Daniel S. Stein

A 24-week open-label phase I/II evaluation of the HIV protease inhibitor MK-639 (indinavir).

Objective:To investigate the safety, pharmacokinetics, and activity of the orally bioavailable protease inhibitor MK-639. Design:An open-label Phase I/II trial of medically stable subjects with screening CD4 lymphocyte counts ≤ 300×106/l and ≥ 20 000 HIV RNA copies/ml. Pharmacokinetics were performed at days 1 and 15. In order to better understand the relationships between drug exposure, baseline activity markers, and their changes during the study, mathematical modeling was performed using the traditional sigmoid-Emax relationship of pharmacologic effect and first order inhomogeneous differential equations for a two compartment system. Results:The five men enrolled had extensive prior nucleoside therapy (mean, 32.6 ± 25.6 months), a low mean CD4 lymphocyte cell count (CD4 count, 66.1 ± 61×106/l and CD4 percentage, 4.4 ± 3.1%), high soluble tumor necrosis factor-α type II (sTNFII) receptor concentration (6.23 ± 2.76 ng/ml) and high viral load (5.13 ± 0.46 log10 RNA copies/ml; geometric mean, 133 941 copies/ml). The drug was well tolerated at a dose of 600 mg every 6 h. The steady state concentrations Cmax and Cmin were 4.94 ± 2.16 μM and 0.28 ± 0.1 μM, respectively, which are ≈50 and 3 times the 95% inhibitory concentration (IC95) for clinical isolates, respectively. The mean increase in CD4 cell count was 143×106/l (217% increase), the mean increase in CD4 percentage was 5.2 percentage points (118%), mean decrease in HIV RNA was 1.55 log10 RNA copies/ml (a geometric mean difference of 130 120 copies/ml or 97% decrease) with a slow upward drift on continued therapy to a mean 0.64 log10 RNA copies/ml decrease by week 24 (a geometric mean difference of 103 084 copies/ml or 77% decrease), and a mean decrease in sTNFII receptors of 2.78 ng/ml (45% decrease). The mean CD4 counts per week as a function of the starting CD4 counts fit a sigmoid-Emax relationship (r2 = 0.998, P < 0.0001) with the return of CD4 cells being strongly related to the number of CD4 cells at baseline. Drug exposure as measured by either the total exposure (area under the concentration/time curve) or as the Cmin gave similar significant relationships to the fractional inhibition of HIV generation (r2 = 0.999, P < 0.0001, and r2 = 0.996, P < 0.0001, respectively). Conclusions:MK-639 appears to have significant dose-related antiviral activity and is well tolerated.

Zidovudine alone or in combination with didanosine or zalcitabine in HIV-infected patients with the acquired immunodeficiency syndrome or fewer than 200 CD4 cells per cubic millimeter

BACKGROUND We compared two combinations of nucleosides with zidovudine alone in patients with advanced human immunodeficiency virus (HIV) infection. METHODS A total of 1102 patients with the acquired immunodeficiency syndrome or fewer than 200 CD4 cells per cubic millimeter were randomly assigned to receive zidovudine alone or zidovudine combined with either didanosine or zalcitabine. Disease progression, survival, toxic effects, and the CD4 cell response were assessed. RESULTS After a median follow-up of 35 months, disease progression or death occurred in 62 percent of the 363 patients assigned to zidovudine plus didanosine, 63 percent of the 367 assigned to zidovudine plus zalcitabine, and 66 percent of the 372 assigned to zidovudine only (P=0.24). As compared with zidovudine therapy, treatment with zidovudine plus didanosine was associated with a relative risk of disease progression or death of 0.86 (95 percent confidence interval, 0.71 to 1.03), and treatment with zidovudine plus zalcitabine was associated with a relative risk of 0.92 (95 percent confidence interval, 0.76 to 1.10). Survival was similar in the three groups. In a subgroup analysis, combination therapy delayed disease progression or death in patients who had previously received zidovudine for 12 months or less. Therapy with zidovudine plus didanosine resulted in more gastrointestinal adverse effects, and treatment with zidovudine plus zalcitabine, more neuropathy. The mean increases in CD4 cell counts at two months were higher with combination therapy than with zidovudine alone. CONCLUSIONS In patients with advanced HIV infection, combination therapy with zidovudine and either didanosine or zalcitabine is not superior to zidovudine therapy alone. However, these combinations may be more effective than zidovudine monotherapy in patients with little or no previous zidovudine treatment.

A Comparison of Immediate with Deferred Zidovudine Therapy for Asymptomatic HIV-Infected Adults with CD4 Cell Counts of 500 or More per Cubic Millimeter

BACKGROUND The clinical benefits of zidovudine remain unproved in patients with asymptomatic human immunodeficiency virus (HIV) infection when CD4 cell counts exceed 500 per cubic millimeter. We compared zidovudine therapy given immediately with deferred therapy in such subjects. METHODS Beginning in 1987, subjects with asymptomatic HIV infection and 500 or more CD4 cells per cubic millimeter were randomly assigned to receive placebo or zidovudine (either 500 or 1500 mg per day, starting immediately). In 1989, the study was modified so that open-label treatment with 500 mg of zidovudine per day (deferred therapy) was offered when CD4 cell counts fell below 500 per cubic millimeter. The study end points included overall survival, survival free of the acquired immunodeficiency syndrome (AIDS), toxic effects, and changes in CD4 cell counts. RESULTS There were 1637 subjects who could be evaluated: 547 in the deferred-therapy group, 549 in the group receiving 500 mg of zidovudine immediately, and 541 in the 1500-mg group. The subjects were followed for up to 6.5 years (group medians, 4.8, 4.8, and 4.9, respectively). There was no significant difference in AIDS-free survival in the deferred-therapy group as compared with the low-dose or high-dose groups (81 cases of progression to AIDS or death vs. 81 and 74, respectively; P = 0.95 and P = 0.13) or in overall survival (51 deaths vs. 47 and 46; P = 0.25 and P = 0.16). The decline in CD4 cells was slower in both immediate-therapy groups than in the deferred-therapy group (P < 0.001 for both). Adverse effects were uncommon, and before the study modification their incidence was similar among the treatment groups, but severe anemia and granulocytopenia were more frequent in the 1500-mg group than in the deferred-therapy group (P < 0.001). CONCLUSIONS In asymptomatic, HIV-infected adults with 500 or more CD4 cells per cubic millimeter, treatment with zidovudine slows the decline in the CD4 cell count but does not significantly prolong either AIDS-free or overall survival. These results do not encourage the routine use of zidovudine monotherapy in this population.

Combination and Monotherapy with Zidovudine and Zalcitabine in Patients with Advanced HIV Disease

Several nucleoside analogs, including zidovudine, zalcitabine, and didanosine, inhibit the replication of human immunodeficiency virus type 1 (HIV) in vitro and improve CD4 cell counts and suppress HIV p24 antigenemia in patients with HIV disease [1-8]. Zidovudine therapy delays HIV disease progression [1-3] and improves survival in patients with advanced HIV disease [1, 9]. Didanosine therapy delays HIV disease progression in patients with advanced HIV disease who had previously received zidovudine, suggesting that switching antiretroviral therapy may be an important strategy in treating HIV disease [10, 11]. The combination of the nucleoside analogs zidovudine and zalcitabine has additive to synergistic inhibitory activity against HIV in vitro, and viral isolates resistant to zidovudine remain susceptible to zalcitabine in vitro [12-14]. Combination therapy with zidovudine and zalcitabine causes a greater and more sustained increase in CD4 cell counts and suppression of HIV p24 antigenemia than does either drug used alone in patients with advanced HIV disease who have not previously received therapy with zidovudine or zalcitabine [15]. The clinical correlation of these findings is unknown. These observations prompted us to try to determine whether zalcitabine monotherapy or combination therapy with zidovudine and zalcitabine would improve clinical outcome in patients with advanced HIV disease who had previously received zidovudine. Methods Study Sample The study sample consisted of patients with symptomatic HIV disease who had a CD4 cell count of 300 cells/mm3 or less or patients with asymptomatic HIV disease who had a CD4 cell count of 200 cells/mm3 or less. Participants had previously received and tolerated at least 6 months of zidovudine treatment. The eligibility criteria also included a hemoglobin concentration of 92 g/L or more, a neutrophil count of 1.0 109/L or more, a platelet count of 75 109/L or more, serum alanine aminotransferase and aspartate aminotransferase levels no higher than five times the upper range of normal, Karnofsky performance status of 60 or more, and positive results of serum tests for HIV antibody. We excluded patients with a history of intolerance to zidovudine at a dose of 600 mg/d or less, previous zalcitabine therapy, mild or more severe peripheral neuropathy, or Kaposi sarcoma requiring systemic therapy; women of childbearing age who were pregnant or breast-feeding were also excluded. We accepted patients receiving chemoprophylaxis for Pneumocystis carinii pneumonia, candidiasis and herpes simplex virus infection, and those receiving erythropoietin and granulocyte colony-stimulating factor. We excluded persons taking other antiretroviral drugs, biological response modifiers, cytotoxic chemotherapy, drugs other than isoniazid that cause peripheral neuropathy, or investigational drugs. We recruited patients from 35 AIDS Clinical Trials Units and 16 National Hemophilia Foundation sites between December 1990 and August 1991. The study was approved by the institutional review board at each institution, and patients gave written informed consent. Study Design and Treatment Regimen The study was a multicenter, randomized, double-blind clinical trial that compared the safety and efficacy of zidovudine, zalcitabine, and the combination of zidovudine and zalcitabine. Randomization was weighted at 2:2:3, favoring the combination group. Patients were stratified by HIV disease status (symptomatic or asymptomatic), by duration of previous zidovudine therapy ( 1 year or >1 year), and by P. carinii pneumonia chemoprophylaxis regimen (systemic therapy, nonsystemic therapy, both, or neither). Zalcitabine (Hivid; Hoffmann-La Roche, Inc., Nutley, New Jersey) was given in two 0.375-mg tablets every 8 hours. Zidovudine (Retrovir; Burroughs Wellcome Co., Research Triangle Park, North Carolina) was given in two 100-mg capsules every 8 hours. The primary end point for the study was time to an acquired immunodeficiency syndrome (AIDS)-defining event or death, whichever occurred first. All end points were reviewed in a blinded manner by the study chairpersons. Patients continued to receive blinded study medication after the development of a primary study end point. The protocol was modified on 20 March 1992 to allow patients who had reached a primary study end point the option to cross over to open-label combination therapy. Secondary end points included survival, CD4 cell count changes, and decreased HIV p24 antigenemia. Management of Toxic Effects All study medications were interrupted, regardless of whether the toxicity was believed to be associated with either zidovudine or zalcitabine, in patients in whom a moderate or severe peripheral neuropathy or another severe or worse toxic effect developed. Once the toxicity grade returned to pretreatment values or a lower grade, study medications were restarted at one half the initial dose. Study medications were permanently discontinued in patients who had a recurrent moderate or severe peripheral neuropathy or another severe or worse toxic effect within a 30-day period. Patients who had recurrent toxic effects after more than 30 days, except for those with peripheral neuropathy, continued to receive study medications once the toxicity grade returned to a lower grade or to pretreatment values. Patient Evaluation Patients were evaluated at weeks 0, 4, 8, and 12, and every 8 weeks thereafter. The CD4 cell counts were measured within 60 days before study enrollment, at weeks 0, 2, and 4, every 4 weeks until week 52, and every 8 weeks thereafter. Blood for HIV p24 antigen determinations was collected at weeks 0, 2, 4, 8, 12, 24, 36, 48, and 60 and every 16 weeks thereafter. Determinations of HIV p24 antigen were done simultaneously on stored serum aliquots by an enzyme-linked immunosorbent assay (Abbott Laboratories, North Chicago, Illinois). A positive assay result was one that detected an antigen level of 25 pg/mL or more. Laboratories measuring CD4 cell counts and serum p24 antigen levels had to meet the performance-monitored standards of the AIDS Clinical Trials Group. Statistical Analysis We assessed differences in proportions using the Fisher exact test. Time-to-event distributions were estimated using the Kaplan-Meier method and compared using the log-rank test and Cox proportional-hazards model [16], with stratification for HIV disease status, duration of previous zidovudine therapy, and P. carinii pneumonia prophylaxis [17]. Analyses were based on an intention-to-treat approach [18]. We censored data on toxic effects 30 days after crossover or discontinuation of study medications. We used the hazard ratios, expressed as relative risk, and 95% two-sided confidence intervals. All P values were two-sided and were not adjusted for multiple comparisons. A test of trend evaluating the interaction between pretreatment CD4 cell counts and treatment effect on the primary end point was based on Cox models and included the study stratification factors as covariates and pretreatment CD4 cell counts as a continuous variable. For completeness, two additional tests of trend used stratified Cox models in which pretreatment CD4 cell counts were modeled as a categorical variable. In one analysis, pretreatment CD4 cell count was modeled as a binary variable, above and below the median CD4 cell count (119 cells/mm3). In a second analysis, pretreatment CD4 cell count was modeled as a discrete variable with three levels ( 1,0, 1) corresponding to the three planned CD4 cell subgroups. Changes in CD4 cell counts and serum HIV p24 antigen levels were expressed as the percentage change from pretreatment values for each patient. Trends in CD4 cell counts over time were evaluated by estimating the slopes from pretreatment to the time of aggregate peak (week 2) and separately estimating the slopes for subsequent time points. We compared the slopes using nonparametric tests [19]. We also analyzed treatment differences for patients with pretreatment CD4 cell counts of less than 50 cells/mm3, 50 to 150 cells/mm3, and 150 cells/mm3 or greater. The three CD4 cell count subgroups were specified by the study chairpersons in June 1992, which was before any interim review of the primary end-point data and unblinding to the study results by the study chairpersons (March 1993). The three CD4 cell count subgroups were chosen based on documented associations between CD4 cell counts and survival and development of zidovudine resistance. Results Study Sample We enrolled 1001 patients in the study between December 1990 and August 1991. No patients were ineligible for the study, except for those granted an exemption by the study chairpersons. We excluded 10 patients from the analyses: 7 who never received study medications and were not followed and 3 who were lost to follow-up within the first 2 weeks of treatment. The patients included 888 (90%) men and 103 (10%) women; their median age was 37 years. Overall, 809 patients (82%) were white, 152 (15%) were black, and 3% were neither; 117 (12%) were Hispanic and 884 (88%) were non-Hispanic. Eight hundred nineteen (83%) patients had symptomatic HIV disease. The median duration of previous zidovudine therapy was 18 months. The median pretreatment CD4 cell count was 119 cells/mm3, and 254 of 925 patients had detectable levels of serum HIV p24 antigen ( 25 pg/mL) before treatment. The treatment groups were well balanced with regard to pretreatment characteristics (Table 1). Table 1. Patient Characteristics by Treatment Group* We randomly assigned 283 patients to the zidovudine group, 285 to the zalcitabine group, and 423 to the combination group. Three hundred eighty-six patients had 150 or more CD4 cells/mm3, 336 had 50 to 150 CD4 cells/mm3, and 269 had fewer than 50 CD4 cells/mm3. Overall, the treatment groups within each CD4 cell subgroup were well balanced with regard to pretreatment characteristics (data not shown). The median duration of foll

Pharmacokinetic and Pharmacodynamic Study of the Human Immunodeficiency Virus Protease Inhibitor Amprenavir after Multiple Oral Dosing

ABSTRACT In a dose-ranging study of amprenavir (formerly 141W94), an inhibitor of the protease enzyme of human immunodeficiency virus (HIV) type 1, single-dose and steady-state pharmacokinetic parameters were estimated from plasma samples collected on day 1 and during week 3, respectively. Amprenavir was administered on either a twice-daily (b.i.d.) or three-times-daily dosage schedule to 62 HIV-infected adults, 59 of whom had pharmacokinetic data. Log-log regression analysis (the power model) revealed that the steady-state area under the curve (AUCss) and the maximum, minimum, and average concentrations at steady state (Cmax,ss,Cmin,ss, and Cavg,ss, respectively) increased in a dose-proportional manner over the 300- to 1,200-mg dose range. Steady-state clearance was dose independent. AUCss/AUC0→∞ decreased linearly with dose and correlated significantly with treatment-associated decreases in α1-acid glycoprotein. After 3 weeks, the dose of 1,200 mg b.i.d. provided a median amprenavir Cmin,ss (0.280 μg/ml) that was higher than the median in vitro 50% inhibitory concentration for clinical HIV isolates (0.023 μg/ml), even after adjustment for protein binding. The median amprenavir Cmin,sswas also greater than the estimated in vivo trough concentration calculated to yield 90% of the maximum antiviral effect (0.228 μg/ml) over 4 weeks. A pharmacodynamic analysis of the relationship between steady-state pharmacokinetic parameters and safety revealed headache and oral numbness to be the only side effects significantly associated with Cmax. The pharmacodynamic relationship defined in this study supports the use of 1,200 mg b.i.d. as the approved dose of amprenavir.

Phase I/II evaluation of nevirapine alone and in combination with zidovudine for infection with human immunodeficiency virus

In these Phase I/II open-label clinical trials, 62 persons with human immunodeficiency virus type 1 (HIV-1) infection and CD4+ cell counts < 400/mm3 received nevirapine at doses of 12.5, 50, and 200 mg/day, alone or in combination with zidovudine, 200 mg q8h. Nevirapine was well tolerated in the doses tested. Mean steady-state trough levels were 0.23, 1.1, and 1.9 micrograms/ml for the 12.5, 50, and 200 mg/day doses, respectively. Early suppression of p24 antigen levels and increase in CD4+ cell count were reversed following rapid emergence of virus less susceptible to nevirapine. Resistant strains were isolated from all participants by 8 weeks. Nevertheless, reduction of p24 antigen levels to < 50% of baseline values persisted for 12 weeks or more in four of seven persons who received 200 mg nevirapine/day in combination with zidovudine: these individuals had been antigenemic on long-term zidovudine therapy. This study demonstrates a direct relationship between drug resistance and effects on surrogate markers in HIV-1 infection.

Pharmacokinetics and safety of amprenavir and ritonavir following multiple-dose, co-administration to healthy volunteers.

ObjectiveTo evaluate the safety and pharmacokinetic interaction between amprenavir (APV) and ritonavir (RTV). MethodsThree open-label, randomized, two-sequence, multiple-dose studies having the same design (7 days of APV or RTV alone followed by 7 days of both drugs together) used 450 or 900 mg APV with 100 or 300 mg RTV every 12 h with pharmacokinetic assessments on days 7 and 14. Safety was monitored as clinical adverse events (AEs) and laboratory abnormalities. ResultsRelative to APV alone, RTV co-administration resulted in a 3.3- to 4-fold and 10.84 to 14.25-fold increase in the geometric least-square (GLS) mean area under the plasma concentration–time curve (AUCτ,ss) and minimum concentration (Cmin,ss), respectively. APV 900 mg with RTV 100 mg resulted in a 2.09-fold and 6.85-fold increase in the GLS mean AUCτ,ss and Cmin,ss, respectively. On day 14, the geometric mean (95% confidence interval) for 450 mg APV AUCτ,ss (μg • h/mL) was 23.49 (19.32–28.57) with 300 mg RTV and 35.42 (30.46–44.42) with 100 μg RTV, and for the 900 mg APV with 100 mg RTV 47.11 (39.47–61.24). The 450 mg APV Cmin,ss (μg/ml) were 1.32 (1.05–1.67) and 2.01 (1.70–2.61), and 2.47 (2.08–3.32) for 900 mg APV. The most common AEs were mild and included diarrhea, nausea/vomiting, oral parasthesias, and rash. The triglyceride and cholesterol increased significantly from RTV exposure. ConclusionAdding RTV to APV resulted in clinically and statistically significant increases in APV AUC and Cmin with variable effects on maximum concentration. The two RTV doses had similar effects on APV but AEs were more frequent with 300 mg RTV.

Single-Dose Pharmacokinetics of Amprenavir, a Human Immunodeficiency Virus Type 1 Protease Inhibitor, in Subjects with Normal or Impaired Hepatic Function

ABSTRACT Amprenavir (141W94) is extensively metabolized by P450 cytochromes, specifically, CYP3A4. Because hepatic insufficiency reduces P450-mediated metabolism, the concentrations in plasma of drugs metabolized through this pathway are often increased in subjects with liver disease. Following administration of a single, oral dose of 600 mg of amprenavir, pharmacokinetic parameters were determined for 10 subjects with severe cirrhosis, 10 subjects with moderate cirrhosis, and 10 healthy volunteers. Model-independent methods for determining the area under the plasma concentration-time curve (AUC) from time zero to infinity (AUC0–∞) showed an increase in amprenavir AUC0–∞ of 2.5-fold in the group with moderate cirrhosis and 4.5-fold in the group with severe cirrhosis compared with that in the control group of healthy volunteers (P < 0.05). AUC0–∞ was linearly related to the severity of liver disease, as assessed by the Child-Pugh score. Of the laboratory data used to calculate the Child-Pugh score, only the mean total bilirubin concentration showed a significant relationship with AUC0–∞. The relationship between the total bilirubin concentration and the AUC0–∞ of amprenavir was well characterized by a simple Emax model, suggesting that the total bilirubin concentration may be a useful parameter for predicting the amprenavir AUC in subjects with hepatic insufficiency. Finally, the sera of cirrhotic subjects showed significant decreases in the levels of α1-acid glycoprotein, the primary plasma binding protein for amprenavir. On the basis of the results of this study, for an exposure equivalent to a clinical dose of 1,200 mg twice daily in subjects without cirrhosis, subjects with Child-Pugh scores of 5 to 8 should receive a twice-daily 450-mg dose of amprenavir, and subjects with Child-Pugh scores of 9 to 15 should receive a twice-daily 300-mg dose of amprenavir.

Population Pharmacokinetics and Pharmacodynamic Modeling of Abacavir (1592U89) from a Dose-Ranging, Double-Blind, Randomized Monotherapy Trial with Human Immunodeficiency Virus-Infected Subjects

ABSTRACT Abacavir (formerly 1592U89) is a carbocyclic nucleoside analog with potent anti-human immunodeficiency virus (anti-HIV) activity when administered alone or in combination with other antiretroviral agents. The population pharmacokinetics and pharmacodynamics of abacavir were investigated in 41 HIV type 1 (HIV-1)-infected, antiretroviral naive adults with baseline CD4+ cell counts of ≥100/mm3 and plasma HIV-1 RNA levels of >30,000 copies/ml. Data for analysis were obtained from patients who received randomized, blinded monotherapy with abacavir at 100, 300, or 600 mg twice-daily (BID) for up to 12 weeks. Plasma abacavir concentrations from sparse sampling were analyzed by standard population pharmacokinetic methods, and the effects of dose, combination therapy, gender, weight, and age on parameter estimates were investigated. Bayesian pharmacokinetic parameter estimates were calculated to determine the peak concentration of abacavir in plasma (Cmax) and the area under the concentration-time curve from time zero to infinity (AUC0–∞) for individual subjects. The pharmacokinetics of abacavir were dose proportional over the 100- to 600-mg dose range and were unaffected by any covariates. No significant correlations were observed between the incidence of the five most common adverse events (headache, nausea, diarrhea, vomiting, and malaise or fatigue) and AUC0–∞. A significant correlation was observed betweenCmax and nausea by categorical analysis (P = 0.019), but this was of borderline significance by logistic regression (odds ratio, 1.45; 95% confidence interval, 0.95 to 2.32). The log10 time-averaged AUC0–∞ minus baseline (AAUCMB) values for HIV-1 RNA and CD4+ cell count correlated significantly withCmax and AUC0–∞, but with better model fits for AUC0–∞. The increase in AAUCMB values for CD4+ cell count plateaued early for drug exposures that were associated with little change in AAUCMB values for plasma HIV-1 RNA. There was less than a 0.4 log10 difference over 12 weeks in the HIV-1 RNA levels with the doubling of the abacavir AUC0–∞ from 300 to 600 mg BID dosing. In conclusion, pharmacodynamic modeling supports the selection of abacavir 300 mg twice-daily dosing.

Phase I Studies of Hypericin, the Active Compound in St. John's Wort, as an Antiretroviral Agent in HIV-Infected Adults: AIDS Clinical Trials Group Protocols 150 and 258

Hypericin, the active compound in St. Johns wort, caused significant phototoxicity and had no antiretroviral activity in HIV-infected patients.