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

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.

Pharmacologic consideration for the use of antiretroviral agents in the elderly

The prevalence of human immunodeficiency virus (HIV) infection among people older than 50 years is increasing. HIV-infected patients require lifelong treatment with antiretroviral agents to suppress viral replication and maintain immune function. The use of antiretroviral agents in the elderly can be complicated by multiple chronic comorbidities and coadministered non-HIV medications. The pharmacokinetics of antiretroviral agents may be altered due to age-related decrements in hepatic and renal function. The elderly may be more sensitive than younger people to antiretroviral drug toxicity. A better understanding of the pharmacokinetics of antiretroviral agents in the elderly is of importance for the successful management of complex antiretroviral regimens in this population.

Clinical Toxicity of Highly Active Antiretroviral Therapy in a Home-Based AIDS Care Program in Rural Uganda

BACKGROUND

We evaluated clinical toxicity in HIV-infected persons receiving antiretroviral therapy (ART) in Uganda.

METHODS

From May 2003 through December 2004, adults with a CD4 cell count < or =250 cells/microL or World Health Organization stage 3/4 HIV disease were prescribed ART. We calculated probabilities for time to toxicity and single-drug substitution as well as multivariate-adjusted hazard ratios for development of toxicity.

RESULTS

ART (stavudine plus lamivudine with nevirapine [96%] or efavirenz [4%]) was prescribed for 1029 adults, contributing 11,268 person-months of observation. Toxicities developed in 543 instances in 411 (40%) patients (incidence rate = 4.47/100 person-months): 36% peripheral neuropathy (9% severe); 6% rash (2% severe); 2% hypersensitivity reaction; < or =0.5% acute hepatitis, anemia, acute pancreatitis, or lactic acidosis; and 13% other. Probabilities of remaining free from any toxicity at 6, 12, and 18 months were 0.76, 0.59, and 0.47 and from any severe toxicity at 6, 12, and 18 months were 0.92, 0.86, and 0.85, respectively. For 217 patients (21%), 222 single-drug substitutions were made, mostly because of peripheral neuropathy or rash.

CONCLUSIONS

Clinical toxicities were common, but no patients discontinued ART because of toxicity. The most common toxicities, peripheral neuropathy and rash, were managed with single-drug substitutions. In resource-limited settings, toxicity from ART regimens containing stavudine or nevirapine is manageable but more tolerable regimens are needed.

Pharmacokinetics of the antiviral agent beta-L-3'-fluoro-2',3'-didehydro-2',3'-dideoxycytidine in rhesus monkeys

beta-L-3'-Fluoro-2',3'-didehydro-2',3'-dideoxycytidine (L-3'-Fd4C) is a potent and selective antiretroviral nucleoside with activity against lamivudine-resistant human immunodeficiency virus type 1 (HIV-1) and hepatitis B virus (HBV) in vitro. The pharmacokinetics of L-3'-Fd4C were characterized in three rhesus monkeys given single intravenous and oral doses. A two-compartment open model was fitted to the plasma and urine data. Plasma concentrations declined in a biexponential fashion with an average beta half-life of 12.45 h and central and steady-state volumes of distribution of 0.43 and 1.90 liters/kg, respectively. The average systemic and renal clearance values were 0.23 and 0.08 liters/kg, respectively, and the apparent mean terminal half-life of the oral dose was 12.5 h. The serum concentrations exceeded the 90% effective concentration value for lamivudine-resistant and wild-type HIV-1 after oral administrations. A large variation was observed in the oral bioavailability, which ranged from 15 to 31%. To determine whether the bioavailability may be improved by using a basic buffer solution, the oral dose was repeated to the same animals in a sodium bicarbonate solution. The bioavailability of L-3'-Fd4C administered with sodium bicarbonate was not significantly different from the bioavailability when the oral dose was administered in the absence of buffer (P = 0.49), suggesting that further development of this compound may warrant other approaches, such as development of a prodrug to improve its oral absorption.

Preparation and pharmacokinetics of 11C labeled stavudine (d4T)

Stavudine, a potent antiviral agent for treating human immunodeficiency virus (HIV) infections, was radiolabeled with (11)C by methylation of a specifically designed precursor, 5'-O-(2-tetrahydropyranyl)-5-bromo-2',3'-didehydro-3'-deoxythymidine, with (11)C H(3)I. The radiolabeled drug was isolated by reverse phase HPLC. A total time of approximately 45 minutes was required for synthesis, purification and isolation of (11)C stavudine with chemical and radiochemical purities of greater than 98%. (11)C stavudine was combined with unlabeled drug (2.0 mg/kg) and used to study its pharmacokinetics in rats by measurement of radioactivity in excised tissues. In this species, there was rapid accumulation of drug in all tissue. In all tissues, with the exceptions of testis and brain, highest concentrations of drug were detected at 5 minutes after injection and decreased monotonically thereafter. The peak concentration (microg/g) of stavudine in blood was 1.78 +/- 0.16 and similar levels were achieved in most other tissues; heart 1.66 +/- 0.11, lung 1.60 +/- 0.15, liver 2.13 +/- 0.17, spleen 1.61 +/- 0.15, adrenal 1.47 +/- 0.20, stomach 1.40 +/- 0.11, GI tract 1.44 +/- 0.14, skeletal muscle 1.38 +/- 0.15 and bone 1.30 +/- 0.16. Much higher peak concentrations were achieved in kidney; 7.23 +/- 0.57 microg/g. Concentrations in testis were lower and remained relatively constant over 1 hour; peak 0.62 +/- 0.14 microg/g at 15 min Brain concentrations were low but increased monotonically over time; peak 0.26 +/- 0.02 microg/g at 60 min. Future PET studies with this radiopharmaceutical will allow in vivo measurements of the pharmacokinetics of stavudine in both animal models and human subjects.

The cellular pharmacology of nucleoside- and nucleotide-analogue reverse-transcriptase inhibitors and its relationship to clinical toxicities

Nucleoside- and nucleotide-analogue reverse-transcriptase inhibitors (NRTIs) require intracellular phosphorylation for anti-human immunodeficiency virus (HIV) activity and toxicity. Long-term toxicities associated with NRTIs may be related to overactivation of this process. In vitro experiments have shown increased rates of NRTI and endogenous nucleoside phosphorylation to be associated with cellular activation. Patients with advanced HIV disease often have overexpression of cytokines, which corresponds to an elevated cellular activation state. These patients also have higher rates of NRTI phosphorylation and NRTI toxicity, suggesting an interaction between a proinflammatory biological state, NRTI phosphorylation, and toxicity. Studies suggest that women may have higher rates of NRTI phosphorylation than do men, as well as increased risk for NRTI-induced toxicity. Future research is needed to understand the NRTI activation process and improve the long-term toxicity profile of NRTIs. Such research should include comparisons of NRTI phosphorylation according to sex and cellular activation state (i.e., elevated vs. low).

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.

Antiviral activity and pharmacokinetics of 1-(2,3-dideoxy-2-fluoro-beta-L-glyceropent-2-enofuranosyl)cytosine

1-(2,3-Dideoxy-2-fluoro-beta-L-glyceropent-2-enofuranosyl)cytosine (L-2'-Fd4C) is an L-nucleoside analogue with both anti-human immunodeficiency virus (HIV) and anti-hepatitis B virus (HBV) activity with median effective concentrations of 0.12 microM in peripheral blood mononuclear cells and 0.002 microM in HepG2-2.2.15 cells, respectively. The purpose of this study was to examine the antihepadnavirus potency and pharmacokinetics of L-2'-Fd4C in vivo. HBV-transgenic mice treated intraperitoneally with L-2'-Fd4C showed a reduction of HBV levels in their blood comparable to that produced by lamivudine. The pharmacokinetics of L-2'-Fd4C in rhesus monkeys was evaluated after intravenous and oral administration. The concentrations in plasma declined in a biexponential manner after intravenous administration, with a long terminal-phase half-life of 5.02 h. The steady-state volumes of distribution and systemic clearance were 1.09 liter x kg(-1) and 0.25 liter x h(-1) x kg(-1), respectively, with a renal clearance of 0.16 liter x h(-1) x kg(-1). The oral bioavailability was approximately 44%. About 53% of the compound administered intravenously and 19% of that administered orally were recovered unchanged in the urine within the 24-h urine collection period, and no other metabolite was detected. The compound penetrated the central nervous system at concentrations that exceeded the median effective antiviral concentration against HIV in cell cultures. Based upon these observations, further testing to develop this agent for treatment of HIV and HBV infections is warranted.

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.

A phase II randomized study of the virologic and immunologic effect of zidovudine + stavudine versus stavudine alone and zidovudine + lamivudine in patients with >300 CD4 cells who were antiretroviral naive (ACTG 298)

Before the development of multidrug regimens for treatment of patients with HIV infection single or dual nucleoside therapy was the standard of care. The present study was designed to examine the relative short (12-week) and long-term (48-week) activity of zidovudine (ZDV) vs stavudine (d4T) vs the combination in antiretroviral naive patients. The study was modified so that lamivudine (3TC) was added to ZDV after 12 weeks of monotherapy. A total of 129 subjects entered the study; however, not all were followed for 48 weeks as the study was terminated early due to changing standards of care. The median baseline viral load and CD4 cell count were 10,008 copies/ml and 407 cells/mm(3), respectively. There were no significant differences in the initial (12-week) change in viral load across the three arms. The viral load reduction at 48 weeks was greater in the ZDV/ZDV plus 3TC arm, with an average change of -0.91 log(10) copies/ml than in the d4T alone (-0.47 log(10) copies/ml) or d4T plus ZDV (-0.33 log(10) copies/ml), p = 0.03 and 0.02, respectively. There was a marginally significant increase in the CD4 cell count at Week 12 in the d4T arm as compared to the ZDV/ZDV plus 3TC arm. In general the treatments were well tolerated. The combination of d4T plus ZDV did not result in additional antiviral suppression as compared to either drug alone at 12 weeks and appeared to have less antiviral activity after Week 12. Based on this study and other data, combining d4T and ZDV is not recommended.

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.

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.

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.

Acute pancreatitis in human immunodeficiency virus-infected patients: a review

Acute pancreatitis is a clinical condition that develops when active pancreatic inflammation is induced by stimuli noxious to the pancreas. Patients infected with human immunodeficiency virus (HIV) often have histologic abnormalities of the pancreas, and acute pancreatitis is much more common in HIV-infected patients than in the general population. This article reviews the epidemiology and etiology of acute pancreatitis in HIV-infected patients. The clinical presentation and treatment of acute pancreatitis in HIV-infected patients are also reviewed.

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.

The in vivo effects of combination antiretroviral drug therapy on peripheral blood CD34+ cell colony-forming units from HIV type 1-infected patients

This study investigated the effects of a combination antiretroviral drug regimen (indinavir and two nucleoside analogs or ritonavir and saquinavir) on the levels of CD34+ colony-forming units (CFU-Cs) in the peripheral blood of HIV-1+ patients. Ten patients who were receiving combination antiretroviral drug therapy were studied and their peripheral blood CD34+ CFU-Cs were measured prior to, 1 month after, and 4 to 6 months after the commencement of therapy. The levels of CD4+ T cells increased significantly in these patients (paired t test, p = 0.0027) and plasma viral load became undetectable in all but one patient studied. Measurements of the CFU-Cs showed that their levels tended to increase on the commencement of therapy, and these levels became significantly higher than baseline by 4-6 months (paired t test, p = 0.0293). Analysis of the different colony phenotype demonstrated that the main contributor to this increase consisted of burst-forming unit erythroid (BFU-E) cells. These data also demonstrated that there was an inverse correlation between the rise in CFU-Cs at 4-6 months compared with CD4+ cell, CD8+ cell, and neutrophil counts, and hemoglobin concentration, at baseline. The demonstrated increase in the levels of CD34+ CFU-Cs suggests that HIV-1 may have an inhibitory effect on these cells in vivo, and that this inhibition may be abrogated by suppression of viral replication.

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.

The transport of the anti-HIV drug, 2',3'-didehydro-3'-deoxythymidine (D4T), across the blood-brain and blood-cerebrospinal fluid barriers

1. The brain is a site of infection, viral replication and sanctuary for HIV-1. The treatment of HIV-1 infection therefore requires that an effective agent be delivered to the brain. 2',3'-Didehydro-3'-deoxythymidine (D4T) is a nucleoside analogue which has been shown to have beneficial clinical effects in the treatment of HIV infection. However, although D4T has been detected in human CSF, the ability of this drug to cross both the blood-brain and blood-cerebrospinal fluid (CSF) barriers and gain entrance into the brain tissue is not known. 2. This study examined the CNS entry of D4T by means of the bilateral vascular brain perfusion technique in the anaesthetized guinea-pig. 3. The results indicated that [3H]-D4T had a limited ability to cross the blood-brain barrier (BBB), which was not significantly greater than D-[14C]-mannitol (a slowly penetrating marker molecule). Although D4T was found to cross the blood-CSF barrier, the presence of D4T in the CSF did not reflect levels of the drug in the brain tissue. 4. These results can be related to the measured low lipophilicity of D4T, the higher paracellular permeability characteristics of the choroid plexus (blood-CSF barrier) compared to the BBB, and the sink action nature of the CSF to the brain tissue. 5. In conclusion, these animal studies suggest that D4T may only penetrate the brain tissue to a limited extent and consideration should be given to these findings in the clinical situation.

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.

Pharmacokinetics and safety of a single dose of stavudine (d4T) in patients with severe hepatic impairment

This open-label study enrolled five subjects with biopsy-proven cirrhosis and moderate to severe hepatic impairment (Child-Pugh classification grade B or C) and five age- and gender-matched controls. All subjects received a single 40-mg oral dose of stavudine (d4T). Stavudine pharmacokinetics in subjects with hepatic impairment were similar to those in age- and gender-matched control subjects and were not substantially different from those previously observed in human immunodeficiency virus-infected patients. Based on these findings, stavudine use does not require modification of the dose or dosing interval for patients with liver disease.

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.

Quantitative molecular monitoring of HIV-1 RNA during antiretroviral therapy

Plasma HIV-1 RNA testing was used to monitor 43 HIV-1 infected patients newly placed on antiretroviral therapy or whose therapy had been recently changed. A polymerase chain reaction kit was used to measure HIV-1 RNA in clinical samples or frozen plasma. The cutoff of this test was 200 RNA copies/ml. The first group (11 patients) was stable on long-term zidovudine monotherapy when switched to stavudine. The HIV-1 RNA of three patients who had a regular decline in CD4+ T cell count did not change despite this switch, with a mean follow-up of 630 days. The HIV-1 RNA copy numbers of eight patients whose CD4+ T cell counts were stable declined an average of 0.53 log10 between days 90 and 650. The second group (14 patients) was on long-term zidovudine monotherapy and had declining CD4+ T cell counts over the past 6 months. Lamivudine was added to this regimen on day 0. HIV-1 RNA copy number decreased rapidly within 30 d, reaching -0.86 log10 on day 90, and this effect was maintained thereafter, with a mean follow-up of 161 days. There was a concomitant mean gain of +33 CD4+ T cells on day 90. The third group (nine patients) had never received anti-retroviral therapy and was given zidovudine+didanosine. HIV-1 RNA copy number decreased in all cases but one, reaching -1.31 log10 on day 150. This decrease was transient in three cases. The last group (nine patients) had also not had previous anti-retroviral therapy and was given zidovudine + didanosine + lamivudine in combination. HIV-1 RNA copy numbers declined rapidly in all cases, to below the cutoff in eight cases within a mean period of 50.5 days. The CD4+ cell counts increased by 164 cells/microliter on day 14 and by 201 cells/microliter on day 180. The response to therapy of the total population of 43 patients varied according to cases. The relative changes in p24 antigen compared to HIV-1 RNA also differed between patients. Measurement of HIV-1 viremia appears to be a valuable tool in current practice for individualizing therapy.

Treatment of HIV infection. Tolerability of commonly used antiretroviral agents

There are a number of agents available that are active against HIV. Eight drugs are already licensed in the US: the nucleoside analogue reverse transcriptase inhibitors--zidovudine, didanosine, zalcitabine, stavudine and lamivudine--and the HIV protease inhibitors--saquinavir, indinavir and ritonavir. Antiretroviral drugs have been given as monotherapy, often as sequential monotherapy, and in alternating or simultaneous combinations. Since combination therapy has recently been shown to be superior to monotherapy, antiretrovirals will increasingly be given in combination. All available antiretroviral drugs show considerable toxicity complicating their use. In this article we describe the adverse effects of the above mentioned nucleoside analogues used in monotherapy and of several combinations of antiretroviral drugs. No unexpected toxicities were found in several different combinations tested to date and, for most combinations, no synergistic toxic effects have been reported.

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.