Stavudine in patients with AIDS and AIDS-related complex: AIDS clinical trials group 089

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.

Bioequivalence evaluation of two marketed brands of stavudine 40mg capsules in healthy human South African volunteers

Stavudine (d4T), a thymidine nucleoside analogue has been effectively used for treatment of patients infected with HIV. A randomized, two-way, crossover study was conducted in 24 fasting, healthy, Caucasian male volunteers to compare plasma pharmacokinetic (PK) profile and single-dose tolerability of a new d4T formulation (Stavir, Cipla Ltd, India; 40 mg capsule, test, T) with that of reference (R) formulation (Zerit), Bristol-Myers Squib, NJ, USA; capsule, 40 mg). Each volunteer received T and R formulation separated by at least 10 days of drug free wash-out period. Plasma concentrations of d4T, determined upto 24h post-dose by a validated LC-MS/MS assay were utilized to assess PK parameters such as maximum observed plasma concentration (Cmax), time to Cmax (tmax), and area under plasma concentration curve (AUC(infinity)). The primary plasma PK parameters, Cmax, and AUC(infinity), of anti-retroviral were comparable for either of the formulations. tmax was achieved within an hour suggesting rapid absorption of d4T from both formulations. Geometric mean ratios (GMR) (percentage reference) of AUC(infinity) and Cmax, and their 90% confidence intervals (CI) were 106.32 [102.52-110.26] and 102.32 [90.25-116.00], respectively. As the 90% CI of GMR were entirely within 80-125% for log-transformed parameters, two formulations were considered bioequivalent, in the extent and rate of absorption. Both formulations exhibited similar tolerability under fasting conditions.

Intermittent administration of high-dose stavudine to nucleoside-experienced individuals infected with HIV-1

To explore a novel method to use nucleosides in heavily treated patients, 4-week cycles of high-dosage (280 mg/d) stavudine were given to 11 asymptomatic patients who had previously received an average of 6 years of nucleoside reverse transcriptase inhibitors (NRTIs). The stavudine dose was targeted to produce a calculated steady-state concentration of 1.5 microM (336 ng/mL). Participants received stavudine for the first 4 weeks, after which it was discontinued for 4 weeks. Additional 4-week drug cycles were given if plasma HIV-1 RNA levels increased to at least 75% of baseline values. The 11 subjects received 38 cycles (average, 3.5 cycles per subject) during the 44-week study. Stavudine was well tolerated. Considering all data, there was a median 0.65 log(10) reduction in viral load as well as a median increase in CD4 cell count of 110/mm3 at the end of the cycles. However, plasma viremia increased and CD4 cell counts decreased between cycles. Viral load and CD4 cell responses were similar for up to 4 successive cycles. This suggested that increasing viral resistance was not a problem, as reflected by the acquisition of only one new nucleoside reverse transcriptase mutation among the participants. Significant relationships between stavudine exposure and changes in plasma HIV RNA levels were observed. A similar approach might be considered using a more potent regimen for patients in whom resistance to nucleosides is a major reason for therapeutic failure.

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.

Macrocytosis in patients on stavudine

We retrospectively reviewed the effects on the erythrocyte mean corpuscular volume (MCV) of the use of stavudine-including antiretroviral regimens in both zidovudine-naive and zidovudine-experienced HIV-infected patients. Macrocytosis was commonly observed among patients on stavudine-based regimens although the MCV usually stabilized at a lower level than that observed with zidovudine.

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.

Wild-type and YMDD mutant murine leukemia virus reverse transcriptases are resistant to 2',3'-dideoxy-3'-thiacytidine

The antiretroviral nucleoside analog 2',3'-dideoxy-3'-thiacytidine (3TC) is a potent inhibitor of wild-type human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT). A methionine-to-valine or methionine-to-isoleucine substitution at residue 184 in the HIV-1 YMDD motif, which is located at the RT active site, leads to a high level of resistance to 3TC. We sought to determine whether 3TC can inhibit the replication of wild-type murine leukemia virus (MLV), which contains V223 at the YVDD active site motif of the MLV RT, and of the V223M, V223I, V223A, and V223S mutant RTs. Surprisingly, the wild type and all four of the V223 mutants of MLV RT were highly resistant to 3TC. These results indicate that determinants outside the YVDD motif of MLV RT confer a high level of resistance to 3TC. Therefore, structural differences among similar RTs might result in widely divergent sensitivities to antiretroviral nucleoside analogs.

Management of the adverse effects of antiretroviral therapy and medication adherence

A commonly cited cause of poor adherence to highly active antiretroviral therapy (HAART) is adverse drug reactions. Short-term adverse effects are potential threats to successful introduction and maintenance of HAART. The long-term toxicities of HAART are still emerging and being defined, as evidenced by the recently described metabolic disorders (i.e., the syndrome of maldistribution, hyperlipemia, glucose intolerance and insulin resistance). With 14 licensed agents in 2000, other agents in common use, and numerous combinations of >/=3 drugs, awareness and recognition of adverse effects are increasingly important for clinicians and patients. The common adverse drug reactions encountered with HAART, including new agents and their impact on patient adherence, are reviewed. Current strategies to anticipate and mitigate adverse effects are summarized.

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.

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.

Anti-HIV Antiviral Activity of Stavudine in a Thymidine Kinase-Deficient Cellular Line

Stavudine (d4T) is a potent inhibitor of human immunodeficiency virus type 1 (HIV-1) reverse transcriptase. It is known that stavudine is metabolized in cells to the mono-, di- and triphosphate nucleotides but the enzymes responsible for its phosphorylation are as yet unidentified. In particular, there are conflicting results concerning the role of thymidine kinase 1 (TK1) in stavudine metabolism. To gain new insights into this phenomenon we analysed the antiviral activity of stavudine in a TK1-deficient, resistant cell line. The results indicate that TK1 is responsible for the phosphorylation of stavudine but it is not the only enzyme involved in its activation. The other enzyme(s) that might be involved in the metabolism of stavudine, however, are not able to phosphorylate stavudine with the same efficiency as TK1. Since it has been shown that prolonged treatment with zidovudine may induce an in vivo defect in TK1 activity, it is tempting to speculate that patients treated for a long time with zidovudine could be resistant to further treatment with stavudine.

Genotypic and Phenotypic Resistance to Stavudine after Long-Term Monotherapy

Protocol BMS 020 was a double-blind, prospective clinical trial in which two different doses of stavudine (20 and 40 mg twice daily) were compared in human immunodeficiency virus (HlV)-infected patients with previous exposure to zidovudine for longer than 16 weeks. Genotypic and phenotypic resistance to both zidovudine and stavudine were examined after at least 2 years of stavudine monotherapy. None of 35 tested individuals harboured the codon 50 and/or 75 mutations previously described to be associated with stavudine resistance. However, more than 80% of the individuals carried mutations associated with zidovudine resistance, despite all these patients having stopped zidovudine at least 2 years earlier. Significant phenotypic resistance to stavudine was observed only in 2 of 5 tested individuals, although IC50 values were increased only 6.6- and 9.2–fold, respectively. These two patients had suffered a decline in their CD4 count, and one of them had high levels of plasma viraemia. The sequence analysis of the reverse transcriptase (RT) gene (aa 30 to 240) in these five patients revealed no changes that could be involved in stavudine resistance. In contrast, and despite having stopped treatment with zidovudine more than 2 years before, phenotypic resistance to zidovudine was observed in all five subjects, with IC50 values raised by more than 75-fold in all of them. Moreover, all harboured codon substitutions within the RT gene associated with zidovudine resistance, and these mutations remained in viral genomes examined after virus co-culture, suggesting that they provided some biological advantage to mutants, even in the absence of drug pressure. In conclusion, both genotypic and phenotypic resistance to stavudine seem to be a rare event in patients exposed to the drug, even after long periods of exposure.

Frequency and determinants of use of antiretroviral and prophylactic therapies against Pneumocystis carinii Pneumonia (PCP) before AIDS diagnosis in Italy

To determine the frequency and the determinants of use of antiretroviral drugs and prophylaxis for Pneumocystis carinii Pneumonia (PCP) among HIV-infected individuals before AIDS diagnosis, a questionnaire was sent to all physicians reporting at least one AIDS case during the first six months of 1994 to the Italian National AIDS Registry. Information on cases diagnosed between 1 January and 31 March 1995 was collected. Information was obtained for 878 (66.4%) of the 1323 persons with AIDS: 447 (50.9%) had received antiretroviral drugs and 343 (39.1%) PCP prophylaxis, whereas 303 cases (34.5%) had received both. Individuals who became aware of being HIV-positive shortly before AIDS diagnosis were less likely to have started antiretroviral therapy (adjusted odds ratio (AOR): 0.05, 95% CI: 0.03-0.09). Homosexual men and heterosexuals were more likely to begin therapy (AOR: 1.40, 95% CI: 0.83-2.37 and AOR: 1.79, 95% CI: 1.05-3.05, respectively) compared to injecting drug users. Individuals living in Southern Italy and foreigners were less likely to start therapy (AOR: 0.75, 95% CI: 0.49-1.16 and AOR: 0.40, 95% CI: 0.15-1.09, respectively) compared to those living in Northern Italy. Results were similar for PCP prophylaxis. Lack of awareness of HIV infection, HIV exposure category, and geographical area were the most important factors associated with treatment before AIDS diagnosis.

Antiretroviral therapy in the pregnant woman

The use of antiretroviral agents to treat patients infected with HIV has become increasingly complex. Obstetricians caring for the pregnant woman infected with HIV must, no less than the HIV specialist, be familiar with the various medications now available. This article profiles each of the antiretroviral agents currently available, with a focus on issues relevant to the pregnant patient. Strategies for treating the nonpregnant patient and considerations for the use of these strategies in pregnancy also are discussed. Additional information about prophylaxis for common opportunistic infections is included.

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.

Comparative metabolism of the antiviral dimer 3'-azido-3'-deoxythymidine-P-2',3'-dideoxyinosine and the monomers zidovudine and didanosine by rat, monkey, and human hepatocytes

AZT-P-ddI is an antiviral heterodimer composed of one molecule of 3'-azido-3'-deoxythymidine (AZT) and one molecule of 2',3'-dideoxyinosine (ddI) linked through their 5' positions by a phosphate bond. The metabolic fate of the dimer was studied with isolated rat, monkey, and human hepatocytes and was compared with that of its component monomers AZT and ddI. Upon incubation of double-labeled [14C]AZT-P-[3H]ddI in freshly isolated rat hepatocytes in suspension at a final concentration of 10 microM, the dimer was taken up intact by cells and then rapidly cleaved to AZT, AZT monophosphate, ddI, and ddI monophosphate. AZT and ddI so formed were then subject to their respective catabolisms. High-performance liquid chromatography analyses of the extracellular medium and cell extracts revealed the presence of unchanged dimer, AZT, 3'-azido-3'-deoxy-5'-beta-D-glucopyranosylthymidine (GAZT), 3'-amino-3'-deoxythymidine (AMT), ddI, and a previously unrecognized derivative of the dideoxyribose moiety of ddI, designated ddI-M. Trace extracellular but substantial intracellular levels of the glucuronide derivative of AMT (3'-amino-3'-deoxy-5'-beta-D-glucopyranosylthymidine [GAMT]) were also detected. Moreover, the extent of the formation of AMT, GAZT, and ddI-M from the dimer was markedly lower than that with AZT and ddI alone by the hepatocytes. With hepatocytes in primary culture obtained from rat, monkey, and human, large interspecies variations in the metabolism of AZT-P-ddI were observed. While GAZT and ddI-M, metabolites of AZT and ddI, respectively, as well as AZT 5'-monophosphate (MP) and ddI-MP were detected in the extracellular media of all species, AMT and GAMT were produced only by rat and monkey hepatocytes. No such metabolites were formed by human hepatocytes. The metabolic fate of the dimer by human hepatocytes was consistent with in vivo data recently obtained from human immunodeficiency virus-infected patients.

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.

Effects of drugs on 2',3'-dideoxy-2',3'-didehydrothymidine phosphorylation in vitro

Drugs commonly administered to patients infected with the human immunodeficiency virus (HIV) have been studied for their propensity to alter the intracellular phosphorylation of the anti-HIV nucleoside analog stavudine (2',3'-dideoxy-2',3'-didehydrothymidine; d4T) in peripheral blood mononuclear cells (PBMCs) and U937 cells in vitro. PBMCs isolated from the blood of healthy volunteers were stimulated by the mitogen phytohemagglutinin (10 microg/ml) for 72 h. Stimulated PBMCs (3 x 10(6) cells/plate) were then incubated with [3H]d4T (0.65 microCi; 3 microM) and either acyclovir, dapsone, ddC, ddI, fluconazole, foscarnet, ganciclovir, itraconazole, lobucavir, ranitidine, ribavirin, rifampin, sorivudine, sulfamethoxazole, trimethoprim, lamivudine (3TC), zidovudine, or thymidine (30 and 300 microM) for 24 h. Doxorubicin and drugs showing some evidence of inhibition were also studied at 0.3 and 3 microM. Cells were extracted overnight with 60% methanol prior to analysis by radiometric high-performance liquid chromatography. Additional data for nine of the drugs were obtained by incubation with [3H]d4T in U937 cells for 24 h. The effect of d4T (0.2 to 20 microM) on zidovudine (0.65 microCi; 0.018 microCi) phosphorylation was also studied. Zidovudine significantly reduced d4T total phosphates in PBMCs and U937 cells (in PBMCs to 33% [P < 0.001] and 17% [P < 0.001] of that in control cells at 3 and 30 microM, respectively). A small reduction in zidovudine phosphorylation was seen with d4T but only at d4T:zidovudine ratios of 100 and 1,000. Of the other compounds screened, only thymidine, ribavirin, and doxorubicin produced inhibition of d4T phosphorylation in both PBMCs and U937 cells. However, doxorubicin was cytotoxic at 3 microM. The decrease in d4T phosphorylation in the presence of ribavirin is consistent with previous findings with zidovudine. Although ddC significantly inhibited the phosphorylation of d4T in PBMCs, this was not seen in U937 cells, and it is probable that the findings in PBMCs are related to mitochondrial toxicity [based on 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide cytotoxicity assay]. The only drugs screened which may interfere with d4T phosphorylation at clinically relevant concentrations were zidovudine, ribavirin, and doxorubicin.

Phase I dose-escalation pharmacokinetics of AZT-P-ddI (IVX-E-59) in patients with human immunodeficiency virus

3'-Azido-3'-deoxythymidilyl-(5',5')-2',3'-dideoxy-5'-inosinic acid (AZT-P-ddI, IVX-E-59, Scriptene) is a heterodimer composed of one molecule of 3'-azido-3'-deoxythymidine (zidovudine or AZT) and one molecule of 2',3'-dideoxyinosine (didanosine or ddI) linked through their 5' positions by a phosphate bond. AZT-P-ddI exhibits enhanced antiviral activity and selectivity in vitro compared with AZT and ddI alone. The pharmacokinetics of AZT-P-ddI were studied in 12 patients with human immunodeficiency virus (HIV) who had CD4+ cell counts higher than 200 cells/mm3. Isotopic preparations of (14C)-AZT-P-(3H)-ddI were administered intravenously (50 mg and 100 mg) to eight patients; 1 month later these patients were crossed over to oral administration (100 mg and 200 mg). A second group of patients (n = 4) received only a 450-mg oral dose of AZT-P-ddI. Plasma levels of unchanged AZT-P-ddI after intravenous infusion declined rapidly and were undetectable 0.75 hours after the end of infusion, whereas the parent compound was not detected after oral administration, indicative of a very rapid metabolism. The parent entity was enzymatically cleaved in vivo yielding the two constituent drugs AZT and ddI, which were subsequently subjected to their respective pharmacokinetic and metabolic processes. The beta-glucuronide derivative of AZT (GAZT) represented the major metabolite of AZT, but there were no detectable levels of the toxic metabolite 3'-amino-3'-deoxythymidine (AMT). A major and previously unrecognized in vivo metabolite of ddI, referred as ddI-M, was detected in plasma and urine. Analysis by high-field proton nuclear magnetic resonance and mass spectrometry led to the identification of ddI-M as being R(-)-dihydro-5-(hydroxymethyl)-2(3H)-furanone. The formation of AZT and ddI metabolites was increased after oral administration of AZT-P-ddI compared with the intravenous infusion, with an area under the concentration-time curve (AUC) ratio of metabolite to AZT and metabolite to ddI being 7.7 and 5.7 (oral) and 3.8 and 1.1 (intravenous), respectively. The newly identified ddI-M exhibited sustained plasma levels for extended time periods with an apparent elimination half-life (t1/2) of approximately 10 hours after oral administration of AZT-P-ddI. Recovery of radioactivity associated with 3H and 14C in urine was essentially complete within 48 hours after oral and intravenous administration of AZT-P-ddI. The oral bioavailability of AZT (64.7-67.3%) and ddI (33.6-42.9%) and the other pharmacokinetic parameters were consistent with previous data reported with each nucleoside analog alone or in combination therapy.

What is new in clinical research of viral diseases of the skin

Viral diseases of the skin have become a much more serious problem with the increasing number of patients immunosuppressed by either AIDS or cancer chemotherapy. The emphasis in research on the diagnosis and treatment of these diseases is similar to that on the bacterial diseases several decades ago.

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.

Radioimmunoassay for quantitation of 2',3'-didehydro-3'-deoxythymidine (D4T) in human plasma

2',3'-Didehydro-3'-deoxythymidine (D4T, or stavudine) has been recently approved for the treatment of AIDS. In the present study, a specific and sensitive radioimmunoassay (RIA) was developed for the quantitation of D4T in human plasma. The RIA is a double-antibody competitive binding assay which uses anti-D4T antiserum raised in rabbits as the primary antibody, a tritiated derivative of D4T as the radioactive tracer, and goat anti-rabbit immunoglobulin G as the secondary antibody. No cross-reaction between D4T and various nucleoside analogs was detected. The limit of quantitation of the method approximated 20 ng/ml. Replicate analyses of quality control samples (40 to 3,500 ng/ml) had satisfactory intra- and interassay precision (coefficient of variation, 1.7 to 16.7%) and accuracy (deviation, -9.5 to +21.0). This newly developed RIA was successfully used in the monitoring of plasma drug levels in healthy volunteers receiving an oral dose of D4T.

In vitro potency of inhibition by antiviral drugs of hematopoietic progenitor colony formation correlates with exposure at hemotoxic levels in human immunodeficiency virus-positive humans

Inhibition of in vitro colony formation of human hematopoietic progenitors (CFU-granulocyte-macrophage, burst-forming unit-erythroid) by the antiviral nucleoside drugs alovudine, zalcitabine, zidovudine, ganciclovir, stavudine, didanosine, lamivudine, and acyclovir was measured. Significant correlations between in vitro 50% inhibitory concentrations and the daily human exposures (area under the concentration-time curve from 0 to 24 h; in micromolar.hour) of these chronically administered drugs in human immunodeficiency virus-positive patients that induced neutropenia or anemia were demonstrated by both linear regression and Spearman rank-order analyses. These quantitative correlations allow estimation of the exposure at which bone marrow toxicity may occur with candidate compounds.

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.