Ritonavir and saquinavir combination therapy for the treatment of HIV infection

[New strategies for antiretroviral treatment in HIV infected patients]

Medical care of HIV-infected patients has been greatly improved during the last four years with the combination of new highly active drugs and routine monitoring of plasma viral load. Three-drugs regimens including a protease inhibitor are the recommended treatments. The objective is the suppression of viral load below detectable levels and the correction of immune deficit. Non-nucleoside reverse transcriptase inhibitors can be used in new therapeutic regimens. To ameliorate efficacy of the antiretroviral treatment and to avoid viral resistance, the tolerance and the ability to adhere are an important challenge.

Antiretroviral Therapy and the Lipodystrophy Syndrome

‘Lipodystrophy syndrome’ in the setting of HIV infection has come to encompass a collection of morphological and metabolic abnormalities linked with the use of antiretroviral therapy and other risk factors. We review the clinical literature on this subject as it has evolved historically, taking pertinent methodological issues into account.

Pilot study of a combination of highly active antiretroviral therapy and cytokines to induce HIV-1 remission

A pilot study of a combination of highly active antiretroviral therapy (HAART) and cytokines in early HIV-1 infection has been undertaken to test the hypothesis that HIV-1 remission can be reached with this strategy by flushing latently infected viral reservoirs. Ten previously antiretroviral naive patients have received a combination of zidovudine, lamivudine, didanosine, saquinavir, and ritonavir for 72 weeks. Between weeks 12 and 48, three courses of interleukin (IL)-2 (7.5 millions of international units [MUI] twice a day for 5 consecutive days) and 2 courses of gamma-interferon (IFN) (100 microg every other day during 2 weeks) were administered subcutaneously. All patients reached plasma HIV-1 RNA levels < 20 copies/ml within 12 +/- 4 weeks. Transient increases in plasma levels (< 120 copies/ml) were observed during administration of IL-2, but less frequently during gamma-IFN administration. HIV-1 RNA decreased in lymph node cells by approximately 4 log, then remained stable after week 24. A mean drop of -0.8 log in peripheral blood mononuclear cell (PBMC) proviral DNA was observed during the trial. Isolation of potentially infectious HIV-1 was successful in each case by coculture of CD4+ T cells taken at week 72. The 2 patients who stopped therapy at the end of the trial showed rebounding plasma HIV-1 RNA levels within a few weeks. No additional mutations were selected in comparison with those present at baseline in 8 patients. In addition, 2 patients developed new mutations in the reverse transcriptase or protease gene and in 1 case, resistance selection was found in lymphoid tissue HIV-1 RNA but not in latently infected cells. In all cases, a rapid increase in both naive and memory CD4+ T cells was observed, with a reduction in activation markers and preservation of the CD8+CD28+ subset. Consequently, an aggressive regimen of HAART and cytokines administered in early stage disease is associated with a positive effect in terms of proviral load reduction and immune reconstitution but is unable to induce HIV-1 remission, allowing low levels of viral replication to persist in lymphoid reservoirs.

Dual protease inhibitor therapy in the management of the HIV-1

Throughout the first 20 years of the HIV-1 epidemic, there have been tremendous advances in the development of antiretroviral therapy (ART). In 1995, the availability of protease inhibitors (PI) as part of triple drug regimens resulted in durable viral suppression with an associated decline in HIV-1-related morbidity and mortality. Despite this early success, limitations of therapy have become apparent. In particular, the need for highly potent antiviral regimens, the importance of outstanding adherence to therapy, drug-related toxicity and the increasing problem of drug-drug and drug-food interactions. Dual PI therapy has been investigated with the hope of overcoming these problems. Select PI combinations may result in synergistic antiviral activity with enhanced viral suppression. Moreover, the ability of select agents to inhibit the cytochrome P450 (CYP450) system results in pharmacologic enhancement that allows for dosing with fewer pills on a less frequent basis, both of which can enhance drug adherence. Furthermore, these pharmacologic interactions can overcome drug-drug and drug-food interactions. Finally, the ability to increase drug levels using certain PI combinations may allow for drug concentrations to exceed those needed to inhibit resistant strains of HIV-1. The rationale for using dual PI therapy, along with the results of clinical trials using various PI combinations in treatment-naïve and experienced patients, is reviewed in this article.

Safety, tolerability, and antiretroviral effects of ritonavir-nelfinavir combination therapy administered for 48 weeks

OBJECTIVE

To evaluate the safety, tolerability, and anti-HIV activity of ritonavir-nelfinavir (RTV-NFV).

DESIGN

Single-site, open-label, nonrandomized, multiple-dose trial of RTV combined with two doses of NFV in protease inhibitor (PI)-naive, HIV-infected patients.

METHODS

Mean baseline HIV RNA was 39,500 copies/ml; mean baseline CD4 count was 323 cells/mm3. All patients received RTV at a dosage of 400 mg twice daily. Cohorts I (N = 10) and II (N = 10) received NFV at a dosage of 500 mg and 750 mg twice daily, respectively, for the initial 12 weeks of the study before allowing intensification with reverse transcriptase inhibitors.

RESULTS

The commonest effects of RTV-NFV therapy were study drug-related moderate-to-severe diarrhea (9 patients in cohorts I and II) and drug-related moderate-to-severe nausea (4 patients in cohorts I and II). HIV RNA was suppressed in a biphasic manner. At 48 weeks in cohort I, mean HIV RNA reduction was 2.82 log10 copies/ml (standard error [SE] =.61; p =.001; N = 4); mean CD4 cell count increase was 236 cells/mm3 (SE = 67.1; p =.006; N = 4). In cohort II, mean HIV RNA reduction at Week 48 was 2.21 log10 copies/ml (SE =.430; p =. 001; N = 8); mean CD4 cell count increase was 120 cells/mm3 (SE = 47. 5; p =.03; n = 8). In cohort I patients, 2 of 4 completing Week 48 had HIV RNA <20 copies/ml; and 3 of 4 had HIV RNA <400 copies/ml. In cohort II, 2 of 8 patients completing Week 48 had HIV RNA <20 copies/ml and 4 of 8 had HIV RNA <400 copies/ml. In addition, 3 patients in cohort I withdrew because of virologic failure not thought to be related to poor compliance. Moreover, 15 patients elected to add new reverse-transcriptase inhibitors (RTIs) after week 12.

CONCLUSIONS

RTV-NFV with concomitant reverse transcriptase inhibitors is a potential dual-PI option for PI-naive patients.

HIV-1 protease inhibitors decrease proliferation and induce differentiation of human myelocytic leukemia cells

Inhibitors of the protease of human immunodeficiency virus type 1 (HIV-1) may inhibit cytoplasmic retinoic acid-binding proteins, cytochrome P450 isoforms, as well as P-glycoproteins. These features of the protease inhibitors might enhance the activity of retinoids. To explore this hypothesis, myeloid leukemia cells were cultured with all-trans retinoic acid (ATRA) either alone or in combination with the HIV-1 protease inhibitors indinavir, ritonavir, and saquinavir. Consistent with the hypothesis, the HIV-1 protease inhibitors enhanced the ability of ATRA to inhibit growth and induce differentiation of HL-60 and NB4 myeloid leukemia cells, as measured by expression of CD11b and CD66b cell surface antigens, as well as reduction of nitroblue tetrazolium. Growth of ATRA-resistant UF-1 cells was also inhibited when cultured with the combination of ATRA and indinavir. Moreover, indinavir enhanced the ability of ATRA to induce expression of the myeloid differentiation-related transcription factor C/EBPε messenger RNA in NB4 cells by 9.5-fold. Taken together, the results show that HIV-1 protease inhibitors enhance the antiproliferative and differentiating effects of ATRA on myeloid leukemia cells. An HIV-1 protease inhibitor might be a useful adjuvant with ATRA for patients with acute promyelocytic leukemia and possibly retinoid-resistant cancers.

HIV-1 protease inhibitors decrease proliferation and induce differentiation of human myelocytic leukemia cells

Inhibitors of the protease of human immunodeficiency virus type 1 (HIV-1) may inhibit cytoplasmic retinoic acid-binding proteins, cytochrome P450 isoforms, as well as P-glycoproteins. These features of the protease inhibitors might enhance the activity of retinoids. To explore this hypothesis, myeloid leukemia cells were cultured with all-trans retinoic acid (ATRA) either alone or in combination with the HIV-1 protease inhibitors indinavir, ritonavir, and saquinavir. Consistent with the hypothesis, the HIV-1 protease inhibitors enhanced the ability of ATRA to inhibit growth and induce differentiation of HL-60 and NB4 myeloid leukemia cells, as measured by expression of CD11b and CD66b cell surface antigens, as well as reduction of nitroblue tetrazolium. Growth of ATRA-resistant UF-1 cells was also inhibited when cultured with the combination of ATRA and indinavir. Moreover, indinavir enhanced the ability of ATRA to induce expression of the myeloid differentiation-related transcription factor C/EBPε messenger RNA in NB4 cells by 9.5-fold. Taken together, the results show that HIV-1 protease inhibitors enhance the antiproliferative and differentiating effects of ATRA on myeloid leukemia cells. An HIV-1 protease inhibitor might be a useful adjuvant with ATRA for patients with acute promyelocytic leukemia and possibly retinoid-resistant cancers.

Antiretroviral therapy of HIV-1 infection: established treatment strategies and new therapeutic options

Recently, studies have shown that non-nucleoside reverse transcriptase inhibitors, such as efavirenz or nevirapine, in combination with two nucleoside analogues have an antiretroviral potency comparable to protease inhibitor containing regimens. Triple combination therapy that includes a non-nucleoside reverse transcriptase inhibitor can therefore be regarded as an effective alternative first-line treatment of HIV-1 infection.

Safety and pharmacokinetics of once-daily regimens of soft-gel capsule saquinavir plus minidose ritonavir in human immunodeficiency virus-negative adults

Human immunodeficiency virus type 1 (HIV-1) protease inhibitors have dramatically improved treatment options for HIV infection, but frequent dosing may impact adherence to highly active antiretroviral treatment regimens (HAART). Previous studies demonstrated that combined therapy with ritonavir and saquinavir allows a decrease in frequency of saquinavir dosing to twice daily. In this study, we evaluated the safety and pharmacokinetics of combining once-daily doses of the soft-gel capsule (SGC) formulation of saquinavir (saquinavir-SGC) and minidose ritonavir. Forty-four healthy HIV-negative volunteers were randomized into groups receiving once-daily doses of saquinavir-SGC (1,200 to 1,800 mg) plus ritonavir (100 to 200 mg) or a control group receiving only saquinavir-SGC (1,200 mg) three times daily. Saquinavir-SGC alone and saquinavir-SGC-ritonavir combinations were generally well tolerated, and there were no safety concerns. Addition of ritonavir (100 mg) to saquinavir-SGC (1,200 to 1,800 mg/day) increased the area under the concentration-time curve (AUC) for saquinavir severalfold, and the intersubject peak concentration in plasma and AUC variability were reduced compared to those achieved with saquinavir-SGC alone (3,600 mg/day), while trough saquinavir levels (24 h post-dose) were substantially higher than the 90% inhibitory concentration calculated from HIV-1 clinical isolates. Neither increasing the saquinavir-SGC dose to higher than 1,600 mg nor increasing ritonavir from 100 to 200 mg appeared to further enhance the AUC. These results suggest that an all once-daily HAART regimen, utilizing saquinavir-SGC plus a more tolerable low dose of ritonavir, may be feasible. Studies of once-daily saquinavir-SGC (1,600 mg) in combination with ritonavir (100 mg) in HIV-infected patients are underway.

The cumulative occurrence of resistance mutations in the HIV-1 protease gene is associated with failure of salvage therapy with ritonavir and saquinavir in protease inhibitor-experienced patients

Salvage therapy with ritonavir (RTV) and saquinavir (SQV) failed to achieve virological and immunological improvement in 24 HIV-infected patients who discontinued triple therapy with RTV or indinavir (IDV) because of failure or intolerance to treatment. Changes in the HIV-1 protease gene sequence were analyzed prospectively in 14 patients. No primary protease mutation was found prior to the use of protease inhibitors. After 7 months of treatment with IDV or RTV, primary resistance mutations at codons pol 46 and/or pol 82 were observed in 11 of 13 patients. After 16 weeks on RTV-SQV, novel primary mutations related to SQV emerged in 7 of 13 patients, together with an increase in the number of secondary resistance mutations. Our observations indicate that the cumulative occurrence of resistance mutations in the protease gene was associated with failure of antiretroviral therapy. The presence of mutations to a first protease inhibitor may represent a risk factor for the failure of a subsequent treatment with a second line protease inhibitor.

In vitro resistance profile of the human immunodeficiency virus type 1 protease inhibitor BMS-232632

BMS-232632 is an azapeptide human immunodeficiency virus (HIV) type 1 (HIV-1) protease inhibitor that displays potent anti-HIV-1 activity (50% effective concentration [EC(50)], 2.6 to 5.3 nM; EC(90), 9 to 15 nM). In vitro passage of HIV-1 RF in the presence of inhibitors showed that BMS-232632 selected for resistant variants more slowly than nelfinavir or ritonavir did. Genotypic and phenotypic analysis of three different HIV strains resistant to BMS-232632 indicated that an N88S substitution in the viral protease appeared first during the selection process in two of the three strains. An I84V change appeared to be an important substitution in the third strain used. Mutations were also observed at the protease cleavage sites following drug selection. The evolution to resistance seemed distinct for each of the three strains used, suggesting multiple pathways to resistance and the importance of the viral genetic background. A cross-resistance study involving five other protease inhibitors indicated that BMS-232632-resistant virus remained sensitive to saquinavir, while it showed various levels (0. 1- to 71-fold decrease in sensitivity)-of cross-resistance to nelfinavir, indinavir, ritonavir, and amprenavir. In reciprocal experiments, the BMS-232632 susceptibility of HIV-1 variants selected in the presence of each of the other HIV-1 protease inhibitors showed that the nelfinavir-, saquinavir-, and amprenavir-resistant strains of HIV-1 remained sensitive to BMS-232632, while indinavir- and ritonavir-resistant viruses displayed six- to ninefold changes in BMS-232632 sensitivity. Taken together, our data suggest that BMS-232632 may be a valuable protease inhibitor for use in combination therapy.

Influence of follicular dendritic cells on HIV dynamics

In patients infected with human immunodeficiency virus type 1 (HIV-1), a large amount of virus is associated with follicular dendritic cells (FDCs) in lymphoid tissue. To assess the influence of FDCs on viral dynamics during antiretroviral therapy we have developed a mathematical model for treatment of HIV-1 infection that includes FDCs. Here, we use this model to analyse measurements of HIV-1 dynamics in the blood and lymphoid tissue of a representative patient, who was treated with a combination of HIV-1 reverse transcriptase and protease inhibitors. We show that loss of virus from FDCs during therapy can make a much larger contribution to plasma virus than production of virus by infected cells. This result challenges the notion that long-lived infected cells are a significant source of HIV-1 during drug therapy. Due to release of FDC-associated virus, we find that it is necessary to revise upward previous estimates of c, the rate at which free virus is cleared, and delta, the rate at which productively infected cells die. Furthermore, we find that potentially infectious virus, present before treatment, is released from FDCs during therapy and that the persistence of this virus can be affected by whether therapy includes reverse transcriptase inhibitors.

BMS-232632, a highly potent human immunodeficiency virus protease inhibitor that can be used in combination with other available antiretroviral agents

BMS-232632 is an azapeptide human immunodeficiency virus type 1 (HIV-1) protease (Prt) inhibitor that exhibits potent anti-HIV activity with a 50% effective concentration (EC(50)) of 2.6 to 5.3 nM and an EC(90) of 9 to 15 nM in cell culture. Proof-of-principle studies indicate that BMS-232632 blocks the cleavage of viral precursor proteins in HIV-infected cells, proving that it functions as an HIV Prt inhibitor. Comparative studies showed that BMS-232632 is generally more potent than the five currently approved HIV-1 Prt inhibitors. Furthermore, BMS-232632 is highly selective for HIV-1 Prt and exhibits cytotoxicity only at concentrations 6,500- to 23, 000-fold higher than that required for anti-HIV activity. To assess the potential of this inhibitor when used in combination with other antiretrovirals, BMS-232632 was evaluated for anti-HIV activity in two-drug combination studies. Combinations of BMS-232632 with either stavudine, didanosine, lamivudine, zidovudine, nelfinavir, indinavir, ritonavir, saquinavir, or amprenavir in HIV-infected peripheral blood mononuclear cells yielded additive to moderately synergistic antiviral effects. Importantly, combinations of drug pairs did not result in antagonistic anti-HIV activity or enhanced cytotoxic effects at the highest concentrations used for antiviral evaluation. Our results suggest that BMS-232632 may be an effective HIV-1 inhibitor that may be utilized in a variety of different drug combinations.

Cerebrospinal fluid HIV-1 RNA during treatment with ritonavir/saquinavir or ritonavir/saquinavir/stavudine

OBJECTIVE

To assess the HIV-1-RNA response and drug concentrations in cerebrospinal fluid (CSF) and serum during treatment with saquinavir (SQV)/ritonavir (RTV) or SQV/RTV plus stavudine (d4T) in HIV-1 -infected patients.

DESIGN

A multicentre, open-label, randomized controlled trial.

METHODS

A total of 208 protease inhibitor (PI) and d4T-naive, HIV-1-infected patients were treated with RTV 400 mg twice daily and SQV 400 mg twice daily with or without d4T 40 mg twice daily. Intensification with reverse transcriptase inhibitors was allowed if serum HIV RNA remained above 400 copies/ml after 12 weeks. In 27 volunteers, CSF and serum HIV RNA were measured at baseline, weeks 12 and 48, using the Roche Amplicor and the ultrasensitive assay. In 22 patients, serum and CSF drug concentrations were determined at week 12.

RESULTS

The median baseline serum and CSF HIV-RNA concentrations were 4.81 and 3.21 log10 copies/ml, respectively. A difference in the proportion of patients with a CSF HIV-RNA level below the limit of quantification (< LLQ) after 12 weeks was found: four out of 14 (RTV/SQV) versus 12 out of 13 (RTV/SQV/d4T) (P = 0.001). The same results were found using the ultrasensitive assay. Patients with a baseline HIV-RNA level < LLQ in CSF remained < LLQ, regardless of the treatment regimen. Treatment with RTV/SQV alone was the only independent predictor of a CSF HIV-RNA level > LLQ at week 12 in logistic regression analysis (P = 0.005). CSF RTV and SQV concentrations were < LLQ in most patients.

CONCLUSION

RTV/SQV alone cannot suppress detectable CSF HIV-1-RNA levels to < LLQ after 12 weeks of treatment in the majority of patients. CSF drug concentrations of RTV and SQV < LLQ may explain the suboptimal antiretroviral effect in the CSF.

3-year suppression of HIV viremia with indinavir, zidovudine, and lamivudine

BACKGROUND

Antiretroviral regimens containing HIV protease inhibitors suppress viremia in HIV-infected patients, but the durability of this effect is not known.

OBJECTIVE

To describe the 3-year follow-up of patients randomly assigned to receive indinavir, zidovudine, and lamivudine in an ongoing clinical trial.

DESIGN

Open-label extension of a randomized, double-blind study.

SETTING

Four clinical research units.

PATIENTS

33 HIV-infected, zidovudine-experienced patients with serum HIV RNA levels of at least 20,000 copies/mL and CD4 counts ranging from 50 to 400 cells/mm3.

INTERVENTION

Indinavir, zidovudine, and lamivudine.

MEASUREMENTS

Safety assessments, HIV RNA levels, CD4 cell counts, and genotypic analyses.

RESULTS

After 3 years of follow-up, 21 of 31 contributing patients (68% [95% CI, 49% to 83%]) had serum viral load levels less than 500 copies/mL. Twenty of 31 (65% [CI, 45% to 80%]) had levels less than 50 copies/mL. The median increase in CD4 count from baseline was 230 cells/mm3 (interquartile range, 150 to 316 cells/mm3). Nephrolithiasis occurred in 12 of 33 patients (36%).

CONCLUSION

A three-drug regimen of indinavir, zidovudine, and lamivudine suppressed viremia in two thirds of patients for at least 3 years.

Once-daily dosing of saquinavir and low-dose ritonavir in HIV-1-infected individuals: a pharmacokinetic pilot study

OBJECTIVE

To investigate the steady-state pharmacokinetics of a once-daily dosing regimen of saquinavir soft gelatin capsules in combination with a low dose of ritonavir in HIV-1-infected individuals.

DESIGN

Open-label, multi-dose, pharmacokinetic pilot study.

PATIENTS

Seven HIV-1-infected individuals who were treated with saquinavir hard gelatin capsules 400 mg twice daily + ritonavir liquid formulation 400 mg twice daily were switched to saquinavir soft gelatin formulation 1600 mg once daily in combination with ritonavir liquid formulation 200 mg once daily (day 0). Patients were instructed to ingest saquinavir and ritonavir simultaneously in the morning and with a meal.

METHODS

Steady-state pharmacokinetics of saquinavir and ritonavir were assessed during a 24 h dosing interval after 2 weeks of continued therapy (day 14). Plasma saquinavir and ritonavir concentrations were measured using a validated high performance liquid chromatography assay. In addition, plasma HIV-1 RNA, and fasting total cholesterol, high-density lipoprotein, low-density lipoprotein, and triglyceride levels were measured on days 0 and 14. A non-compartmental pharmacokinetic method was used to calculate the area under the plasma concentration versus time curve (AUC[0-24h]), the maximum and trough plasma concentrations (Cmax and Cmin), the time to reach Cmax (Tmax), the elimination half-life (t1/2), the apparent clearance (Cl/F), and the apparent volume of distribution (V/F).

RESULTS

Median (range) values of the pharmacokinetic parameters for saquinavir after 2 weeks of treatment were: AUC[0-24h], 19,802h* ng/ml (3720-74,016); Cmax, 2936 ng/ml (573-6848); Cmin, 84 ng/ml (11-854); Tmax, 3.5 h (3.0-4.0), t1/2, 6.8 h (4.6-10.2); Cl/F, 81 l/h (22-430); V/F, 1189 l (215-3086). Ritonavir concentrations were always below the 90% effective concentration of 2100 ng/ml (median Cmax, 1323 ng/ml; range, 692-1528 ng/ml). No significant changes were observed for total serum cholesterol, high-density lipoprotein, and low-density lipoprotein levels between days 0 and 14 (P > or = 0.24). In six out of seven patients the fasting serum triglyceride levels were lower 2 weeks after the treatment switch (median decrease was 32%, P = 0.03). No significant changes in plasma HIV-1 RNA concentrations were observed between days 0 and 14. The regimen was generally well tolerated.

CONCLUSIONS

This pharmacokinetic study indicates that the combination of 1600 mg of saquinavir (soft gelatin capsules) and 200 mg of ritonavir (liquid formulation) in a once-daily dosing regimen generally results in therapeutic plasma concentrations of saquinavir. Due to the large interindividual variation in saquinavir exposure, the monitoring of saquinavir concentrations in plasma is warranted. These pharmacokinetic findings rationalize the further clinical evaluation of once-daily dosing of this combination of protease inhibitors.

Resistance against reverse transcriptase inhibitors

The response to antiretroviral therapy in human immunodeficiency virus (HIV)-infected patients is limited by the emergence of drug resistance. This resistance is a consequence of the high rate of HIV mutation, the high rate of viral replication (especially when potent multidrug therapies are not used or taken reliably), and the selective effect of these drugs, which favors emergence of mutations that can establish clinical drug resistance. The introduction of highly active antiretroviral therapy (HAART), which typically includes at least 2 nucleoside reverse transcriptase inhibitors (RTIs) and a protease inhibitor or a nonnucleoside RTI, for most treatment-naive patients results in a reduction of viral load below the limit of detection determined by currently available HIV RNA assays. It is this marked reduction that results in durable viral suppression, usually only possible by the simultaneous use of 3 or 4 drugs. The RTI components of HAART are crucial for these benefits of combination therapy. Specific amino acid changes are associated with resistance to several RTIs, but new mutation complexes have been observed that can confer broad cross-resistance within this class. Genotypic and phenotypic resistance assays to measure drug resistance are being developed, but refinements in both methodology and our ability to interpret results of these assays are necessary before they are introduced into widespread clinical use.

HIV-1 protease inhibitors

Treatment of human immunodeficiency virus type 1 (HIV-1) infection with regimens that include protease inhibitors (PIs) has contributed to marked improvements in HIV-related disease progression and mortality. Five PIs are approved by the US Food and Drug Administration and have potent activity in vitro. PIs with 2 nucleoside analogue reverse transcriptase inhibitors have demonstrated prolonged suppression of HIV-1 replication in treated patients and improvements in disease progression and mortality. PIs combined with nonnucleoside reverse transcriptase inhibitors or other PIs produce marked antiretroviral effects. Although not all patients have prolonged responses to PIs, and salvage treatment has had mixed results for patients who have not responded to initial PI therapy or whose HIV RNA levels have relapsed during such therapy, newer PIs currently being developed hold promise. Most patients can successfully tolerate PI-including regimens; however, long-term side effects, such as body fat redistribution, insulin resistance, and increased serum lipids, are now being observed in some patients receiving PI-including therapy.

Using pharmacokinetics to optimize antiretroviral drug-drug interactions in the treatment of human immunodeficiency virus infection

Better understanding of the pharmacokinetics of antiretroviral drugs has resulted in the design of combination therapies for the treatment of human immunodeficiency virus (HIV) infection. This has improved the bioavailability and prolonged the plasma half-life of some of the drugs, resulting in enhanced antiviral activity. However, antiviral combination therapy can also result in adverse drug-drug interactions and diminished antiretroviral activity. In this review, we examine drug interactions involving combinations of protease inhibitors, combinations of protease inhibitors with nonnucleoside reverse transcriptase inhibitors, and combinations of nucleoside analogues for the treatment of patients with HIV infection. We discuss examples and mechanisms of pharmacokinetic interactions that improve or decrease antiviral efficacy.

Ongoing trials in HIV protease inhibitors

The development of antiretrovirals has led to a revolution in the care of patients infected with HIV. What was once a uniformly fatal syndrome has become a more treatable, chronic, infectious disease. Central to this revolution have been the protease inhibitors, a class of drugs with potent antiretroviral activity. The first member of this class was approved for use in 1995 and there are now five protease inhibitors approved by the US Food and Drug Administration (FDA): amprenavir, indinavir, nelfinavir, ritonavir and saquinavir. As a result of the magnitude of the HIV pandemic coupled with the clinically proven efficacy of protease inhibitors, there are currently hundreds of ongoing clinical trials with these agents. Trial designs include comparisons between the various licensed protease inhibitors, comparisons of protease inhibitors to other classes of potent antiretroviral drugs, investigations with new protease inhibitors, investigations of protease inhibitor-related toxicities and attempts at simplifying current dosing regimens.

Toward antiviral strategies that resist viral escape

We studied the effect on viral growth of drugs targeting different virus functions using a computer simulation for the intracellular growth of bacteriophage T7. We found that drugs targeting components of negative-feedback loops gain effectiveness against mutant viruses that attenuate the drug-target interaction. The greater inhibition of such mutants than of the wild type suggests a drug design strategy that would hinder the development of drug resistance.

Antiretoviral Therapy and the Lipodystrophy Syndrome, Part 2: Concepts in Aetiopathogenesis

Clinical research has indicated that the use of nucleoside reverse transcriptase inhibitor (NRTI) and HIV protease inhibitor (PI) therapy is associated with a risk of long-term toxicity syndromes, and that the aetiopathogenesis of these adverse effects is independent of the antiretroviral effects of these drugs. In relation to the lipodystrophy syndrome, it appears that the most powerful determinant of subcutaneous fat wasting is an interaction between these two drug classes. In this review, possible mechanisms underlying the contributions of both PI and NRTI drugs are reviewed, with an emphasis on their effects on adipose tissue. On this basis, an ‘adipocentric’, or minimal model of the syndrome is developed, in which divergent effects at the adipocyte of NRTIs (mitochondrial toxicity) and PIs (insulin resistance and impaired adipocyte maturation) interact to produce a phenotype that is consistent with clinical observations.

Amprenavir in Combination with Lamivudine and Zidovudine versus Lamivudine and Zidovudine Alone in HIV-1-Infected Antiretroviral-Naive Adults

Objectives

To compare the antiviral activity and safety of a new protease inhibitor, amprenavir (141W94) in combination with lamivudine and zidovudine, versus lamivudine and zidovudine alone in HIV-1 infected, antiretroviral-naive subjects.

Design

Subjects ( n=232) with a CD4 T cell count of ≥200 cells/mm3, plasma HIV-1 RNA levels of ≥10000 copies/ml, and ≤4 weeks of prior nucleoside antiretroviral therapy, were stratified according to baseline plasma HIV-1 RNA level (10000–30000; 30000–100000; or >100000 copies/ml). Subjects received double-blind treatment with either 1200 mg amprenavir twice daily in combination with lamivudine (150 mg twice daily) and zidovudine (300 mg twice daily) (amprenavir/lamivudine/zidovudine) or matched placebo, lamivudine and zidovudine for 16 weeks. Thereafter, subjects with confirmed plasma HIV-1 RNA levels of ≥400 copies/ml could add open-label amprenavir or switch to other antiretrovirals and continue treatment for up to a minimum of 48 weeks. The primary endpoint of the study was defined as the proportion of subjects with plasma HIV-1 RNA of <400 copies/ml at 48 weeks.

Results

At 48 weeks, a significantly greater proportion of amprenavir/lamivudine/zidovudine subjects had plasma HIV-1 RNA levels <400 copies/ml than lamivudine/ zidovudine subjects in the overall population: 41 versus 3% (intent-to-treat missing equals failure analysis) ( P<0.001); 93 versus 42% (as-treated analysis) ( P<0.001); and within each of the three randomization strata ( P<0.001). Subjects on amprenavir/lamivudine/ zidovudine experienced longer time to event (permanent discontinuation of randomized therapy or viral rebound) than those on lamivudine/ zidovudine (median of 33 versus 13 weeks; P<0.001). A significantly greater incidence of drug-related nausea, vomiting, rash and oral/perioral paresthesia was observed with amprenavir/lamivudine/zidovudine than with lamivudine/zidovudine.

Conclusions

Amprenavir, in combination with lamivudine and zidovudine, has potent and durable antiviral activity in antiretroviral-naive subjects over 48 weeks. Amprenavir was safe and generally well tolerated.

The effect of treatment intensification in HIV-infection: a study comparing treatment with ritonavir/saquinavir and ritonavir/saquinavir/stavudine. Prometheus Study Group

OBJECTIVE

To evaluate the effect of treatment with ritonavir (RTV)/saquinavir (SQV)/6 stavudine (D4T) or RTV/SQV alone, with treatment intensification if needed, in protease inhibitor- and D4T-naïve HIV-1-infected individuals.

DESIGN

Multicentre, open-label, randomized controlled trial. Two-hundred and eight patients were randomized to receive treatment with RTV 400 mg/SQV 400 mg twice daily or RTV 400 mg/SQV 400 mg/D4T 40 mg twice daily. Intensification of study medication with reverse transcriptase inhibitors was permitted if serum HIV-RNA remained > 400 copies/ml after 12 weeks of treatment. Follow-up of this study was 48 weeks.

RESULTS

In a strict intention-to-treat analysis, counting all dropouts as virological failures, 63% [95% confidence interval (CI), 54-73%] of subjects in the RTV/SQV group (n = 104) reached a serum HIV-RNA < 400 copies/ml at week 48, as compared with 69% (95% CI, 60-78%) in the RTV/SQV/D4T group (n = 104; P = 0.379). In the on-treatment analysis these percentages were 88 and 91% respectively. Thirty-one patients intensified their study medication according to the protocol (28 in the RTV/SQV group, three in the RTV/SQV/D4T group). Thirty out of 31 (97%) patients had a serum HIV-RNA < 400 copies/ml at their last follow-up visit. Ten per cent of patients discontinued study medication due to adverse events.

CONCLUSION

The concept of starting with a simple, potent regimen, that could be intensified if necessary, showed good virological results after 48 weeks in this study, comparable to starting with more drugs from the beginning. Longer follow-up is needed to determine the long-term efficacy of this treatment strategy.

Update on highly active antiretroviral therapy: progress and strategies

HIV patients who have detectable viral loads (1,000-5,000 copies/mL) and/or evidence of immunologic dysfunction (CD4+ T-lymphocyte count < 500/mm3) should be treated with a potent combination antiretroviral regimen. Currently, this is to consist of two nucleoside reverse transcriptase inhibitors (NRTIs) with at least one protease inhibitor (PI), or a non-nucleoside reverse transcriptase inhibitor (NNRTI), or another combination with adequate potency. The specific regimen should be designed to achieve an undetectable viral load by an ultrasensitive method (< 50 copies/mL). It should be chosen with a view towards maximizing adherence and minimizing significant drug-drug interactions and side effects. Long-term adherence with the initial highly-active regimen will minimize development of resistant viral mutants and preclude the use of higher complexity regimens. If a regimen is failing in the setting of adequate patient adherence, a new regimen should be chosen using at least two new medications to which viral strains are likely to be sensitive (by genotyping determination). If this is not possible, one may consider treatment interruption or, depending on the clinical status of the patient, continue the current suboptimal regimen until new drugs become available. The predictive value of resistance testing is currently being examined in patients who have failed their first therapy. Further developments include vaccine, cytokine-, and gene therapy-based treatment strategies.

Interactions among combinations of two and three protease inhibitors against drug-susceptible and drug-resistant HIV-1 isolates

Protease inhibitors used in combination with reverse transcriptase inhibitors have demonstrated potent anti-HIV-1 activity in vitro as well as in vivo. We evaluated interactions among five protease inhibitors: indinavir (IDV), ritonavir (RTV), saquinavir (SQV), amprenavir (APV), and nelfinavir (NFV), when used in combinations of two and three drugs in vitro against several HIV-1 isolates, including those susceptible and resistant to various nucleoside and nonnucleoside reverse transcriptase inhibitors. Interactions ranged from synergy to slight antagonism depending on the viral isolates and the experimental conditions employed. Further clinical evaluation of protease inhibitor combinations is warranted.

Anti-HIV effect of saquinavir combined with ritonavir is limited by previous long-term therapy with protease inhibitors

Combination therapy of saquinavir (SQV) and ritonavir (RTV) seems to have a strong antiretroviral effect pharmacokinetically. The purpose of this study was to examine the effectiveness of combined therapy using SQV and RTV in patients previously treated with protease inhibitors (PIs) and to identify the factors compromising the response to such combination therapy. Nineteen HIV-infected Japanese patients participated in this trial between June 1997 and July 1998, and were monitored until November 1998. Patients were treated with SQV (400 mg twice daily) and RTV (300 or 400 mg twice daily). Among the 17 patients who continued such therapy for longer than 3 months, 6 were responders. Among nonresponders, the duration of PI therapy was longer and a higher frequency of preexisting PI resistance viral mutations was detected than in responders. No significant differences were found in previous use of reverse transcriptase inhibitor therapy, CD4+ and CD8+ T cell counts, viral load at baseline, and plasma concentrations of SQV and RTV between responders and nonresponders. Our results suggest that the response to SQV combined with RTV therapy is complicated by previous long-term treatment with PIs, probably owing to multiple PI resistance mutations. Even in patients with a PI-sensitive HIV genotype, however, resistance mutations can develop during therapy and abrogate the effect of high plasma SQV concentrations.

Pharmacologic considerations for therapeutic success with antiretroviral agents

OBJECTIVE

To explore pharmacologic elements that contribute to therapeutic success with agents used for the treatment of HIV infection.

DATA SOURCES

Primary articles were identified through MEDLINE (January 1990-January 1999) and secondary sources. Conference abstracts were selected by review of published proceedings.

STUDY SELECTION AND DATA EXTRACTION

The author evaluated all articles, and relevant information was selected for incorporation into this review.

DATA SYNTHESIS

Heterogeneity in the response to antiretroviral therapy has been attributed to virologic, immunologic, behavioral, and pharmacologic differences among patients. Patients receiving the same dose of an antiretroviral agent will not have the same systemic or intracellular concentration because of interpatient variability in drug absorption, distribution, metabolism, and excretion. Pharmacologic theory and available clinical data support relationships between drug concentration and anti-HIV effect. Thus, variability in drug concentrations contributes to variability in antiviral effect. Desirable pharmacologic characteristics for an antiretroviral drug include high oral bioavailability, a long elimination half-life, low intra- and interpatient pharmacokinetic variability, and a predictable dose-concentration-effect relationship.

CONCLUSIONS

Treatment of the individual who is infected with HIV is a challenging long-term undertaking. Optimal management requires synthesis of a rapidly evolving base of basic and clinical knowledge. The selection of an antiretroviral regimen based on an understanding of the degree to which each individual agent possesses the desired pharmacologic characteristics should help the healthcare provider to translate the therapeutic principles of treatment of HIV infection into clinical reality for all patients.