A randomized pilot study of alternating or simultaneous zidovudine and didanosine therapy in patients with symptomatic human immunodeficiency virus infection

Twenty-Five Years of Lamivudine: Current and Future Use for the Treatment of HIV-1 Infection

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Innovation in medicine is a dynamic, complex, and continuous process that cannot be isolated to a single moment in time. Anniversaries offer opportunities to commemorate crucial discoveries of modern medicine, such as penicillin (1928), polio vaccination (inactivated, 1955; oral, 1961), the surface antigen of the hepatitis B virus (1967), monoclonal antibodies (1975), and the first HIV antiretroviral drugs (zidovudine, 1987). The advent of antiretroviral drugs has had a profound effect on the progress of the epidemiology of HIV infection, transforming a terminal, irreversible disease that caused a global health crisis into a treatable but chronic disease. This result has been driven by the success of antiretroviral drug combinations that include nucleoside reverse transcriptase inhibitors such as lamivudine. Lamivudine, an L-enantiomeric analog of cytosine, potently affects HIV replication by inhibiting viral reverse transcriptase enzymes at concentrations without toxicity against human polymerases. Although lamivudine was approved more than 2 decades ago, it remains a key component of first-line therapy for HIV because of its virological efficacy and ability to be partnered with other antiretroviral agents in traditional and novel combination therapies. The prominence of lamivudine in HIV therapy is highlighted by its incorporation in recent innovative treatment strategies, such as single-tablet regimens that address challenges associated with regimen complexity and treatment adherence and 2-drug regimens being developed to mitigate cumulative drug exposure and toxicities. This review summarizes how the pharmacologic and virologic properties of lamivudine have solidified its role in contemporary HIV therapy and continue to support its use in emerging therapies.

Recent Progress in the Development of HIV-1 Protease Inhibitors for the Treatment of HIV/AIDS

HIV-1 protease inhibitors continue to play an important role in the treatment of HIV/AIDS, transforming this deadly ailment into a more manageable chronic infection. Over the years, intensive research has led to a variety of approved protease inhibitors for the treatment of HIV/AIDS. In this review, we outline current drug design and medicinal chemistry efforts toward the development of next-generation protease inhibitors beyond the currently approved drugs.

N348I in reverse transcriptase provides a genetic pathway for HIV-1 to select thymidine analogue mutations and mutations antagonistic to thymidine analogue mutations

OBJECTIVE

Several nonnucleoside (e.g. Y181C) and nucleoside (e.g. L74V and M184V) resistance mutations in HIV-1 reverse transcriptase are antagonistic toward thymidine analogue mutations (TAMs) that confer zidovudine (ZDV) resistance. The N348I mutation in the connection domain of reverse transcriptase also confers ZDV resistance; however, the mechanisms involved are different from TAMs. In this study, we examined whether N348I compensates for the antagonism of the TAM K70R by Y181C, L74V and M184V.

DESIGN AND METHODS

The ZDV monophosphate and ribonuclease H activities of recombinant-purified HIV-1 reverse transcriptase-containing combinations of K70R, N348I and Y181C, L74V or M184V were assessed using standard biochemical and antiviral assays.

RESULTS

As expected, the introduction of the Y181C, L74V or M184V mutations into K70R HIV-1 reverse transcriptase significantly diminished the ATP-mediated ZDV monophosphate excision activity of the enzyme. However, the N348I mutation compensated for this antagonism on RNA/DNA template/primers by significantly decreasing the frequency of secondary ribonuclease H cleavages that reduce the overall efficiency of the excision reaction.

CONCLUSION

The acquisition of N348I in HIV-1 reverse transcriptase - which can occur early in therapy, oftentimes before TAMs - may provide a simple genetic pathway that allows the virus to select both TAMs and mutations that are antagonistic toward TAMs.

The triple combination of tenofovir, emtricitabine and efavirenz shows synergistic anti-HIV-1 activity in vitro: a mechanism of action study

Background

Tenofovir disoproxil fumarate (TDF), emtricitabine (FTC), and efavirenz (EFV) are the three components of the once-daily, single tablet regimen (Atripla) for treatment of HIV-1 infection. Previous cell culture studies have demonstrated that the double combination of tenofovir (TFV), the parent drug of TDF, and FTC were additive to synergistic in their anti-HIV activity, which correlated with increased levels of intracellular phosphorylation of both compounds.

Results

In this study, we demonstrated the combinations of TFV+FTC, TFV+EFV, FTC+EFV, and TFV+FTC+EFV synergistically inhibit HIV replication in cell culture and synergistically inhibit HIV-1 reverse transcriptase (RT) catalyzed DNA synthesis in biochemical assays. Several different methods were applied to define synergy including median-effect analysis, MacSynergy^®II and quantitative isobologram analysis. We demonstrated that the enhanced formation of dead-end complexes (DEC) by HIV-1 RT and TFV-terminated DNA in the presence of FTC-triphosphate (TP) could contribute to the synergy observed for the combination of TFV+FTC, possibly through reduced terminal NRTI excision. Furthermore, we showed that EFV facilitated efficient formation of stable, DEC-like complexes by TFV- or FTC-monophosphate (MP)-terminated DNA and this can contribute to the synergistic inhibition of HIV-1 RT by TFV-diphosphate (DP)+EFV and FTC-TP+EFV combinations.

Conclusion

This study demonstrated a clear correlation between the synergistic antiviral activities of TFV+FTC, TFV+EFV, FTC+EFV, and TFV+FTC+EFV combinations and synergistic HIV-1 RT inhibition at the enzymatic level. We propose the molecular mechanisms for the TFV+FTC+EFV synergy to be a combination of increased levels of the active metabolites TFV-DP and FTC-TP and enhanced DEC formation by a chain-terminated DNA and HIV-1 RT in the presence of the second and the third drug in the combination. This study furthers the understanding of the longstanding observations of synergistic anti-HIV-1 effects of many NRTI+NNRTI and certain NRTI+NRTI combinations in cell culture, and provides biochemical evidence that combinations of anti-HIV agents can increase the intracellular drug efficacy, without increasing the extracellular drug concentrations.

Obesity among patients with HIV: the latest epidemic

Since the advent of highly active antiretroviral therapy (HAART), studies have been conflicting regarding weight information among patients with HIV. We performed a retrospective study among male patients with HIV between June 2004 and June 2005 at two large U.S. Navy HIV clinics to describe the prevalence and factors associated with being overweight/obese. Rates of obesity/overweight among HIV-positive patients were also compared to data from HIV-negative military personnel. Of the 661 HIV-infected patients, 419 (63%) were overweight/obese and only 5 (1%) were underweight. Patients with HIV had a mean age of 41.0 years (range, 20-73 years) and were racially diverse. The prevalence rates of being overweight/obese at the last visit were similar among both HIV-positive and -negative military members. Being overweight/obese at the last clinic visit was associated with gaining weight during the course of HIV infection (10.4 versus 4.0 pounds, p < 0.001), hypertension (36% versus 23%, p = 0.001), low high-density lipoprotein (HDL; 40% versus 31%, p < 0.001), and a higher CD4 cell count at last visit (592 versus 499 cells/mm(3), p < 0.001). These data demonstrate that patients with HIV in the HAART era are commonly overweight and/or obese with rates similar to the general population. Being overweight/obese is associated with hypertension and dyslipidemia. Weight assessment and management programs should be a part of routine HIV clinical care.

Hyperlactataemia and lactic acidosis in HIV-infected patients receiving antiretroviral therapy

Nucleoside reverse-transcriptase inhibitors (NRTIs) have been associated with functional and structural mitochondrial abnormalities, leading to several adverse events, such as increased serum lactic acid levels and lactic acidosis. Mild-to-moderate, asymptomatic hyperlactataemia has been frequently reported in human immunodeficiency virus (HIV)-infected patients treated with NRTIs, with an estimated prevalence between 15% and 35%. On the contrary, symptomatic, severe hyperlactataemia and lactic acidosis are less common, with an incidence ranging from 1.7 to 25.2 cases per 1000 person-years of antiretroviral treatment, and are associated with a remarkable mortality rate, which varies from 30% to 60% in different studies. The clinical presentation of lactic acid syndrome is non-specific and includes asthenia, malaise, nausea, vomiting, abdominal pain, weight loss, tachypnoea, dyspnoea, liver steatosis and increased transaminase levels, and risk factors include previous or concurrent therapy with stavudine or didanosine. Management of symptomatic lactic acid alterations involves NRTI-therapy interruption and supportive care, while natural history of hyperlactataemia is still unknown, and it is uncertain whether asymptomatic patients with increased lactate concentrations are at increased risk of developing lactic acidosis.

Selected metabolic and morphologic complications associated with highly active antiretroviral therapy

Metabolic and morphologic changes have been described in patients with human immunodeficiency virus (HIV) infection. In the short term, these disorders can be debilitating and may require medical intervention, including alterations in antiretroviral therapy regimens. The long-term consequences have not been fully realized, but are important, particularly in the era of durable HIV disease management with highly active antiretroviral therapy. This review focuses on 3 of the important morphologic or metabolic changes, namely alterations in body fat distribution, dyslipidemia, and lactic acidosis. The prevalence of each of these disorders remains unknown due to varied definitions and difficulty in recognition of the conditions for both the patient and the clinician. Treatment regimens directed at these abnormalities are being developed, but clinical trials are needed to fully ascertain the efficacy and safety of such interventions.

Systematic review and meta-analysis of evidence for increasing numbers of drugs in antiretroviral combination therapy

OBJECTIVE

To assess the evidence for the effectiveness of increasing numbers of drugs in antiretroviral combination therapy.

DESIGN

Systematic review, meta-analysis, and meta-regression of fully reported randomised controlled trials. All studies included compared quadruple versus triple therapy, triple versus double therapy, double versus monotherapy, or monotherapy versus placebo or no treatment.

PARTICIPANTS

Patients with any stage of HIV infection who had not received antiretroviral therapy.

MAIN OUTCOME MEASURES

Changes in disease progression or death (clinical outcomes); CD4 count and plasma viral load (surrogate markers).

SEARCH STRATEGY

Six electronic databases, including Medline, Embase, and the Cochrane Library, searched up to February 2001.

RESULTS

54 randomised controlled trials, most of good quality, with 66 comparison groups were included in the analysis. For both the clinical outcomes and surrogate markers, combinations with up to and including three (triple therapy) were progressively and significantly more effective. The odds ratio for disease progression or death for triple therapy compared with double therapy was 0.6 (95% confidence interval 0.5 to 0.8). Heterogeneity in effect sizes was present in many outcomes but was largely related to the drugs used and trial quality.

CONCLUSIONS

Evidence from randomised controlled trials supports the use of triple therapy. Research is needed on the effectiveness of quadruple therapies and the relative effectiveness of specific combinations of drugs.

Pharmacokinetic and other drug interactions in patients with AIDS

A variety of medications are used in treating patients infected with the human immunodeficiency virus (HIV). These medications are used to control viremia and to prevent and treat opportunistic infections. An individual is often required to take numerous drugs at the same time and thus clinicians are confronted with potential drug interactions, some of which are significant. Three different groups of anti-HIV drugs are used to treat patients. These groups include nucleoside reverse transcription inhibitors, non-nucleoside reverse transcription inhibitors, and protease inhibitors. This article reviews the most relevant drug interactions that occur during the treatment of HIV-infected patients with traditional and also alternative drugs. The role of therapeutic drug monitoring in the routine management of HIV-infected patients is discussed.

Evolution of AZT resistance in HIV-1: the 41-70 intermediate that is not observed in vivo has a replication defect

The human immunodeficiency virus type 1 (HIV-1) is notorious for its ability to evolve drug-resistance in patients treated with potent antivirals. Resistance to inhibitors of the viral reverse transcriptase (RT) enzyme is frequently mediated by a single amino acid substitution within RT. Resistance against the nucleoside analogue AZT is remarkable in that multiple amino acid changes accumulate over time to yield virus variants with high-level drug resistance. We now report that in addition to drug-resistance properties, the relative replication capacity of the virus variants affects the evolution of AZT resistance. Some of the typical AZT-resistance mutations have a negative impact on virus replication, and the 41-70 double mutant was found to represent a particularly poor virus. Furthermore, introduction of additional AZT-resistance mutations (41-70-215) leads to nearly complete restoration of virus replication. These results may explain the absence of the 41-70 double mutant in clinical samples and indicate that the evolution of AZT resistance is also influenced by virus replication parameters. Prolonged passage of the replication-impaired 41-70 virus in the absence of AZT yielded several fast-replicating variants. These revertants have compensatory changes in the RT polymerase, some of which have been observed previously in AZT-treated patients. Because we could select for these changes without drug pressure, these changes are likely to improve the RT enzyme function and the HIV-1 replication capacity.

International perspectives on antiretroviral resistance. Nucleoside reverse transcriptase inhibitor resistance

Nucleoside reverse transcriptase inhibitors (NRTIs) comprise the first class of drug with proven antiretroviral efficacy against HIV-1, and the first in which drug resistance was reported. Ongoing research in the area of NRTI resistance and cross-resistance contributes much to what we know about the failure of antiretroviral therapy. The genetic mutation patterns responsible for resistance to the available NRTIs have been well documented. This information is being used to plan rational drug therapy. Furthermore, it serves as the standard against which to evaluate response patterns to multiple-drug regimens, ultimately enabling more accurate prediction of outcome with combination therapies. Other features of NRTI resistance, such as the theoretic reversal of zidovudine resistance associated with the M184V mutation or the powerful influence of the Q151M multiple-drug resistance mutation, have revealed the unpredictable nature of HIV resistance and how much we still need to learn. Although NRTIs are the cornerstone of antiretroviral therapy at present and are used to control disease progression for extended periods, it is clear that eventually resistance occurs with all antiretroviral regimens. Future research into NRTI-resistance mutations, mutational interactions, treatment sequencing, and viral fitness and fidelity will continue to refine our understanding of drug resistance and improve our ability to delay or eliminate resistance and advance HIV control.

Didanosine once daily: potential for expanded use

Factors affecting patient adherence to therapy, such as frequent daily dosing and complex dosing schedules, are widely understood to be key obstacles to the durability of effective anti-HIV therapy. Didanosine, a nucleoside analogue reverse transcriptase inhibitor (NRTI) that is a core component of combination antiretroviral regimens, is currently indicated for twice-daily dosing. However, the active metabolite of didanosine (2',3'-dideoxyadenosine-5'-triphosphate) has a long intracellular half-life that supports the use of didanosine in a more patient-friendly, once-daily dosing schedule. Clinical studies in which didanosine was administered either once or twice daily, as monotherapy or in combination with another NRTI, have demonstrated the equivalence of both dosing schedules, with respect to safety and tolerability, virologic and immunologic endpoints, and short-term clinical effects (e.g., weight gain). Preliminary results from recent studies support the clinical efficacy and utility of once-daily didanosine in combination antiretroviral regimens that provide maximal drug exposure, while allowing for once- or twice-daily dosing of all component drugs.

Pharmacology of nucleoside and nucleotide reverse transcriptase inhibitor-induced mitochondrial toxicity

OBJECTIVE

This paper reviews the function of the mitochondria and the mechanisms by which nucleoside and nucleotide reverse transcriptase inhibitors (NRTIs) cause mitochondrial toxicity.

BACKGROUND

Highly active antiretroviral therapy (HAART) reduces rates of morbidity and mortality due to HIV disease. However, long-term treatment with these drugs may be associated with adverse effects. Nucleoside and nucleotide analogues are potent inhibitors of HIV reverse transcriptase and have become the cornerstone of HAART. Unfortunately, these drugs have also been shown to inhibit cellular polymerases, most notably mitochondrial DNA polymerase gamma.

RESULTS

Studies of the NRTIs in enzyme assays and cell cultures demonstrate the following hierarchy of mitochondrial DNA polymerase gamma inhibition: zalcitabine > didanosine > stavudine > lamivudine > zidovudine > abacavir. In vitro investigations have also documented impairment of the mitochondrial enzymes adenylate kinase and the adenosine diphosphate/adenosine triphosphate translocator. Inhibition of DNA polymerase gamma and other mitochondrial enzymes can gradually lead to mitochondrial dysfunction and cellular toxicity. The clinical manifestations of NRTI-induced mitochondrial toxicity resemble those of inherited mitochondrial diseases (ie, hepatic steatosis, lactic acidosis, myopathy, nephrotoxicity, peripheral neuropathy, and pancreatitis). Fat redistribution syndrome, or HIV-associated lipodystrophy, is another side effect attributed in part to NRTI therapy. The morphologic and metabolic complications of this syndrome are similar to those of the mitochondrial disorder known as multiple symmetric lipomatosis: suggesting that this too may be related to mitochondrial toxicity. The pathophysiology of less common adverse effects of nucleoside analogue therapy, such as diabetes, ototoxicity, and retinal lesions, may be related to mitochondrial dysfunction but have not been adequately studied.

CONCLUSION

NRTls can block both HIV reverse transcriptase and mitochondrial DNA polymerase gamma. Inhibition of the latter enzyme is the most likely cause of the adverse effects associated with these drugs.

Body weight changes with protease inhibitor treatment in undernourished HIV-infected patients

Effective reduction of HIV replication by protease inhibitor (PI) treatment was expected to reverse some of the weight loss associated with HIV infection. Body weight changes in undernourished HIV-infected patients starting PI treatment were compared to its virologic and immunologic effects. This was designed as a retrospective study using prospectively collected weight data; the setting was the HIV outpatient department of a university hospital. Among 223 consecutive HIV-positive patients starting treatment with PI February 1996 to September 1997, 63 undernourished patients were evaluable. The main outcome measures were weight trend, calculated by linear regression of a patient's weight versus time, and its change from a 4-14-wk baseline period to the first 14 wk, and 28 wk, after treatment. In our results, weight trend remained unchanged (baseline, +0.4 +/- 4.0 kg/100 d; 14 wk, +0.7 +/- 4.1 kg/100 d, and 28 wk, +1.0 +/- 3.4 kg/100 d, n.s.). Reduction of viremia and increase in CD4 cell count were unrelated to weight trends. Treatment with PI did not result in an improved weight trend. Altered body composition with PI treatment, as observed in other studies, does not seem to result in body weight changes. Drug side effects may have counteracted any positive effects. The metabolic and nutritional impact of effective antiviral treatment merits further study.

A trial comparing nucleoside monotherapy with sequential therapy with 3 drugs in HIV-infected patients

53 HIV-positive patients, 66% of them zidovudine-experienced, were randomized to receive monotherapy with zidovudine or sequential therapy with zidovudine, didanosine and zalcitabine. Clinical end points, CD4 cell count change, and analysis abnormalities showed better results with sequential therapy.

The effect of protease inhibitors on weight and body composition in HIV-infected patients

OBJECTIVES

To determine the nutritional changes that occur in HIV-infected patients receiving protease inhibitor (PI) therapy and to determine the effects of PI treatment on physical functioning and health perceptions in patients with HIV infection.

DESIGN

Longitudinal data analysis of 38 patients from a large Nutrition and HIV cohort.

METHODS

Patients were included if they had started PI therapy after enrollment in the cohort, if they had taken the drug for at least 4 months without interruption and if data on weight, body composition and viral loads were available.

RESULTS

Mean person-months of follow-up was 8.1 months before and 12.2 months after PI treatment. Weight (1.54 kg, P < 0.0001), body mass index (0.50 kg/m2, P < 0.0001), physical functioning (8.52 points, P = 0.0006) and current health perception (6.7 points, P = 0.01) increased significantly, and the daily caloric intake increase was close to significance (915.5 kJ/day, P = 0.06), after treatment with PI. Lean body mass did not change. Patients who responded to PI therapy with decreased viral load (n = 28) had significantly greater weight gain per month than non-responders.

CONCLUSIONS

PI therapy of HIV infection is associated with weight gain and improvement in quality of life indices. The weight gain is mainly in fat mass, with no change in lean body mass (skeletal muscle). Optimal therapy of HIV-infected patients with weight loss may require highly active antiretroviral therapy combined with an anabolic stimulus such as exercise, anabolic steroids or human growth hormone.

Loss of Lamivudine Resistance in a Zidovudine and Lamivudine Dual-Resistant HIV-1 Isolate after Discontinuation of In Vitro Lamivudine Drug Pressure

We examined the in vitro phenotypic and genotypic profiles of an extensively passaged human immunodeficiency virus type 1 clinical isolate which has been selected for lamivudine resistance, with an M184V mutation in a zidovudine-resistant genetic background, and then cultured with zidovudine alone. Our passaging strategy led to a decrease in lamivudine IC50 values, which were comparable to those prior to lamivudine exposure, and the genotypic restoration of the wild-type sequence at codon 184 of reverse transcriptase.

Inhibition of murine AIDS by a new azidothymidine homodinucleotide

A new antiretroviral drug (azidothymidine homodinucleotide, AZTp2AZT), designed for the protection of macrophages against retroviral infection, was evaluated in a murine retrovirus-induced immunodeficiency model of AIDS (MAIDS) alone and in combination with oral azidothymidine (AZT). C57BL/6 mice were infected with the retroviral complex LP-BM5 and treated for 3 months by weekly administrations of 15 nmol of AZTp2AZT encapsulated into autologous erythrocytes for macrophage protection. AZTp2AZT treatment was found to reduce lymphoadenopathy (48%), splenomegaly (26%), and BM5d proviral DNA content in lymph nodes, spleen, and brain of 37%, 40%, and 36%, respectively, compared with untreated animals. AZT administration in drinking water (0.25 mg/ml) was more effective than administration of AZTp2AZT encapsulated into erythrocytes in reducing lymphoadenopathy, splenomegaly, gammaglobulinemia, and proviral DNA content in lymph nodes, but it caused a reduction in erythrocyte count and hematocrit levels. Although combined treatments do not provide additive responses in the several parameters investigated, they were found to be much more effective in reducing the proviral DNA content in brain (67%) than were monotherapies. Furthermore, no apparent signs of hematotoxicity were observed. Thus, macrophage delivery of antiviral drugs may contribute to brain protection from retroviral infections by mechanisms other than those exerted by oral AZT administration.

Chemotherapeutic agents for human immunodeficiency virus infection: mechanism of action, pharmacokinetics, metabolism, and adverse reactions

Since the mid-1980s, four new nucleoside reverse transcriptase (RT) inhibitors (zalcitabine, didanosine, stavudine, and lamivudine), two nonnucleoside RT inhibitors (nevirapine and delavirdine), and four new protease inhibitors (saquinavir, ritonavir, indinavir, and nelfinavir) have been approved by the US Food and Drug Administration for the treatment of patients with acquired immunodeficiency syndrome. The driving force behind the development of these new agents has been the increasing need for more potent agents with reduced or modified toxicity profiles. The purpose of this article is to review the absorption, distribution, metabolism, elimination, toxicities, adverse reactions, and mechanism of action of the currently available drugs.

HIV-1 acquires resistance to two classes of antiviral drugs through homologous recombination

Genetic recombination contributes to the genomic heterogeneity of human immunodeficiency virus type 1 (HIV-1). In the present study, we demonstrate that HIV-1 readily develops resistance to two classes of anti-HIV-1 drugs through in vitro genetic recombination involving large segments of the viral genome. Co-transfection of COS-7 cells with an HIV-1 plasmid (pSUM13) carrying five mutations in the reverse transcriptase (RT)-encoding region (A62V, V75I, F77L, F116Y, Q151M), conferring resistance to multiple dideoxynucleoside analogs (ddNs), and another HIV-1 plasmid (pSUM431) carrying five mutations in the protease-encoding region (V321, L33F, K451, 184V, L89M), conferring resistance to protease inhibitors such as KNI-272, readily produced HIV-1 carrying both sets of mutations when propagated in MT-2 cells in the presence of azidothymidine (AZT) and KNI-272. The resultant HIV-1 variant was highly resistant to both ddNs and KNI-272. Co-infection of MT-2 cells with HIV-1SUM13 carrying the RT mutations and HIV-1SUM431 carrying the mutations in the protease also generated HIV-1 with both sets of mutations when cultured with AZT and KNI-272. We also report here that the problematic artifactual recombination occurring during genetic analyses of heterogeneous nucleic acid sequences using polymerase chain reaction can be successfully obviated.

Antiretroviral effect of combined zidovudine and reduced glutathione therapy in murine AIDS

A combination of antiretroviral drugs acting at different points in the virus replication cycle was evaluated in a murine retrovirus-induced immunodeficiency model of AIDS (MAIDS). Intramuscular administration of high doses of reduced glutathione (GSH, 100 mg/mouse/day) and AZT (0.25 mg/ml in drinking water) was found to reduce lymphoadenopathy (92%), splenomegaly (80%), and hypergammaglobulinemia (90%) significantly more than AZT alone. Combined treatment resulted in a reduction in proviral DNA content of 69, 66, and 60%, respectively, in lymph nodes, spleen, and bone marrow. Furthermore, the stimulation index of B cells was also significantly higher in animals receiving GSH and AZT whereas additional responses were not observed in the T cell stimulation index and blood lymphocyte phenotype analyses. In conclusion, the administration of high doses of GSH and AZT, a new combination of antiviral drugs, seems to provide additional advantages compared to single-agent therapy.

The pancreas in AIDS

Although autopsy studies reveal significant pancreatic lesions in about 10% of AIDS patients, pancreatic lesions infrequently produce symptoms and are rarely recognized premortem. Patients with AIDS can develop pancreatic disease from causes not related to AIDS or AIDS-specific lesions. AIDS-specific causes include opportunistic infection, AIDS-associated neoplasia, and medications used to treat complications of AIDS. Pancreatic involvement is usually part of a widely disseminated tumor and rarely produces clinical symptoms.

Current problems and the future of antiretroviral drug trials

Now that a growing arsenal of new and potential anti-HIV drugs exists, debate and discussion about the optimal way to test and use these drugs has begun. In his Policy Forum, Joep Lange, director of the National AIDS Therapy Evaluation Centre in Amsterdam, takes the controversial stand that suboptimal therapies and drug trial designs are still being used. He discusses the underlying reasons for this situation and the challenges for the future.

Antiviral efficacy and toxicity of ribavirin and foscarnet each given alone or in combination in the murine AIDS model

The antiviral efficacy and toxicity of ribavirin, foscarnet (PFA), and combinations of both drugs at two different doses have been evaluated in the murine AIDS (MAIDS) model. Our results clearly demonstrated that infected mice treated with ribavirin at 100 mg/ kg/day were protected against splenomegaly, lymphadenopathy, and hypergammaglobulinemia whereas PFA alone at 180 or 360 mg/kg/day did not afford any protection. Treatment with drug combinations showed protective effects similar to those observed with ribavirin alone. Hyperplasia and deorganization of the lymphoid architecture were noted in spleen and lymph nodes of infected mice compared to those of the uninfected group. However, treatment with ribavirin restored the lymphoid tissue architecture and reduced the emergence of germinal centers. Electron microscopic examination of renal cortex of animals treated with PFA at 360 mg/kg/day revealed clear mitochondrial necrosis (bursting of mitochondria) of the distal tubules and vacuolization of the proximal tubules which was more striking with combination therapy. Regarding hematotoxicity, PFA did not cause significant hematotoxicity at both doses, whereas ribavirin was hematotoxic at both doses (50 and 100 mg/kg/day), this toxicity being more evident at the higher dose. In conclusion, treatment with ribavirin showed clear efficacy against MAIDS whereas PFA had no efficacy. Furthermore, ribavirin treatment caused hematoxicity and PFA treatment resulted in nephrotoxicity.

New approaches to using antiretroviral therapy for the management of HIV Infection

OBJECTIVE

To review the changes that have occurred in the past 2 years in the management of HIV infection with antiretroviral agents by contrasting the 1994 with the 1996 Guidelines.

DATA SOURCES

Conference proceedings, clinical experience of the author and her colleagues, and English-language articles from the body scientific literature identified via MEDLINE, AIDSLINE, and Current Contents served as data sources.

DATA SYNTHESIS

Current antiretroviral management strategies include movement away from using zidovudine monotherapy, institution of combination antiretroviral therapy earlier in HIV diseases, the use of newer agents such as lamivudine, protease inhibitors (i.e., saquinavir, ritonavir, indinavir), and nonnucleoside reverse transcriptase inhibitors (i.e., nevirapine, delavirdine), prevention of vertical transmission with zidovudine, and use of HIV-1 RNA determinations (viral load) to guide the initiation and alteration of antiretroviral therapy. These strategies represent a dramatic change from the 1994 Guideline, which recommended zidovudine monotherapy in nonpregnant and pregnant individuals whose CD4 cell counts were less than 500 cells/mm3, when many of the newer agents were not available and the assays to determine viral load were strictly investigational.

CONCLUSIONS

The difference between the 1994 and 1996 Guidelines is substantial. It is likely that within a year's time, newer information on pathogenesis and antiretroviral agents in development will be known and further management strategies will need to be disseminated. Until then, the International AIDS Society--USA Guidelines for 1996 should be followed as the standard of care.

Antiretroviral effect of zidovudine-didanosine combination on blood and lymph nodes

OBJECTIVE

To evaluate the antiretroviral effect of a combination of zidovudine (ZDV) and didanosine (ddl) on plasma, peripheral blood mononuclear cells (PBMC) and lymph nodes after 24 weeks.

METHODS

Eight patients naive of antiretroviral therapy were followed by monthly blood samples and two surgical lymph-node biopsies taken at baseline and after 24 weeks. CD4+ T cells were counted monthly by flow cytometry. Plasma HIV-1 RNA was measured monthly by polymerase chain reaction (PCR). Infectious cellular viraemia was measured monthly by a culture technique. Proviral DNA titres in PBMC were measured by endpoint dilution PCR at baseline and 24 weeks. Infectious HIV-1 and proviral DNA titres were measured in the lymph-node mononuclear cells (LNMC). The total HIV-1 RNA content of lymph nodes was measured by PCR. In some cases, phenotypic resistance to ZDV was measured, and codon 215 and 74 mutations in PBMC and LNMC were analysed.

RESULTS

A mean increase in CD4 cell count of 122 x 10(6)/l, a mean decrease in HIV-1 RNA of 1.47 log10 in plasma and a mean decrease in HIV-1 DNA titre of 0.63 log10 were found after 24 weeks of therapy. Nevertheless, there were no statistically significant changes in the mean infectious HIV-1 titre in PBMC and LNMC, in the HIV-1 DNA titre in LNMC or in the total lymph-node HIV-1 RNA burden at week 24. Phenotypic or genotypic markers of drug resistance were rarely found in PBMC at week 24, although they were detected in LNMC from some patients.

CONCLUSION

A discrepancy in the therapeutic effect can be observed between lymphoid organs and blood after 24 weeks of therapy with ZDV and ddl. This difference could be explained by the insufficient antiretroviral potency of this combination facing the significant viral burden present in lymph nodes. Development of drug resistance in this compartment prior to blood can be demonstrated in some cases, although other mechanisms remain to be investigated in future studies to explain this difference.

Effect of combination therapy with zidovudine and didanosine on neuropsychological functioning in patients with symptomatic HIV disease: a comparison of simultaneous and alternating regimens

OBJECTIVE

To evaluate the effects of treatment with alternating and simultaneous regimens of zidovudine and didanosine on neuropsychological function in patients with symptomatic HIV-1 disease, focusing on patients with possible HIV-1-associated central nervous system (CNS) compromise at entry.

DESIGN

Randomized non-blinded clinical trial.

SETTING

Government medical research center.

PATIENTS

Thirty-eight patients with symptomatic HIV-1 disease, of whom 21 had evidence of CNS compromise at entry.

RESULTS

After 12 weeks of therapy, overall significant improvements in memory (P < 0.01) and focused attention (P < 0.001) were seen on both regimens. These gains, however, were largely limited to those patients with HIV-1-associated CNS compromise at entry (P < 0.05). Improvements were also noted in receptive vocabulary, reading, perceptual discrimination and reasoning, divided attention, motor strength, and in mood and affect. Improvements in those latter functions were generally of limited magnitude and were of comparable size for both compromised and non-compromised patients. There was no overall difference between the two drug regimens in the effects on CNS parameters.

CONCLUSIONS

Therapy-related improvements were noted particularly for patients with HIV-1-associated CNS compromise. Neuropsychological functions that have been implicated in AIDS dementia--memory and attention--showed the greatest gains. In contrast to the previously described superiority of the simultaneous regimen with regard to immunologic and virologic parameters, there was no difference between the regimens with regard to CNS measures. This supports the contention that the CNS constitutes a relative independent compartment in terms of HIV disease and treatment.

Alternating treatment with didanosine and zidovudine versus either drug alone for the treatment of advanced HIV infection. The Alter Study. Nordic HIV Therapy Group

The efficacy and safety of an alternating regime with zidovudine and didanosine versus treatment with either drug alone were investigated in a randomized, open, controlled trial, 552 patients with advanced HIV infection, 47% of whom had received prior treatment with zidovudine, were enrolled. The patients were randomly assigned to zidovudine 600 mg/day, didanosine 400 mg/day or 4-week alternations with the 2 drugs in the same dose. The study had a median length of follow-up of 88 weeks. In the overall analyses, time to death (p = 0.48) and time to death or new AIDA event (0.80) were equally distributed between the 3 treatment groups. In the subgroup of patients with a CD4 count < 100 x 10(6)/l the survival was longer in the alternating arm (p < 0.005) primarily because of differences among zidovudine naive patients. The alternating regime was better tolerated than the 2 monotherapies, with a longer time to dose reduction or withdrawal owing to side effects (p < 0.001).

A trial comparing nucleoside monotherapy with combination therapy in HIV-infected adults with CD4 cell counts from 200 to 500 per cubic millimeter. AIDS Clinical Trials Group Study 175 Study Team

BACKGROUND

This double-blind study evaluated treatment with either a single nucleoside or two nucleosides in adults infected with human immunodeficiency virus type 1 (HIV-1) whose CD4 cell counts were from 200 to 500 per cubic millimeter.

METHODS

We randomly assigned 2467 HIV-1--infected patients (43 percent without prior antiretroviral treatment) to one of four daily regimens: 600 mg of zidovudine; 600 mg of zidovudine plus 400 mg of didanosine; 600 mg of zidovudine plus 2.25 mg of zalcitabine; or 400 mg of didanosine. The primary end point was a > or = 50 percent decline in the CD4 cell count, development of the acquired immunodeficiency syndrome (AIDS), or death.

RESULTS

Progression to the primary end point was more frequent with zidovudine alone (32 percent) than with zidovudine plus didanosine (18 percent; relative hazard ratio, 0.50; P<0.001), zidovudine plus zalcitabine (20 percent; relative hazard ratio, 0.54; P<0.001), or didanosine alone (22 percent; relative hazard ratio, 0.61; P<0.001). The relative hazard ratios for progression to an AIDS-defining event or death were 0.64 (P=0.005) for zidovudine plus didanosine, as compared with zidovudine alone, 0.77 (P=0.085) for zidovudine plus zalcitabine, and 0.69 (P=0.019) for didanosine alone. The relative hazard ratios for death were 0.55 (P=0.008), 0.71 (P=0.10), and 0.51 (P=0.003), respectively. For zidovudine plus zalcitabine, the benefits were limited to those without previous treatment.

CONCLUSIONS

Treatment with zidovudine plus didanosine, zidovudine plus zalcitabine, or didanosine alone slows the progression of HIV disease and is superior to treatment with zidovudine alone. Antiretroviral therapy can improve survival in patients with 200 to 500 CD4 cells per cubic millimeter.

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.

Didanosine measurement by radioimmunoassay

Didanosine is commonly prescribed as monotherapy or as part of a combination regimen for patients with human immunodeficiency virus infection. The use of lower doses, either as part of a combination regimen or as a result of dose reduction secondary to clinical intolerance, requires that a sensitive assay method be available for either traditional or population-based pharmacokinetic evaluations. We evaluated a radioimmunoassay technique with a standard curve range of 0 to 100 ng/ml in human plasma, urine, and cerebrospinal fluid and assessed its accuracy and precision for use in pharmacokinetic studies.

Inhibition of murine AIDS by combination of AZT and dideoxycytidine 5'-triphosphate

SUMMARY

A combination of antiretroviral drugs acting on different cell types (lymphocytes and macrophages) was evaluated in a murine retrovirus-induced immunodeficiency model of AIDS (MAIDS). In a first experiment, C57BL/6 mice were infected with a single i.p. administration of LP-BM5 and treated with 0.125 or 0.25 mg/ml AZT in drinking water for 3 months. AZT treatment was found to reduce lymphadenopathy (60 and 65 percent, respectively), splenomegaly (37 and 50 percent, respectively), and hypergammaglobulinemia (6 and 50 percent, respectively). Furthermore, at the highest AZT concentration, BM5d proviral DNA content in lymph nodes and in the spleen showed a reduction of 78 and 70 percent, respectively, compared to untreated animals. In a second experiment, infected mice were treated with AZT (0.25 mg/ml in drinking water) and with 2',3'-dideoxycytidine 5'-triphosphate (ddCTP) encapsulated into autologous erythrocytes for macrophage protection. Combined treatments resulted in a further reduction of lymphadenopathy (a further 33 percent with respect to the single treatment of AZT) and splenomegaly (a further 28 percent respect to the single treatment of AZT) but not of gammaglobulinemia. Proviral DNA in lymph nodes and spleen showed a reduction of 82 and 77 percent, respectively, compared to infected mice. Stimulation index of T cells was also significantly increased in animals receiving both treatments versus AZT only. In conclusion, the selective administration of antiviral drugs that preferentially protect different cell types seems to provide additional advantages compared to single-agent therapy.

Efficacy of combination antiretroviral therapy

Combination therapy with two nucleosides has been shown to improve clinical outcome compared with zidovudine monotherapy. There is every expectation that more potent antiretroviral combination regimens will increase the clinical benefits. However, this remains to be proven definitely. The increasing number of choices of antiretroviral therapies create new challenges for those studying and those using these therapies.

Treatment with lamivudine, zidovudine, or both in HIV-positive patients with 200 to 500 CD4+ cells per cubic millimeter. North American HIV Working Party

BACKGROUND

The reverse-transcriptase inhibitor lamivudine has in vitro synergy with zidovudine against the human immunodeficiency virus (HIV). We studied the activity and safety of lamivudine plus zidovudine as compared with either drug alone as treatment for patients with HIV infection, most of whom had not previously received zidovudine.

METHODS

Three hundred sixty-six patients with 200 to 500 CD4+ cells per cubic millimeter who had received zidovudine for four weeks or less were randomly assigned to treatment with one of four regimens: 300 mg of lamivudine every 12 hours; 200 mg of zidovudine every 8 hours; 150 mg of lamivudine every 12 hours plus zidovudine; or 300 mg of lamivudine every 12 hours plus zidovudine. The study was double-blind and lasted 24 weeks, with an extension phase for another 28 weeks.

RESULTS

Over the 24-week period, the low-dose and high-dose regimens combining lamivudine and zidovudine were associated with greater increases in the CD4+ cell count (P = 0.002 and P = 0.015, respectively) and the percentage of CD4+ cells (P < 0.001 for both) and with greater decreases in plasma levels of HIV-1 RNA (P < 0.001 for both) than was treatment with zidovudine alone. Combination therapy was also more effective than lamivudine alone in lowering plasma HIV-1 RNA levels and increasing the percentage of CD4+ cells (P < 0.001 for all comparisons), and these advantages persisted through 52 weeks. Adverse events were no more frequent with combination therapy than with zidovudine alone.

CONCLUSIONS

In HIV-infected patients with little or no prior antiretroviral therapy, treatment with a combination of lamivudine and zidovudine is well tolerated over a one-year period and produces more improvement in immunologic and virologic measures than does treatment with either agent alone.

In vitro anti-HIV-1 activity of HIV protease inhibitor KNI-272 in resting and activated cells: implications for its combined use with AZT or ddI

KNI-272, a conformationally constrained human immunodeficiency virus (HIV) protease inhibitor containing a P1 allophenylnorstatine (Apns) ((2S,3S)- 3-amino-2-hydroxy-4-phenylbutyric acid), has been shown to be a selective and potent inhibitor of the replication of a wide spectrum of HIV strains in vitro. When KNI-272 was tested in combination with 3'-azido-2',3'-dideoxythymidine (AZT) or 2',3'-dideoxyinosine (ddI) against a primary HIV-1 isolate in phytohemagglutin-activated peripheral blood mononuclear cells (PHA-PBM), its activity was identified to be additive, but not synergistic or antagonistic, as analyzed with the COMBO program package. When tested alone for anti-HIV-1 activity in resting PBM (R-PBM) and PHA-PBM, KNI-272 was found to be comparably potent against the virus in both target cell populations, whereas AZT was more potent in PHA-PBM than in R-PBM and ddI was more potent in R-PBM. These data suggest a potential clinical application of KNI-272 and its analogs.

Determination of human immunodeficiency virus RNA in plasma and cellular viral DNA genotypic zidovudine resistance and viral load during zidovudine-didanosine combination therapy

Eleven human immunodeficiency virus (HIV)-infected subjects on long-term zidovudine (ZDV) therapy had didanosine (ddI) added to their antiretroviral regimen. HIV RNA in plasma was quantitated by branched-DNA signal amplification assay. Peripheral blood mononuclear cell (PBMC) HIV viral DNA was quantitated by PCR. The relative amounts of wild-type (WT) sequence, ddI resistance-associated codon changes (reverse transcriptase [RT] gene codon 65 K-->R [RT K65R], RT 174V, RT I135K/T/V, and RT M184I/V), and ZDV resistance-associated codon change (RT T215Y/F) from HIV RNA in plasma and RT T215Y/F from PBMC viral DNA were determined by differential hybridization of PCR products from 10 of 11 subjects. All subjects had evidence of RT T215Y/F mutation in both RNA in plasma and PBMC DNA at baseline. Subjects with a mixture of WT and RT T215Y/F HIV RNA in plasma at baseline demonstrated a decline in RNA levels in plasma after the addition of ddI. However, after 6 months of ZDV-ddI therapy, WT HIV RNA in plasma was undetectable in all subjects who had demonstrated a mixture at baseline. Subjects with only RT T215Y/F RNA present in plasma at baseline remained so and demonstrated no decline in RNA levels in plasma. In all subjects, no significant changes in PBMC DNA viral load and RT T215Y/F or WT levels were seen. HIV RNA in plasma demonstrated a significantly higher RT T215Y/F mutant/WT ratio than that of PBMC viral DNA, both at baseline and after ZDV-ddI combination therapy in all subjects. No subjects developed mutations associated with ddI resistance at codons 65, 74, 135, and 184 during this study. This study suggests that determination of relative amounts of RT T215Y/F and WT species from HIV RNA in plasma at baseline may be predictive of virologic response during ZDV-ddI combination therapy.