome reporting biases. Some baseline characteristics differed among the groups, including triglyceride levels in two studies and body mass index in one study. In light of variation in the design and follow-up of the study results, no meta-analysis was performed and the results of single studies are presented. There was no significant difference in virologic suppression in the included studies (Milinkovic 2007; McComsey 2008; Sanchez-Conde 2005); Risk Ratio (RR) 1.09 (95% CI: 0.93 to 1.28), 0.94 (95% CI:0.59 to 1.50) and 1.03 (95% CI: 0.90 to 1.18) respectively. Symptomatic hyperlactatemia was seen in the high dose arm of the Milinkovic 2007 study; RR 0.21 (95% CI: 0.01 to 4.66), in no participants in the McComsey 2008 trial and not reported on in the Sanchez-Conde 2005 trial. McComsey 2008 and Milinkovic 2007 demonstrated a reduction in bone mineral density (BMD), reduction in limb fat and an increase in triglycerides in the high dose arms. The studies did not indicate that any participants discontinued treatment due to adverse events.

AUTHORS' CONCLUSIONS

This systematic review identified only three small trials that evaluated virologic efficacy and safety of high dose versus low dose stavudine. All three trials were conducted in developed countries and none reported from developing countries yet stavudine remains a component of ART combination therapy in many developing countries. It was not possible to perform a meta-analysis on these trails. Individual results from the trials were imprecise and have not identified a clear advantage in virologic efficacy or safety between low and high dose stavudine. Furthermore, enrolled participants were treatment experienced with sustained virologic suppression and so existing data cannot be generalized to settings where stavudine is currently used in ART naive patients with high viral loads. Stavudine dose reduction trials in ART naive patients, in developing countries where stavudine is still being used are warranted as the phasing out of stavudine that is recommended by WHO may not be immediately universally feasible.

Synthesis and antiviral evaluation of 2-amino-6-carbamoylpurine dioxolane nucleoside derivatives and their phosphoramidates prodrugs

The synthesis of 9-(β-d-1,3-dioxolan-4-yl)2,6-diaminopurine nucleoside phosphoramidate prodrugs as well as various 2-amino-6-carbamoylpurine dioxolane derivatives and their phosphoramidates prodrugs is reported. Their ability to block HIV and HBV replication along with their cytotoxicity toward HepG2, human lymphocyte, CEM and Vero cells was also assessed.

Estimation of intracellular concentration of stavudine triphosphate in HIV-infected children given a reduced dose of 0.5 milligrams per kilogram twice daily

The antiviral efficacy of stavudine depends on the trough concentration of its intracellular metabolite, stavudine-triphosphate (d4T-TP), while the degree of stavudine's mitochondrial toxicity depends on its peak concentration. Rates of mitochondrial toxicity are high when stavudine is used at the current standard pediatric dose (1 mg/kg twice daily [BID]). Evidence from adult work suggests that half of the original standard adult dose (i.e., 20 mg BID) may be equally effective, with markedly less mitochondrial toxicity. We present a population pharmacokinetic model to predict intracellular d4T-TP concentrations in pediatric HIV-infected patients administered a dose of 0.5 mg/kg BID. Our model predicted that the reduced pediatric dose would result in a trough intracellular d4T-TP concentration above that of the reduced 20-mg adult dose and a peak concentration below that of the 20-mg adult dose. The simulated pediatric intracellular d4T-TP at 0.5 mg/kg BID resulted in median peak and trough values of approximately 23.9 fmol/10(6) cells (95% prediction interval [PI], 14.2 to 41 fmol/10(6) cells) and 14.8 fmol/10(6) cells (95% PI, 7.2 to 31 fmol/10(6) cells), respectively. The peak and trough concentrations resulting from a 20-mg BID adult dose were 28.4 fmol/10(6) cells (95% PI, 17.3 to 45.5 fmol/10(6) cells) and 13 fmol/10(6) cells (95% PI, 6.8 to 28.6 fmol/10(6) cells), respectively. Halving the current standard pediatric dose should therefore not compromise antiviral efficacy, while markedly reducing mitochondrial toxicity.

Increases in regimen durability associated with the introduction of tenofovir at a large public-sector clinic in Johannesburg, South Africa

INTRODUCTION

In April 2010, tenofovir replaced stavudine in public-sector first-line antiretroviral therapy (ART) in South Africa. The association of tenofovir with fewer side effects and toxicities compared to stavudine could translate to increased durability of tenofovir-based regimens. We evaluated changes over time in regimen durability at the Themba Lethu Clinic, Johannesburg, South Africa.

METHODS

This was a cohort analysis of treatment-naïve, non-pregnant adult patients initiated on ART between April 2004 and December 2011. First-line ART regimens before April 2010 consisted of stavudine or zidovudine with lamivudine and either efavirenz or nevirapine. Tenofovir was substituted for stavudine after April 2010. We evaluated the frequency and type of single-drug substitutions (excluding switches to second-line therapy). Cox models were used to evaluate the association of ART initiation year and antiretroviral drug type with single-drug substitutions in the first 12 months on treatment.

RESULTS

One thousand nine hundred and sixty-four (10%) substitutions occurred amongst 19,699 patients. Excluding 2004 (year of treatment roll-out), before 2010 one-year single-drug substitutions ranged from 10.0 to 13.1%. In 2011, well after integration of tenofovir, substitutions decreased to 5.6%. Single-drug substitution was lowest amongst patients on tenofovir (5.1%) versus zidovudine (11.3%), 30 mg stavudine (10.5%) or 40 mg stavudine (14.4%). Adjusted Cox models showed that patients initiating treatment between 2005 and 2010 (vs. 2011) had a twofold increased hazard of single-drug substitution, while those on zidovudine or stavudine had a two to threefold increase in single-drug substitution versus tenofovir patients in the first 12 months on ART.

CONCLUSIONS

The decline in single-drug substitutions is associated with the introduction of tenofovir. Tenofovir use could improve regimen durability and treatment outcomes in resource-limited settings.

Adenosine Dioxolane Nucleoside Phosphoramidates as Antiviral Agents for Human Immunodeficiency and Hepatitis B Viruses

There are currently six nucleoside reverse transcriptase inhibitors (NRTI) that are FDA approved for human clinical use and these remain the backbone of current HIV therapy. In order for these NRTIs to be effective they need to be phosphorylated consecutively by cellular kinases to their triphosphate forms. Herein, we report the synthesis of C-6 modified (-)-β-D-(2R,4R)-1,3-dioxolane adenosine nucleosides and their nucleotides including our novel phosphoramidate prodrug technology. We have introduced a side chain moiety on the phenol portion of the phosphoramidate to reduce the toxicity potential. The synthesized phosphoramidates displayed up to a 3,600-fold greater potency versus HIV-1 when compared to their corresponding parent nucleoside and were up to 300-fold more potent versus HBV. No cytotoxicity was observed up to 100 μM in the various cell systems tested, except for compound 17 and 18 which displayed a CC₅₀ of 7.3 and 12 μM respectively in Huh-7 cells. The improved and significant dual antiviral activity of these novel phosphoramidate nucleosides was partially explained by the increased intracellular formation of the adenosine dioxolane triphosphate.

Phosphoramidate prodrugs of (-)-β-D-(2R,4R)-dioxolane-thymine (DOT) as potent anti-HIV agents

BACKGROUND

Nucleoside reverse transcriptase inhibitors (NRTIs) are an effective class of agents that has played a vital role in the treatment of HIV infections. (-)-β-D-(2R,4R)-dioxolane-thymine (DOT) is a thymidine analogue that is active against wild-type and NRTI-resistant HIV-1 mutants. It has been shown that the anti-HIV activity of DOT is limited due to poor monophosphorylation.

METHODS

To further enhance the anti-HIV activity of DOT, an extensive structure-activity relationship analysis of phosphoramidate prodrugs of DOT monophosphate was undertaken. These prodrugs were evaluated for anti-HIV activity using Hela CD4 β-gal reporter cells (P4-CCR5 luc cells).

RESULTS

Among the synthesized prodrugs, the 4-bromophenyl benzyloxy l-alanyl phosphate derivative of DOT was the most potent, with a 50% effective concentration of 0.089 μM corresponding to a 75-fold increase in activity relative to the parent nucleoside DOT with no increased cytotoxicity. The metabolic stability of a selected number of potent DOT phosphoramidates was also evaluated in simulated gastric fluid, simulated intestinal fluid, human plasma and liver S9 fractions.

CONCLUSIONS

A series of new phosphoramidate prodrugs of DOT were prepared and evaluated as inhibitors of HIV replication in vitro. Metabolic stability studies indicated that these DOT phosphoramidate derivatives have the potential to show acceptable stability in the gastrointestinal tract, but they metabolize rapidly in the liver.

Toxicity associated with stavudine dose reduction from 40 to 30 mg in first-line antiretroviral therapy

Background

To compare the incidence and timing of toxicity associated with the use of a reduced dose of stavudine from 40 to 30 mg in first-line antiretroviral therapy (ART) for HIV treatment and to investigate associated risk factors.

Methods

Multicohort study including 23 HIV programs in resource-limited countries. Adults enrolled between January 2005 and December 2009. Four-year rates of all-cause and stavudine-specific toxicity were estimated. Multilevel mixed-effect Poisson and accelerated failure models were used to investigate factors associated with toxicity and timing of diagnosis.

Findings

A total of 48,785 patients contributed 62,505 person-years of follow-up. Rate of all-cause toxicity was 7.80 (95%CI 7.59–8.03) per 100 person-years, but varied greatly across sites (range 0.41–21.76). Patients treated with stavudine 40 mg had higher rates of toxicity (adjusted rate ratio [aRR] 1.18, 95%CI 1.06–1.30 during the first year of ART; and 1.51, 95%CI 1.32–1.71 during the second year). Women, older age, initial advanced clinical stage, and low CD4 count were associated with increased toxicity rate ratios. Timing of lipodystrophy and peripheral neuropathy diagnosis were 12% and 13% shorter, respectively, in patients treated with stavudine 40 mg than in those receiving 30 mg stavudine dose (P = 0.03 and 0.07, respectively).

Insterpretation

Higher rates of drug-related toxicity were reported in patients receiving stavudine 40 mg compared with 30 mg, and the time to toxicity diagnosis was shorter in patients treated with the higher dose. Higher rates of toxicity were observed during the first two years of ART.

d4T: keep it or abandon it?

Stavudine is a nucleoside analogue used widely for first-line treatment of HIV in developing and middleincome countries. The World Health Organization recommended that all patients should switch to stavudine (30mg BID). However, there is evidence from the dose-ranging trials that patients with body weight below 60kg should use a dose of 20mg BID. For patients who show adverse events on stavudine, a switch to other nucleoside analogues can be considered. This article reviews d4T to study if it should be kept or abandoned.

Early nucleoside reverse transcriptase inhibitors for the treatment of HIV: a brief history of stavudine (D4T) and its comparison with other dideoxynucleosides

The occasion of this 25th anniversary issue encouraged us to reminisce about the important history of the discovery of the dideoxynucleoside analogues for the treatment of HIV/AIDS and to chronicle our thoughts about a particular exciting and rewarding period of our scientific careers. Following the identification of the anti-HIV activity of zidovudine (AZT), we participated in the urgent quest to discover optimal treatments of HIV infection and AIDS. A number of previously synthesized nucleoside analogues were comparatively evaluated, and stavudine (D4T) emerged as a promising candidate for development. Following clinical evaluation, D4T became a mainstay of the initial antiretroviral combination therapy, prolonging and saving numerous lives. It has only recently been supplanted by better-tolerated treatments. This article forms part of a special issue of Antiviral Research marking the 25th anniversary of antiretroviral drug discovery and development, vol. 85, issue 1, 2010.

HIV suppression with stavudine 30 mg versus 40 mg in adults over 60 kg on antiretroviral therapy in South Africa

In 2007, the WHO recommended a maximum stavudine dose of 30 mg. We compared virologic suppression among patients weighing more than 60 kg and receiving stavudine 30 mg (n = 110) versus 40 mg (n = 508) in community HIV clinics in South Africa, before and after guidelines changed. At 6 months, HIV RNA less than 400 copies/ml was achieved in 79% and 81% receiving 30 and 40 mg stavudine, respectively (chi2, P = 0.6). In regression modeling, including baseline HIV RNA and nonnucleoside reverse transcriptase inhibitor agent, stavudine dose remained unassociated with suppression.

Safety of stavudine in the treatment of HIV infection with a special focus on resource-limited settings

BACKGROUND

Western randomized trials and prospective cohorts in resource-limited settings have proven virological success with stavudine-based highly active antiretroviral therapy. However, stavudine is no longer recommended in first-line treatments in these two settings due to its intrinsic toxicities and side effects. Yet it remains a cornerstone of treatment in resource-limited settings, due to lack of alternatives and its availability in generic fixed-dose combinations.

OBJECTIVE

To review the toxic effects of stavudine and their prevention and management strategies, especially in resource-limited settings.

METHODS

Data from clinical and pharmacological trials in Western countries, as well as prospective cohorts in resource-limited settings, were reviewed.

CONCLUSION

Initiating or switching to less toxic nucleoside analogues whenever possible, or lowering stavudine doses to 30 mg b.i.d., is strongly recommended.

Synthesis and biological activity of chloroethyl pyrimidine nucleosides

The synthesis and biological activity of chloroethyl pyrimidine nucleosides is presented. One of these new nucleosides analogues significantly inhibited cell proliferation, migration and invasion as tested in vitro on the A431 vulvar epidermal carcinoma cell line.

[Efficacy and safety of a reduced-dose of stavudine in HIV-infected patients under immunological and virological stable conditions]

BACKGROUND AND OBJECTIVE

Stavudine (d4T) has shown a favourable short and long-term tolerability profile. Nevertheless, its usage is currently decreasing due to some safety concerns. We aimed to evaluate the efficacy and safety of d4T low-dose-based regimens.

PATIENTS AND METHOD

This was a multicenter and retrospective review chart of patients receiving standard doses of d4T for > or = 6 months (weight > 60 kg: 40 mg/12 h; weight < 60 kg: 30 mg/12 h) and having undetectable viral load for at least 3 months before the d4T dose reduction (weight > 60 kg: 30 mg/12 h; weight < 60 kg: 20 mg/12 h). Immunological and viral parametres, lipid profile and side effects were determined.

RESULTS

A total of 982 patients were included. The main reason for reducing the dose was prevention of toxicity (76%). After 6 months of follow-up, 97% and 84% patients had less than 400 and 50 cp/ml, respectively, and the CD4 cell count increased by 38 cel/ml. Lipids, lipodystrophy and peripheral polineuropathy improved but there was no statistical significance.

CONCLUSIONS

A d4T dose reduction in an immuno-virologically stable population does not affect treatment efficacy. Longer follow-ups are required to confirm improvements in the safety profile.

Systematic review of clinical trials evaluating low doses of stavudine as part of antiretroviral treatment

Stavudine is a nucleoside analogue used for the treatment of HIV-1 infection, as part of highly active antiretroviral treatment. In developing countries, stavudine is used widely, owing to low cost and inclusion in generic fixed-dose combinations. In developed countries, stavudine is now rarely used, although it is highly effective. This is because newer drugs show lower rates of mitochondrial toxicities, such as lipoatrophy, peripheral neuropathy and lactic acidosis. In the development of stavudine, there was evidence that a dosage of 20-30 mg b.i.d. was effective, but the 40-mg b.i.d. dose gained regulatory approval. This review analyses the clinical trials conducted before and after the regulatory approval of stavudine, and shows that the dose of 30 mg b.i.d. has equivalent antiviral efficacy (given the caveats of meta-analysis), with some evidence of lower rates of peripheral neuropathy and lipoatrophy. With limited resources for HIV-1 treatment in developing countries, and only 25% of eligible patients receiving highly active antiretroviral treatment, low-cost treatment options such as stavudine still need to be pursued, if safety can be improved by dose optimisation.

D- and L-2',3'-didehydro-2',3'-dideoxy-3'-fluoro-carbocyclic nucleosides: synthesis, anti-HIV activity and mechanism of resistance

Introducing 2'-fluoro substitution on the 2',3'-double bond in carbocyclic nucleosides has provided biologically interesting compounds with potent anti-HIV activity. As an extension of our previous works in the discovery of anti-HIV agents, D- and L-2',3'-unsaturated 3'-fluoro carbocyclic nucleosides were synthesized and evaluated against HIV-1 in human peripheral blood mononuclear (PBM) cells. Among the synthesized L-series nucleosides, compounds 18, 19, 26 and 28 exhibited moderate antiviral activity (EC50 7.1 microM, 6.4 microM, 10.3 microM, and 20.7 microM, respectively), while among the D-series, the guanosine analogue (35, D-3'-F-C-d4G) exhibited the most potent anti-HIV activity (EC50 0.4 microM, EC90 2.8 microM). However, the guanosine analogue 35 was cross-resistant to the lamivudine-resistant variants (HIV-1M184V). Molecular modeling studies suggest that hydrophobic interaction as well as hydrogen-bonding stabilize the binding of compound 35 in the active site of wild type HIV reverse transcriptase (HIV-RT). In the case of L-nucleosides, these two effects are opposite which results in a loss of binding affinity. According to the molecular modeling studies, cross-resistance of D-3'-F-C-d4G (35) to M184V mutant may be caused by the realignment of the primer and template in the HIV-RTM184V interaction, which destabilizes the RT-inhibitor triphosphate complex, resulting in a significant reduction in anti-HIV activity of the D-guanine derivative 35.

Synthesis and anti-HIV activity of D- and L-thietanose nucleosides

Various D- and L-thietanose nucleosides were synthesized from D- and L-xylose. The four-membered thietane ring was efficiently synthesized by the cyclization of 1-thioacetyl-3-mesylate (4/38) under basic conditions. Condensation with various heterocyclic bases was conducted via Pummerer-type rearrangement to afford various nucleoside derivatives. Among the synthesized nucleosides, D-uridine (23), D-cytidine (24), D-5-fluorocytidine (25), and L-cytidine (52) analogues showed moderate anti-HIV activity, with EC50 = 6.9, 1.3, 5.8, and 14.1 microM, respectively. However, these four nucleoside analogues are cytotoxic in peripheral blood mononuclear and CEM cells. The other nucleosides are neither active nor cytotoxic. Interestingly, the oxetanocin A analogue 33 was not active. Comparison of the minimized reverse transcriptases (RTs) complexed with the corresponding triphosphates of the cytidine analogue 24 and the adenosine analogue 33 by molecular modeling studies showed that there is no difference in the binding mode of the triphosphate of the cytidine analogue 24 to the active site of HIV-1 RT from that of the triphosphate of the adenosine analogue 33. Modeling studies on the initial monophosphorylation step by deoxycytidine kinase showed that the catalytic efficiency of phosphorylation through a nucleophilic attack of the 4'-hydroxyl group of thietanose on the gamma-phosphate of ATP is diminished in the case of L-cytidine analogue (52) due to the increased distance between the 4'-hydroxyl group and the gamma-phosphate.

Mitochondrial toxicity of nucleoside analogues: mechanism, monitoring and management

Nucleoside analogues (NRTIs) are potent antiretroviral medications and are central to effective highly active antiretroviral therapy (HAART). Their intended action is to inhibit HIV reverse transcriptase. Nucleoside analogues also inhibit replication of mitochondrial DNA, and the pathogenesis of many of the toxicities associated with HAART is thought to be NRTI-induced mitochondrial dysfunction. Individuals with HIV infection may be particularly susceptible to clinically significant mitochondrial toxicity due to possible effects of HIV itself on mitochondria. At present there is no reliable method of detecting subclinical mitochondrial toxicity in patients exposed to NRTIs. Clinical awareness of this problem is therefore important to ensure the early detection of significant side effects and to allow timely consideration of changing therapy in those affected. There is no proven, effective therapy for NRTI-associated mitochondrial toxicity other than ceasing the implicated agent, and even with this strategy, resolution of symptoms may be incomplete. Similarly, there are no established methods for preventing mitochondrial toxicity in those on therapy including NRTIs. Micronutrients may have a role, but further study is needed to clarify optimal prevention as well as monitoring strategies.

Hyperlactataemia syndromes associated with HIV therapy

Hyperlactataemia is seen in 8-18.3% of HIV-infected patients taking nucleoside-analogue reverse transcriptase inhibitors (NRTIs). Recent epidemiological studies suggest that most episodes are transient and subclinical. However, symptomatic and occasionally life-threatening cases accompanied by metabolic acidosis and hepatic steatosis (ie, lactic acidosis syndrome) have also been described. Though yet to be fully elucidated, the proposed mechanism is NRTI-induced inhibition of mitochondrial DNA polymerase culminating in derangements in oxidative phosphorylation and lactate homeostasis. Signs and symptoms range from mild hyperlactataemia accompanied by nausea, abdominal discomfort, and weight loss to severe, intractable lactic acidosis complicated by coma and multi-organ failure. Significant progress has recently been made with regard to the natural history of NRTI-related hyperlactataemia. However, other important aspects of the disorder, such as its pathogenesis, predisposing conditions, and management, remain poorly understood. This article reviews the current published work on these issues, identifies areas of controversy, and addresses directions for future research.

Antiretroviral-associated liver injury

ART-related hepatotoxicity can manifest in a variety of ways. Although benign, asymptomatic LEEs predominate, liver injury occurring in the context of either hypersensitivity or hyperlactatemia, represents a medical emergency and mandates immediate cessation of ART. Underpinning this broad spectrum of presentations are several, as yet poorly understood, mechanisms of liver damage that reflect contributions by constituents of HAART and host factors. Thus far, the most significant predisposing condition to emerge from clinical studies is chronic viral hepatitis. A more precise understanding, however, of the processes and factors that underlie ART-related hepatotoxicity is critical not only to the management of liver injury from current antiretroviral drugs but also to the design of safer drugs in the future.

Nucleoside analogues and neuropathy in the era of HAART

BACKGROUND

Sensory neuropathies occur commonly in the setting of HIV infection. Sensory neuropathy (SN) is clearly associated with HIV itself, and in this context develops in association with increased macrophage activation in the peripheral nervous system. A clinically identical SN may also occur as a consequence of exposure to some HIV treatments. In this setting, impaired mitochondrial function is thought to play a role in the development of neurological dysfunction.

OBJECTIVE

This review explores the evidence for the neurotoxicity of HIV and HIV treatments, the effect of nucleoside reverse transcriptase inhibitors on mitochondria, and the likely associations between these.

CONCLUSIONS

Dideoxynucleotide drugs are commonly associated with SN. The nucleoside reverse transcriptase inhibitors inhibit mitochondrial DNA synthesis and may thus exacerbate existing viral-induced nerve damage.

Stereoselective synthesis and antiviral activity of D-2',3'-didehydro-2',3'-dideoxy-2'-fluoro-4'-thionucleosides

As 2',3'-didehydro-2',3'-dideoxy-2'-fluoronucleosides have exhibited interesting antiviral effects against HIV-1 as well as HBV, it is of interest to synthesize the isosterically substituted 4'-thionucleosides in which 4'-oxygen is replaced by a sulfur atom. To study structure-activity relationships, various pyrimidine and purine nucleosides were synthesized from the key intermediate (2R,4S)-1-O-acetyl-5-O-(tert-butyldiphenylsilyl)-2,3-dideoxy-2-fluoro-2-phenylselenyl-4-thio-beta-D-ribofuranoside 8, which was prepared from the 2,3-O-isopropylidene-D-glyceraldehyde 1 in 13 steps. The antiviral activity of the synthesized compounds were evaluated against HIV-1 in human peripheral blood mononuclear (PBM) cells, among which cytidine 17, 5-fluorocytidine 18, adenosine 24, and 2-fluoroadenosine 32 showed moderate to potent anti-HIV activities (EC(50) 1.3, 11.6, 8.1, and 1.2 microM, respectively). It is noteworthy that 2-fluoroadenosine analogue 32 showed antiviral potency as well as high cytotoxicity (IC(50) 1.5, 1.1, and 7.6 microM for PBM, CEM, and Vero, respectively) whereas no other compound showed cytotoxicity up to 100 microM. The cytidine 17 and 5-fluorocytidine 18 analogues showed significantly decreased antiviral activity against the clinically important lamivudine-resistant variants (HIV-1(M184V)), whereas the corresponding D-2'-Fd4 nucleosides showed limited cross-resistance. Molecular modeling studies demonstrated that the larger van der Waals radius as well as the close proximity to Met184 of the 4'-sulfur atom of D-2'-F-4'-Sd4C (17) may be the reasons for the decreased antiviral potency of synthesized 4'-thio nucleosides against the lamivudine-resistant variants (HIV-1(M184V)).

Determination of dosing guidelines for stavudine (2',3'-didehydro-3'-deoxythymidine) in children with human immunodeficiency virus infection

The results of the development of dosing guidelines for stavudine in human immunodeficiency virus (HIV)-infected children are summarized. Included in the integrated analyses were 21 and 33 HIV-infected pediatric and adult patients, respectively, from three phase I-II studies. Data for 21 children and 18 adults who received intravenous doses of 0.125 to 2 and 0.5 to 1 mg/kg of body weight, respectively, were used for the determination of dosing guidelines; exposure data for 16 children and 15 adults who received oral doses of 1 to 2 and 0.5 to 1 mg/kg/day, respectively, were used to validate the dosing recommendations for children. Significant relationships were observed between total body clearance (in milliliters per minute) in children and adults combined and demographic parameters of age, body weight, and body surface area (R(2) = 0.77 to 0.80; P = 0.0001). Models of approximated pediatric dose based on clearance values and direct adult exposure yielded a stavudine dosage of 2 mg/kg/day for children of < or =30 kg of body weight and 1 mg/kg/day (adult dose) for children of >30 kg of body weight.

Significant Toxicities Associated with Antiretroviral Therapy

Use of at least three potent antiretroviral agents has become the standard of care in the management of HIV infection. The potential toxicities associated with highly active antiretroviral therapy (HAART) however, may limit a patient’s ability to adhere to and tolerate these agents. Although a comprehensive discussion of all toxicities associated with HAART is beyond the scope of this article, selected short-term and long-term significant toxicities will be reviewed. Short-term toxicities that will be discussed include abacavir-induced hypersensitivity reactions, efavirenz-associated central nervous system side effects and rash associated with the non-nucleoside reverse transcriptase inhibitors (NNRTIs) and the protease inhibitor (PI) amprenavir. Several long-term toxicities associated with the nucleoside reverse transcriptase inhibitors (NRTIs) are hypothesized to be due to mitochondrial toxicity. These toxicities include myositis and lactic acidosis with hepatic steatosis, pancreatitis and peripheral neuropathy. Some experts also hypothesize that mitochondrial toxicity is responsible for the lipodystrophy syndrome, which includes hyperglycemia, abnormal fat redistribution and dyslipidemia. Finally, indinavir-associated nephrolithiasis, which may present with either short term or long term use will be discussed. This article will provide the practicing pharmacist with a review of these significant toxicities, the implicated agents, incidence, usual clinical presentation, and recommendations for management.

Absolute bioavailability and disposition of (-) and (+) 2'-deoxy- 3'-oxa-4'-thiocytidine (dOTC) following single intravenous and oral doses of racemic dOTC in humans

The purpose of this study was to characterize the pharmacokinetics and determine the absolute bioavailability of 2'-deoxy-3'-oxa-4'-thiocytidine (dOTC) (BCH-10652), a novel nucleoside analogue reverse transcriptase inhibitor, in humans. dOTC belongs to the 4'-thio heterosubstituted class of compounds and is a 1:1 mixture of its two enantiomers, (-) and (+) dOTC. Twelve healthy adult male volunteers each received oral (800-mg) and intravenous (100-mg) doses of dOTC in two study periods separated by at least 7 days. Sixteen plasma samples were obtained over 72 h and assayed for (-) and (+) dOTC, and the resultant data fit by candidate pharmacokinetic models. Data were weighted by the fitted inverse of the observation variance; model discrimination was by AIC. The pharmacokinetic model was a linear, three compartment model, with absorption occurring during one to three first-order input phases, each following a fitted lag time. The model goodness-of-fit was excellent; r(2) ranged from 0.995 to 1.0. The mean absolute bioavailabilities of (+) and (-) dOTC were 77.2% (coefficient of variation [given as a percentage] [CV%], 14) and 80.7% (CV%, 15), respectively. The median steady-state volume of distribution for (+) dOTC, 74.7 (CV%, 19.2) liters/65 kg, was greater than that for (-) dOTC, 51.7 (CV%, 16.7) liters/65 kg (P<0.05). The median total clearance of (+) dOTC was less than that of (-) dOTC, 11.7 (CV%, 17.3) versus 15.4 (CV%, 18.6) liters/h/65 kg, respectively (P< 0.05). The intersubject variability of these parameters was very low. The median terminal half-life of (+) dOTC was 18.0 (CV%, 31.5) h, significantly longer than the 6.8 (CV%, 69.9) h observed for (-) dOTC (P<0.01). No serious adverse events were reported during the study. These results suggest that dOTC is well absorbed, widely distributed, and well tolerated. The terminal half-lives indicate that dosing intervals of 12 to 24 h would be reasonable.

Reversal of human immunodeficiency virus type 1-associated hematosuppression by effective antiretroviral therapy

The immunodeficiency of human immunodeficiency virus type 1 (HIV-1) disease may be due to accelerated destruction of mature CD4+ T cells and/or impaired differentiation of progenitors of CD4+ T cells. HIV-1 infection may also inhibit the production of other hematopoietic lineages, by directly or indirectly suppressing the maturation of multilineage and/or lineage-restricted hematopoietic progenitor cells. To test this hypothesis, the effects of durable viral suppression on multilineage hematopoiesis in 66 HIV-1-seropositive patients were evaluated. Administration of effective antiretroviral therapy resulted in an increase in circulating CD4+ T cell counts and statistically significant increases in circulating levels of other hematopoietic lineages, including total white blood cells, lymphocytes, polymorphonuclear leukocytes, and platelets. These results suggest that a significant lesion in untreated HIV-1 disease may lie at the level of cell production from hematopoietic progenitors.

Abacavir: absolute bioavailability, bioequivalence of three oral formulations, and effect of food

STUDY OBJECTIVES

Study A: to determine the absolute bioavailability of a single 300-mg abacavir hemisulfate tablet. Study B: to determine the bioequivalence of two oral abacavir formulations (300-mg hemisulfate tablet, 100-mg succinate caplet), the effect of food on the bioavailability of the 300-mg hemisulfate tablet, and the bioavailability of the hemisulfate tablet relative to the hemisulfate solution.

DESIGN

Phase I, randomized, open-label, balanced two- (study A) and three- or four-period (study B), crossover studies.

SETTING

Two clinical research centers.

SUBJECTS

Six men infected with the human immunodeficiency virus (HIV), aged 27-39 years (study A), and 18 HIV-infected men and women, aged 21-50 years (study B).

INTERVENTIONS

In study A, all subjects received a single, oral 300-mg tablet of abacavir hemisulfate or a single, intravenous infusion of abacavir hemisulfate 150 mg over 60 minutes. In study B, all subjects received each of three single-dose treatments: three 100-mg abacavir succinate caplets in a fasted state, one 300-mg abacavir hemisulfate tablet in a fasted state, and one 300-mg abacavir hemisulfate tablet with a high-fat breakfast. Twelve subjects in study B also received a fourth treatment of abacavir hemisulfate 300 mg as an oral solution in a fasted state. Plasma samples collected for 24 hours (study A) or 12 hours (study B), and urine samples collected for 12 hours (study A) were analyzed by validated high-performance liquid chromatographic methods.

MEASUREMENTS AND MAIN RESULTS

Abacavir pharmacokinetic parameters were calculated using standard, noncompartmental methods. In study A, the geometric least square (GLS) mean absolute bioavailability of oral abacavir was 83% (range 65-107%). In study B, the hemisulfate tablet was bioequivalent to the succinate caplet, but its time to maximum concentration (Tmax) occurred 30 minutes earlier. Administration of the abacavir hemisulfate tablet with food had no effect on area under the curve from time zero to infinity (AUC0-infinity), decreased maximum concentration (Cmax) by 26%, and delayed Tmax by 38 minutes. The relative bioavailability (GLS mean AUC0-infinity ratio) of the 300-mg abacavir hemisulfate tablet to solution was 101%, Cmax was 11% lower, and Tmax was unchanged. The most common drug-related adverse events associated with abacavir were nausea, vomiting, abdominal pain, and headache, all of which were mild.

CONCLUSION

Based on our results, abacavir is safe and well tolerated and can be administered with or without meals.

New developments in the treatment of HIV disease: An overview

The management of HIV disease has evolved into a complicated and sophisticated subspecialty in recent years. Fourteen drugs, in various combinations, are being used in increasingly complex treatment regimens. The side effects of some of these drugs, as well as certain drug-drug interactions may mimic signs and symptoms of HIV disease itself. Therefore it is imperative for the emergency physician to be knowledgeable about the new medications as well as about selected adverse effect and drug interaction profiles in order to be able to take care of the increasing numbers of HIV-positive patients presenting to emergency departments. This article aims to provide a focused review of these topics. In addition, health care workers with significant exposures to HIV-infected body fluids may present to the emergency department for initial evaluation. This presents a situation whereby emergency physicians may have to prescribe appropriate combinations of antiretroviral agents themselves. Thus familiarity with the basic principles of post-exposure prophylaxis is desirable and current Centers for Disease Control and Prevention guidelines are briefly reviewed.

Safety profile of nevirapine, a nonnucleoside reverse transcriptase inhibitor for the treatment of human immunodeficiency virus infection

Nevirapine (NVP) is a nonnucleoside reverse transcriptase inhibitor widely used in combination with other antiretroviral agents for the treatment of human immunodeficiency virus disease. To establish its safety profile, we conducted a review of data from prospective US and international clinical trials involving a total of 906 adult patients and 468 pediatric patients treated with NVP. Drug-related adverse events were similar in adults and children, with rash and nausea most frequently reported in adults and rash and granulocytopenia most frequently reported in children. A separate analysis of rash based on data from adult patients in controlled trials demonstrated a 16% rate of NVP-attributable rash in these patients. Of patients with NVP-associated rash, 65% developed rash within the first 6 weeks of therapy, and it has been shown that a lower lead-in dose (200 mg/d vs the standard 400 mg/d) for the first 2 weeks of NVP treatment reduces the frequency of drug-associated rash. Serious rash (Stevens-Johnson syndrome [SJS] or SJS/toxic epidermal necrolysis transition syndrome) occurred with an incidence of 0.3% and clinical hepatitis with an incidence of 1.0% among NVP-treated patients in clinical trials. Adverse event data from long-term clinical trials demonstrated a lower incidence of NVP-related adverse events than in short-term trials of NVP therapy. An analysis of abnormal laboratory findings using thresholds similar to those found in the prescribing information for other commonly used antiretroviral agents and data from controlled trials in adults showed that the most frequently observed laboratory abnormalities were elevations in liver function test results. Approximately 50,000 patients in the United States had been treated with marketed NVP at the time of writing, and postmarketing surveillance has supported the overall safety profile observed in clinical trials. NVP has been shown to be well tolerated in both adult and pediatric patients.

Effect of food on the bioavailability of stavudine in subjects with human immunodeficiency virus infection

A randomized, three-way crossover study was carried out to determine the effects of food ingestion on the pharmacokinetics of stavudine (d4T). Fifteen subjects with human immunodeficiency virus (HIV) infection and CD4(+) cell counts of >/=200/microliter received 70 mg of d4T in a fasting state or 1 h before or 5 min after a standardized high-fat breakfast. A 7- to 15-day washout period was included between treatments. Blood and urine were collected before and for 10 h after dosing, and plasma and urine d4T concentrations were determined with a validated radioimmunoassay. Plasma drug concentration-time data were analyzed with a noncompartmental model. The mean maximum plasma drug concentration (Cmax) and the time to Cmax (Tmax) for administration of d4T after a meal were significantly lower and longer (P = 0.0001 for both measures) than those observed in the fasting state, although the area under the concentration-time curve from time zero to infinity (AUC0-infinity) was not significantly different. Neither of these parameters was significantly altered when d4T was taken 1 h before a meal. The bioavailability of d4T taken after a meal was 95% of that observed in the fasting state, and it was 97% when d4T was administered before a meal (P > 0.05 for both comparisons with the fasting state). The results of this study indicate that (i) ingestion of food does not affect the bioavailability of d4T and that patients with HIV infection can take it without regard to meals, and (ii) absorption is essentially complete within 1 h when d4T is administered in the fasted state.

Clinical pharmacokinetics of stavudine

Stavudine (d4T) is a pyrimidine nucleoside analogue used in the treatment of human immunodeficiency virus (HIV) infection. It inhibits viral reverse transcriptase as do zidovudine (AZT), didanosine (ddI), zalcitabine (ddC) and lamivudine (3TC), which comprise the family of nucleoside HIV-reverse transcriptase inhibitors. Stavudine is currently approved by the US Food and Drug Administration for the treatment of patients who have become intolerant to or have failed to response to zidovudine, didanosine or zalcitabine therapy. Oral administration of stavudine results in maximal concentrations within 2 hours and increases linearly as doses increase. The absolute oral bioavailability is high, approaching 100%. There is evidence to suggest that stavudine does not accumulate in the plasma. It distributes into total body water and appears to enter cells by non-facilitated diffusion. Penetration into the cerebrospinal fluid occurs, as does the transfer of the drug across human placental tissue. Stavudine is cleared quickly by both renal and nonrenal processes. The pharmacokinetic properties of stavudine in children are similar to those of adults. The pharmacokinetic parameters of stavudine were not affected by simultaneous administration of didanosine. It appears that stavudine at doses < 2 mg/kg/day is most efficient at increasing CD4 + cell numbers. While stavudine is reported to be less cytotoxic than zidovudine, the principal toxicity in humans is peripheral neuropathy and appears to be related to daily, but not cumulative, doses.

1592U89, a novel carbocyclic nucleoside analog with potent, selective anti-human immunodeficiency virus activity

1592U89, (-)-(1S,4R)-4-[2-amino-6-(cyclopropylamino)-9H-purin-9-yl]-2-cyclo pentene-1-methanol, is a carbocyclic nucleoside with a unique biological profile giving potent, selective anti-human immunodeficiency virus (HIV) activity. 1592U89 was selected after evaluation of a wide variety of analogs containing a cyclopentene substitution for the 2'-deoxyriboside of natural deoxynucleosides, optimizing in vitro anti-HIV potency, oral bioavailability, and central nervous system (CNS) penetration. 1592U89 was equivalent in potency to 3'-azido-3'-deoxythymidine (AZT) in human peripheral blood lymphocyte (PBL) cultures against clinical isolates of HIV type 1 (HIV-1) from antiretroviral drug-naive patients (average 50% inhibitory concentration [IC50], 0.26 microM for 1592U89 and 0.23 microM for AZT). 1592U89 showed minimal cross-resistance (approximately twofold) with AZT and other approved HIV reverse transcriptase (RT) inhibitors. 1592U89 was synergistic in combination with AZT, the nonnucleoside RT inhibitor nevirapine, and the protease inhibitor 141W94 in MT4 cells against HIV-1 (IIIB). 1592U89 was anabolized intracellularly to its 5'-monophosphate in CD4+ CEM cells and in PBLs, but the di- and triphosphates of 1592U89 were not detected. The only triphosphate found in cells incubated with 1592U89 was that of the guanine analog (-)-carbovir (CBV). However, the in vivo pharmacokinetic, distribution, and toxicological profiles of 1592U89 were distinct from and improved over those of CBV, probably because CBV itself was not appreciably formed from 1592U89 in cells or animals (<2%). The 5'-triphosphate of CBV was a potent, selective inhibitor of HIV-1 RT, with Ki values for DNA polymerases (alpha, beta, gamma, and epsilon which were 90-, 2,900-, 1,200-, and 1,900-fold greater, respectively, than for RT (Ki, 21 nM). 1592U89 was relatively nontoxic to human bone marrow progenitors erythroid burst-forming unit and granulocyte-macrophage CFU (IC50s, 110 microM) and human leukemic and liver tumor cell lines. 1592U89 had excellent oral bioavailability (105% in the rat) and penetrated the CNS (rat brain and monkey cerebrospinal fluid) as well as AZT. Having demonstrated an excellent preclinical profile, 1592U89 has progressed to clinical evaluation in HIV-infected patients.

Population pharmacokinetics of stavudine (d4T) in patients with AIDS or advanced AIDS-related complex

The population pharmacokinetics and bioavailability of oral stavudine (d4T; 2',3'-dideoxy-3'-deoxythymidine) was determined in 81 patients with AIDS or AIDS-related complex (ARC) enrolled in phase I and phase I/II dose-ranging trials. Each patient underwent inpatient pharmacokinetic studies following administration of the first oral stavudine dose; 59 patients were restudied after chronic therapy for an average of 19 days. Thirty-three of these patients also received a single intravenous stavudine dose prior to starting an oral regimen. A two-compartment model with first-order absorption and elimination was used as the structural pharmacokinetic model. A basic model provided the following population parameter estimates (interpatient variability expressed in parentheses as percent coefficient of variation): clearance/bioavailability = 30.9 (24.5%) liters/h; volume of distribution/bioavailability = 8.42 (not modeled) liters; volume of distribution at steady state/bioavailability = 68.9 (105%) liters; intercompartmental clearance/bioavailability = 12.4 (26%) liters/h; and first-order absorption rate constant = 1.32 (78.9%) liters/h. In the subset of 33 patients receiving both intravenous and oral doses, the bioavailability of stavudine was estimated to be 99.1% (18.5%). Total body weight, stage of disease (AIDS versus ARC), and an oral stavudine dose of > or = 200 mg were found to have a statistically significant but a clinically marginal effect on the estimate of the oral clearance of stavudine. This analysis shows the high degree of bioavailability of stavudine in patients with AIDS and ARC and the relatively low degree of interpatient variability in oral drug clearance compared with those of other nucleosides. Population pharmacokinetic analysis is a useful tool for assessing the combined effects of several patient variables on the pharmacokinetic properties of drugs in human immunodeficiency virus-infected patients.