Six-week randomized controlled trial to compare the tolerabilities, pharmacokinetics, and antiviral activities of GW433908 and amprenavir in human immunodeficiency virus type 1-infected patients

Chemogenetic ON and OFF switches for RNA virus replication

Therapeutic application of RNA viruses as oncolytic agents or gene vectors requires a tight control of virus activity if toxicity is a concern. Here we present a regulator switch for RNA viruses using a conditional protease approach, in which the function of at least one viral protein essential for transcription and replication is linked to autocatalytical, exogenous human immunodeficiency virus (HIV) protease activity. Virus activity can be en- or disabled by various HIV protease inhibitors. Incorporating the HIV protease dimer in the genome of vesicular stomatitis virus (VSV) into the open reading frame of either the P- or L-protein resulted in an ON switch. Here, virus activity depends on co-application of protease inhibitor in a dose-dependent manner. Conversely, an N-terminal VSV polymerase tag with the HIV protease dimer constitutes an OFF switch, as application of protease inhibitor stops virus activity. This technology may also be applicable to other potentially therapeutic RNA viruses.

Fosamprenavir: Drug Development for Adherence

Objective:

To review the pharmacology, pharmacokinetics, virology, safety, efficacy, and clinical use of fosamprenavir.

Data Sources:

A MEDLINE (1966–July 2005) search was conducted using fosamprenavir, Lexiva, amprenavir, and GW433908 as key words. Abstracts from infectious diseases and HIV scientific meetings were identified. Bibliographies of cited articles were reviewed.

Study Selection and Data Extraction:

All publications, meeting abstracts, and unpublished information were reviewed and relevant items included. Information from in vitro, preclinical, and Phase II and III clinical trials was included.

Data Synthesis:

Fosamprenavir is a protease inhibitor (PI) prodrug used for the treatment of HIV-1 infection. The active moiety, amprenavir, is extensively metabolized by CYP3A4. In clinical trials, fosamprenavir was at least as effective as amprenavir, with a reduced pill burden. Fosamprenavir was developed with the intention of reducing the pill burden associated with amprenavir. It has demonstrated comparable safety and efficacy with comparator Pls and is associated with limited cross-resistance to other Pls.

Conclusions:

Fosamprenavir is a promising antiretroviral agent with favorable efficacy and tolerability. At this time, data indicate the utility of fosamprenavir in treatment-naïve and PI-experienced HIV-infected patients.

Salvage Therapy with Ritonavir-Boosted Amprenavir/Fosamprenavir: Virological and Immunological Response in Two Years Follow-up

OBJECTIVE

To evaluate the efficacy of salvage regimens containing ritonavir-boosted amprenavir (APV/r) or fosamprenavir (FPV/r) in heavily pretreated protease inhibitor (PI)-experienced HIV-1 patients.

METHOD

Evaluation of APV/r- or FPV/r-containing antiretroviral regimens in PI-experienced HIV-1 patients with 2 or more antiretroviral failures. Follow-up continued to 96 weeks with prospective collection of data.

RESULTS

54 episodes (48 on APV/r and 6 on FPV/r) were considered in 45 patients who had received a median of 5 prior antiretroviral regimens (range, 2-13) including a median of 3 PIs (range, 2-4). Median time of treatment at analysis was 72 weeks (range, 12-210). At baseline, plasma viral load (pVL) and CD4 cell count was 67,000 copies/mL and 167 cell/mm(3), respectively. At week 96, the median pVL was < 50 copies/mL and CD4 cell count was 519 cells/mm(3). Proportion of patients with pVL below detection was 62% at week 48 and 61% at week 96. Fifteen patients stopped treatment because of virologic failure; one presented a full resistance profile to APV/r, based on the ANRS 2003 resistance algorithm. Median trough APV plasma concentration 4 weeks after treatment initiation was 1406 ng/mL (range, 452-4321); dose adaptation was required in only 7 patients.

CONCLUSION

This study provides long-term follow-up of APV/r and FPV/r in the setting of salvage therapy, showing a high and sustained rate of virologic and immunologic response.

Frequencies of immune hypersensitivity reaction-associated HLA class I alleles in healthy South African Indian and mixed ancestry populations determined by a novel real-time PCR assay

We have determined the frequencies of human leucocyte antigen (HLA)-B*57:01, HLA-B*35:05, HLA-C*04 and HLA-C*08 in healthy individuals of South African Indian (SAI) ethnicity (n = 50) and South African mixed (SAM) ancestry (n = 50) using real-time allele-specific polymerase chain reaction (AS-PCR) assay. HLA-B*57:01 associates with immune hypersensitivity reaction (IHR) in individuals exposed to abacavir (ABC), while nevirapine (NVP) IHR associates with HLA-B*35:05, HLA-C*04 and HLA-C*08. Real-time AS-PCR assays typically use less DNA, are more cost-effective and rapid compared with conventional genotyping methods, such as sequence-based typing (SBT). The assay was developed using samples of known HLA class I genotype and subsequently applied to the SAI and SAM samples. HLA-B*57:01 was detected in SAM and SAI populations at frequencies of 8.0% and 12.0%, respectively, while HLA-B*35:05 was not found in SAI individuals, but was present in 6.0% of SAM individuals. HLA-C*04 was detected in 22.0% and 24.0% of SAM and SAI individuals, respectively, while 10.0% and 8.0% of SAM and SAI individuals, respectively, were HLA-C*08 positive. This study reports the development of a novel real-time AS-PCR assay to identify HLA class I alleles associated with ABC and NVP IHR and has established the frequencies of these alleles present in healthy SAI and SAM populations. Using South African demographic data, our hypothetical analysis suggests that a substantial number of individuals would benefit from the assay.

Relevance of Liver Failure for Anti-Infective Agents: From Pharmacokinetic Alterations to Dosage Adjustments

The liver is a complex organ with great ability to influence drug pharmacokinetics. Due to its wide array of function, its impairment has the potential to affect bioavailability, enterohepatic circulation, drug distribution, metabolism, clearance, and biliary elimination. These alterations differ widely depending on the cause of the liver failure, if it is acute or chronic in nature, the extent of impairment, and comorbid conditions. In addition, effects on liver functions do not occur in a proportional or predictable manner for escalating degrees of liver impairment. The ability of hepatic alterations to influence PK is also dependent on drug characteristics, such as administration route, chemical properties, protein binding, and extraction ratio, among others. This complexity makes it difficult to predict what these effects have on drugs. Unlike certain classes of agents, efficacy of anti-infectives is most often dependent on fulfilling pharmacokinetic/pharmacodynamic targets, such as C_max/MIC, AUC/MIC, T_>MIC, IC₅₀/EC₅₀, or T>EC₉₅. Loss of efficacy, or conversely, increased risk of toxicity may occur in certain circumstances of liver injury. Although important to consider these potential alterations and their effects on specific anti-infectives, many lack data to constitute specific dosing adjustments, making it important to monitor patients for effectiveness and toxicities of therapy.

Population pharmacokinetic modeling and simulation of amprenavir following fosamprenavir/ritonavir administration for dose optimization in HIV infected pediatric patients

Fosamprenavir (FPV) is the phosphate ester prodrug of the HIV-1 protease inhibitor amprenavir (APV). A pediatric population pharmacokinetic model for APV was developed and simulation was used to identify dosing regimens for pediatric patients receiving FPV in combination with ritonavir (RTV) which resulted in concentrations similar to those in adults receiving FPV/RTV 700/100 mg BID. Pharmacokinetic data was obtained from HIV infected subjects aged 2 months to 18 years receiving either FPV or FPV/RTV. A two-compartment model with first order absorption and elimination was an appropriate structural model. Significant covariates in the model included RTV coadministration on clearance, fed status on bioavailability for the oral suspension, body weight on clearance and volume terms, black race on clearance, and age on clearance. The following FPV/RTV twice daily dosing regimens in pediatric patients delivered plasma APV exposure similar to adults: 45/7 mg/kg in patients weighing <11 kg, 30/3 mg/kg in patients weighing 11 to <15 kg, 23/3 mg/kg in patients weighing 15 to <20 kg, and 18/3 mg/kg in patients weighting ≥20 kg. Additionally children weighing ≥39 kg can receive the adult regimen.

Ritonavir-boosted protease inhibitors in HIV therapy

The advent of combination antiretroviral therapy has led to significant improvement in the care of HIV-infected patients. Originally designed as a protease inhibitor (PI), ritonavir is currently exclusively used as a pharmacokinetic enhancer of other protease inhibitors, predominantly due to ritonavir's potent inhibition of the cytochrome P450 3A4 isoenzyme. Ritonavir-boosting of PIs decrease pill burden and frequency of dosing. Boosted PIs are recommended for first-line therapy in treatment and play a key role in the management of treatment-experienced patients. Potential problems associated with PIs include metabolic abnormalities (e.g. dyslipidemia), increased cardiovascular risk, and drug interactions.

Effect of posaconazole on the pharmacokinetics of fosamprenavir and vice versa in healthy volunteers

OBJECTIVES

To manage the interaction between fosamprenavir/ritonavir and posaconazole, we hypothesized that ritonavir can be replaced by posaconazole as an alternative booster of fosamprenavir with no significant influence on posaconazole pharmacokinetics.

METHODS

This was an open-label, randomized, three period, cross-over, single-centre trial in 24 healthy volunteers. All subjects received the following three treatments for 10 days, separated by washout periods of 17 days: posaconazole 400 mg twice daily; fosamprenavir/ritonavir 700/100 mg twice daily; posaconazole 400 mg twice daily with fosamprenavir 700 mg twice daily.

RESULTS

Twenty subjects completed the trial. Geometric mean ratios (GMR; +90% confidence interval) of posaconazole AUC and C(max) when taken with fosamprenavir versus posaconazole alone were 0.77 (0.68-0.87) and 0.79 (0.71-0.89), respectively. The GMRs of amprenavir AUC and C(max) when taken as fosamprenavir and posaconazole versus fosamprenavir/ritonavir were 0.35 (0.32-0.39) and 0.64 (0.55-0.76), respectively. No serious adverse events were reported during the trial.

CONCLUSION

Unboosted fosamprenavir should not be used concomitantly with posaconazole.

New perspectives on lipid and surfactant based drug delivery systems for oral delivery of poorly soluble drugs

Objectives

The aim of this review is to highlight relevant considerations when implementing a rational strategy for the development of lipid and surfactant based drug delivery system and to discuss shortcomings and challenges to the current classification of these delivery systems. We also aim to offer suggestions for an improved classification system that will accommodate lipid based formulations that are not currently accommodated in the lipid formulation classification system.

Key findings

When categorising lipid and surfactant based drug delivery systems, the current Lipid Formulations Classifications System is a useful tool. However, it does not apply to all marketed lipid and surfactant systems or those reported in research papers. A more profound understanding of the functionalities of lipids and surfactants and their role in emulsion formation will enable a rational development strategy and will create the basis for a revised classification system encompassing all employed lipid and surfactant drug delivery systems.

Summary

The ever-increasing number of poorly soluble compounds in drug discovery and development calls for the serious need for effective and affordable drug delivery strategies that will enhance bioavailability and decrease variability. Lipid and surfactant based drug delivery systems offer these advantages; however, the development of these systems requires proper understanding of the physicochemical nature of the compound as well as the lipid excipients and gastrointestinal digestion. One major challenge of lipid excipients and delivery systems is the varying range of compounds they contain. This has contributed to the challenge of proper characterisation and evaluation of these delivery systems, their stability, classification and regulatory issues, which consequently have affected the number of these formulations that eventually reach the market. Suggestions as to proper classification of these delivery systems based on their main lipid component and recommended use are put forward. The prospect of these delivery systems looks promising.

Comparison of once-daily fosamprenavir boosted with either 100 or 200 mg of ritonavir, in combination with abacavir/lamivudine: 96-week results from COL100758

The long-term efficacy of once-daily (qd) fosamprenavir (FPV) 1400 mg boosted by ritonavir 100 mg (FPV/r100) has not been evaluated previously. A 96-week open-label, randomized, multicenter study compared the efficacy/safety of FPV/r100 with FPV 1400 mg boosted by ritonavir 200 mg qd (FPV/r200), plus abacavir/lamivudine 600 mg/300 mg qd, in antiretroviral-naive, HIV-infected patients with viral load (VL)> or =1000 copies/ml. Primary endpoints were proportion of patients achieving VL <400 copies/ml or discontinuing for drug-related reasons. In the intent-to-treat:exposed (ITT-E) population, missing = failure (M = F), and observed approaches were used to assess between-arm differences in VL responses by Cochran-Mantel-Haenszel test and CD4(+) count by Wilcoxon rank-sum test. One hundred and fifteen (115) patients enrolled, with 58 on FPV/r100 (median VL 4.7 log(10) copies/ml; CD4(+) count 259 cells/mm(3)) and 57 on FPV/r200 (median VL 4.9 log(10) copies/ml; CD4(+) count 179 cells/mm(3)). Fewer FPV/r100-treated patients discontinued treatment prematurely (12 vs. 24) and experienced virologic failure (5 vs. 8, none developing major protease inhibitor resistance mutations). At week 96, more FPV/r100-treated patients had VL <400 copies/ml [ITT-E,M = F: 78% (45/58) vs. 53% (30/57), p = 0.006; observed: 98% (45/46) vs. 94% (30/32)] and VL<50 copies/ml [ITT-E,M = F: 66% (38/58) vs. 53% (30/57); observed: 83% (38/46) vs. 94% (30/32)]. The FPV/r100 and FPV/r200 arms were similar at week 96 regarding median change from baseline in CD4(+) count (+265 vs. +260 cells/mm(3)) and total cholesterol (+33 vs. +35 mg/dl), and in total-cholesterol:HDL-cholesterol ratio (4.0 vs. 4.1) and type/frequency of treatment-related grade 2-4 adverse events, although FPV/r100 was associated with a lower elevation in triglycerides (+27 vs. +48 mg/dl). In conclusion, through 96 weeks, FPV/r100 was more effective and prompted less elevation in triglycerides than FPV/r200.

Once-daily fosamprenavir with ritonavir in the treatment of HIV infection in therapy-naïve patients

Treatment options for HIV patients have dramatically improved since the introduction of efficacious antiretroviral combination therapy more than a decade ago. Treatment regimens have been simplified with fewer pills and fewer daily dosages. Fosamprenavir is a protease inhibitor with a rather long half-life which makes it a candidate for once-daily use. Once-daily dosage of ritonavir-boosted fosamprenavir is approved in the US, but not in Europe, for treatment in patients without prior antiretroviral treatment. Here we review the background and rationale for once-daily dosage of ritonavir-boosted fosamprenavir. The rather limited studies that have been published so far indicate that fosamprenavir 1400 mg may be used once daily boosted with ritonavir. The optimal ritonavir dose to be given together with fosamprenavir is still to be defined, though available results indicate that a dose of 100 mg may be adequate provided that no protease inhibitor resistance is present.

Genotypic resistance to lopinavir and fosamprenavir with or without ritonavir of clinical isolates from patients failing protease inhibitors-containing HAART regimens: prevalence and predictors

The aim of this study was to establish the prevalence and predictors of genotypic resistance of HIV-1 to lopinavir and fosamprenavir from patients failing protease inhibitors (PI)-based regimens. We selected 643 HIV-1-infected patients with available treatment history who underwent genotypic resistance assays for virological failure from a clinical site and from the Stanford database. According to the genotypic resistance interpretation of the Stanford algorithm, proportions of viruses showing full susceptibility to fosamprenavir and lopinavir were 32% and 34%, respectively (p =ns). Proportions of viruses fully susceptible to lopinavir/r and fosamprenavir/r according to the Agence Nationale pour la Recherche sur le SIDA (ANRS) algorithm, were 81% and 81%, respectively. According to the Rega algorithm, proportions of viruses showing full susceptibility to fosamprenavir/r and lopinavir were 80% and 70%, respectively (p<0.001). According to the ANRS and Rega interpretations, the time on therapy predicted susceptibility to lopinavir/r, while susceptibility to fosamprenavir/r according to ANRS was predicted by the number of prior PI regimens experienced. According to the Stanford interpretation, prior indinavir exposure predicted resistance to lopinavir/r and fosamprenavir/r while prior nelfinavir use predicted susceptibility to both drugs. After failing PI-based regimens, the majority of viruses retained a predicted susceptibility to fosamprenavir/r and lopinavir/r. In patients failing PIs, the interpretation of genotypic resistance to fosamprenavir may change considerably according to the different algorithms and in respect to the effect of pharmacokinetic boosting with ritonavir.

Steady-state pharmacokinetics of once-daily fosamprenavir/ritonavir and atazanavir/ritonavir alone and in combination with 20 mg omeprazole in healthy volunteers*

OBJECTIVES

Use of proton pump inhibitors in HIV-infected patients is common. The purpose of this study was to determine the steady-state pharmacokinetics of once-daily (qd) fosamprenavir/ritonavir (FPV/r) and atazanavir/ritonavir (ATV/r) alone and in combination with 20 mg qd omeprazole (OMP) in healthy volunteers.

DESIGN AND METHODS

A prospective, open-label, single-site, two-period, crossover pharmacokinetic study was carried out in healthy volunteers. Subjects received either qd FPV/r 1400 mg/200 mg or ATV/r 300 mg/100 mg in the morning for 14 days and then 20 mg OMP in the evening for an additional 7 days. The pharmacokinetics were assessed over 24 h on days 14 and 21. Following a 2-week washout, subjects repeated the process with the other regimen. Trough protease inhibitor (PI) concentrations were taken on day 16 of each period to assess the impact of a single dose of OMP on ATV and amprenavir (APV) concentrations. Plasma ATV and APV pharmacokinetic parameters were assessed by noncompartmental analysis; geometric mean ratios (GMRs; PI+OMP/PI; 90% confidence interval) were calculated between days 14 and 21.

RESULTS

Nineteen healthy, non-HIV-infected volunteers were evaluated. OMP reduced ATV exposure [area under the concentration curve at 0-24 h (AUC0-24 h)] and the minimum drug concentration (Cmin) by 27% each. In contrast, APV exposure and Cmin were decreased by 4 and 2%, respectively. Four subjects (21%) experienced greater than 50% declines in both ATV AUC0-24 h and Cmin after the addition of OMP; this was not observed in any subject following receipt of FPV/r. No alterations in APV or ATV trough concentrations were observed following a single dose of OMP.

CONCLUSIONS

The addition of 20 mg OMP administered in the evening has minimal effect on APV pharmacokinetics. In contrast, ATV pharmacokinetics were altered; a number of ATV-treated subjects experienced pronounced declines in exposures upon the addition of 20 mg OMP administered in the evening, whereas others experienced little to no change.

Fosamprenavir calcium plus ritonavir for HIV infection

Fosamprenavir is a protease inhibitor (PI) approved for the treatment of HIV-1 infection. Fosamprenavir is a prodrug of amprenavir developed to reduce the pill burden yet maintain the unique resistance pattern and efficacy associated with amprenavir. In a head-to-head, noninferiority trial in antiretroviral treatment-naive HIV-infected patients, the antiviral efficacy and tolerability of ritonavir-boosted fosamprenavir was not inferior to ritonavir-boosted lopinavir, when the PIs were combined with two other nucleoside reverse transcriptase inhibitors. There are fewer studies published about fosamprenavir use in antiretroviral treatment-experienced HIV-infected patients. The high genetic barrier to the development of resistance to fosamprenavir and the low level of cross-resistance between ritonavir-boosted fosamprenavir and other PI regimens are notable. As with amprenavir, gastrointestinal disturbance and rash are the most frequent short-term treatment-limiting events with fosamprenavir. Treatment with ritonavir-boosted fosamprenavir can produce a durable response. To date, fosamprenavir is one of the recommended preferred PI components for the treatment of antiretroviral-naive HIV-infected patients.

Interpretation of genotype and pharmacokinetics for resistance to fosamprenavir-ritonavir-based regimens in antiretroviral-experienced patients

In this study, named the Zephir study (Telzir-pharmacokinetics), 121 antiretroviral-experienced human immunodeficiency virus (HIV) patients failing on highly active antiretroviral therapy (HAART) were included in a prospective cohort and received a fosamprenavir-ritonavir (700 mg/100 mg twice a day)-based regimen. The impact of baseline HIV type 1 (HIV-1) mutations, pharmacokinetic (PK) parameters, and genotype inhibitory quotient (GIQ) on the virological response at week 12 (W12) was assessed. HIV reverse transcriptase and protease were sequenced at W0. The response at W12 was defined as<2.3 log10 HIV-1 RNA copies/ml or a virus load decrease of>or=1 log10 copies/ml. W4 amprenavir PK were determined by high-performance liquid chromatography. Patients had a median of nine previous treatments over 8 years. Median W0 values were as follows: 295 CD4+/microl, 4.4 log10 HIV-1 RNA copies/ml, and 6 protease- and 5 nucleotide reverse transcription inhibitor-related mutations. Respective values for minimum concentration of drug in serum (Cmin) and area under the concentration-time curve (AUC) from 0 to 24 h were 1,400 ng/ml and 35 mg.h/ml. At W12, 52% of the patients were successes, with a median decrease of -0.7 log10 HIV-1 RNA copies/ml. The Zephir mutation score included 12 IAS protease mutations associated with poorer virological response: L10I/F/R/V, L33F, M36I, M46I/L, I54L/M/T/V, I62V, L63P, A71I/L/V/T, G73A/C/F/T, V82A/F/S/T, I84V, L90M, and polymorphism mutations I13V, L19I, K55R, and L89M. Comparing<4 versus>or=4 mutations, HIV-1 RNA decreases were -2.3 log10 copies/ml versus -0.1 log10 copies/ml (P<10(-4)) with 93% versus 19% successes (P<10(-4)), respectively. This score predicted W12 failure with 94% sensitivity, versus 31% for the ANRS 2005 algorithm. Cmin (<1,600 ng/ml), AUC (<40 mg.h/ml), and GIQ (<300) values were associated with failure (all P values were <10(-4)). The need to test genotype-based algorithms using different patient databases before their implementation in clinical practice is highlighted. Specific mutations, PK and GIQ, provide relevant information for monitoring fosamprenavir-ritonavir-based HAART.

Rate of viral evolution and risk of losing future drug options in heavily pretreated, HIV-infected patients who continue to receive a stable, partially suppressive treatment regimen

BACKGROUND

Many treatment-experienced, HIV-infected patients who have limited therapeutic options for complete viral suppression continue to receive a partially suppressive treatment regimen pending the availability of at least 2 new antiretroviral drugs. The major risk of this approach is ongoing viral evolution and the loss of future drug options.

METHODS

Antiretroviral-treated subjects with incomplete viral suppression were sampled from a clinic-based cohort. Inclusion criteria were receipt of a stable treatment regimen for > or = 120 days, a plasma HIV RNA load of > 500 copies/mL, and > or = 1 resistance mutation. Phenotypic and genotypic resistance testing was performed every 4 months.

RESULTS

The 106 patients who were eligible for the study had a median of 3 observations during a median of 11.3 months. An estimated 23% and 18% developed at least 1 new nucleoside analogue and 1 new protease inhibitor mutation at 1 year, respectively. An estimated 30% lost the phenotypic equivalent of 1 susceptible drug at 1 year. A lower number of total mutations at baseline was a significant predictor of developing a new nucleoside analogue mutation (P=.01). At 1 year, the probability that an existing mutation would become undetectable using population-based sequencing was 32%. There was a higher rate of change at nonresistance codons than at codons known to be associated with drug resistance.

CONCLUSIONS

Heavily pretreated patients with HIV infection who remain on a partially suppressive regimen have a measurable risk of losing future drug options, particularly those patients who have few baseline mutations. Resistance mutations vary over time, which suggests that the results of any single resistance test may not be representative of all mutations selected by a given treatment regimen.

Coadministration of esomeprazole with fosamprenavir has no impact on steady-state plasma amprenavir pharmacokinetics

OBJECTIVES

To evaluate the drug interaction between fosamprenavir (FPV) and esomeprazole (ESO) after repeated doses in healthy adults.

METHODS

Subjects received ESO 20 mg once daily (qd) for 7 days followed by either ESO 20 mg qd + FPV 1400 mg twice daily (bid) or ESO 20 mg qd + FPV 700 mg bid + ritonavir (RTV) 100 mg bid for 14 days in arms 1 and 2, respectively. After a 21- to 28-day washout, subjects received either FPV 1400 mg bid for 14 days (arm 1) or FPV 700 mg bid + RTV 100 mg bid for 14 days (arm 2). Pharmacokinetic sampling was conducted on the last day of each treatment.

RESULTS

Simultaneous coadministration of ESO 20 mg qd with either FPV 1400 mg bid or FPV 700 mg bid + RTV 100 mg bid had no effect on steady-state amprenavir pharmacokinetics. The only effect on plasma ESO exposure was a 55% increase in area under the plasma concentration-time curve during a dosing interval, tau[AUC0-tau], after coadministration of ESO 20 mg qd with FPV 1400 mg bid.

CONCLUSIONS

FPV 1400 mg bid or FPV 700 mg bid + RTV 100 mg bid may be coadministered simultaneously with ESO without dose adjustment. However, the impact of staggered administration of proton pump inhibitors (PPI) on plasma amprenavir exposure is unknown at present.

Ritonavir increases plasma amprenavir (APV) exposure to a similar extent when coadministered with either fosamprenavir or APV

To compare the effect of ritonavir on plasma amprenavir pharmacokinetics, healthy adults received either fosamprenavir (700 mg twice a day [BID]) or amprenavir (600 mg BID) alone and in combination with ritonavir (100 mg BID). Ritonavir increased plasma amprenavir pharmacokinetic parameters to a similar extent when coadministered with either fosamprenavir or amprenavir.

New antiretroviral drugs in clinical use

The advent of combination antiretroviral therapy for the treatment of human immunodeficiency virus (HIV) infection has dramatically changed the prognosis and quality of life of HIV-infected adults and children. To date, there are 21 antiretroviral agents available with only 11 agents being approved for the use in young children less than 6 years of age. The currently available antiretroviral agents belong to four different classes; nucleoside/nucleotide reverse transcriptase inhibitors (NRTI, NtRTI), non-nucleoside reverse transcriptase inhibitors (NNRTI), protease inhibitors (PI), and a new class of fusion inhibitors (FI). It is recommended that the treatment regimen should be a combination of at least 3 drugs from different drug classes as this has been shown to slow disease progression, improve survival, and result in better virologic and immunologic responses. Treatment with antiretroviral agents is frequently complicated by the issues of adherence, tolerability, long term toxicity and drug resistance. Many efforts have been made to develop new antiretroviral agents with greater potency, higher tolerability profiles and better convenience. Some new agents are also effective against drug-resistant strains of HIV. Since 2001, there were 7 new antiretroviral agents and 2 fixed-dose multidrug formulations being approved for the treatment of HIV infection, most are approved only for use in adults. In this article, we will review new antiretroviral agents including emtricitabine, tenofovir disoproxil fumarate, atazanavir, fosamprenavir, tipranavir and enfuvirtide. Pediatric information on these drugs will be provided when available.

Fosamprenavir

Fosamprenavir is one of the most recently approved HIV-1 protease inhibitors (PIs) and offers reductions in pill number and pill size, and omits the need for food and fluid requirements associated with the earlier-approved HIV-1 PIs. Three fosamprenavir dosage regimens are approved by the US FDA for the treatment of HIV-1 PI-naive patients, including fosamprenavir 1,400 mg twice daily, fosamprenavir 1,400 mg once daily plus ritonavir 200mg once daily, and fosamprenavir 700 mg twice daily plus ritonavir 100mg twice daily. Coadministration of fosamprenavir with ritonavir significantly increases plasma amprenavir exposure. The fosamprenavir 700 mg twice daily plus ritonavir 100mg twice daily regimen maintains the highest plasma amprenavir concentrations throughout the dosing interval; this is the only approved regimen for the treatment of HIV-1 PI-experienced patients and is the only regimen approved in the European Union. Fosamprenavir is the phosphate ester prodrug of the HIV-1 PI amprenavir, and is rapidly and extensively converted to amprenavir after oral administration. Plasma amprenavir concentrations are quantifiable within 15 minutes of dosing and peak at 1.5-2 hours after fosamprenavir dosing. Food does not affect the absorption of amprenavir following administration of the fosamprenavir tablet formulation; therefore, fosamprenavir tablets may be administered without regard to food intake. Amprenavir has a large volume of distribution, is 90% bound to plasma proteins and is a substrate of P-glycoprotein. With <1% of a dose excreted in urine, the renal route is not an important elimination pathway, while the principal route of amprenavir elimination is hepatic metabolism by cytochrome P450 (CYP) 3A4. Amprenavir is also an inhibitor and inducer of CYP3A4. Furthermore, fosamprenavir is commonly administered in combination with low-dose ritonavir, which is also extensively metabolised by CYP3A4, and is a more potent CYP3A4 inhibitor than amprenavir. This potent CYP3A4 inhibition contraindicates the coadministration of certain CYP3A4 substrates and requires others to be co-administered with caution. However, fosamprenavir can be co-administered with many other antiretroviral agents, including drugs of the nucleoside/nucleotide reverse transcriptase inhibitor, non-nucleoside reverse transcriptase inhibitor and HIV entry inhibitor classes. Coadministration with other HIV-1 PIs continues to be studied.The extensive fosamprenavir and amprenavir clinical drug interaction information provides guidance on how to co-administer fosamprenavir and fosamprenavir plus ritonavir with many other commonly co-prescribed medications, such as gastric acid suppressants, HMG-CoA reductase inhibitors, antibacterials and antifungal agents.

Fosamprenavir: advancing HIV protease inhibitor treatment options

Fosamprenavir, the prodrug formulation of amprenavir, is a protease inhibitor recently approved in the US for the treatment of HIV infection. This agent combines the pharmacological profile of amprenavir with a low pill burden and flexible dosing schedule. Three large international trials have been completed. In treatment-naive patients, fosamprenavir, both ritonavir-boosted and -unboosted, met primary end points of non-inferiority against nelfinavir. Among naive patients, no protease inhibitor mutations emerged in those failing the boosted fosamprenavir regimen. Boosted fosamprenavir was compared to lopinavir/ritonavir in treatment-experienced patients. Non-inferiority was not achieved but similar numbers of patients achieved viral suppression when fosamprenavir was dosed twice-daily. Fosamprenavir demonstrates a favourable lipid profile in naive patients, and a low incidence of adverse effects. Fosamprenavir, as with lopinavir/ritonavir, distinguishes itself among other protease inhibitors with its potent activity in those with advanced HIV. Future trials comparing fosamprenavir with current standard regimens will further assist in defining its role in clinical practice.

Effect of antacids and ranitidine on the single-dose pharmacokinetics of fosamprenavir

Single doses of MAALOX TC and ranitidine were administered separately with 1,400 mg of fosamprenavir (FPV). MAALOX TC decreased the area under the concentration-time curve from 0 to 24 h (AUC(0-24)) for plasma amprenavir (APV) by 18% and the maximum concentration of drug in serum (C(max)) by 35%; the plasma APV concentration at 12 h (C(12)) increased by 14%. Ranitidine at 300 mg decreased the AUC(0-24) for plasma APV by 30% and C(max) by 51%; C(12) was unchanged. FPV may be coadministered with antacids without concern and without separation in dosing; however, caution is recommended when FPV is coadministered with histamine(2)- receptor antagonists or proton pump inhibitors.

A 42-Week Open-Label Study to Assess the Pharmacokinetics, Antiretroviral Activity, and Safety of Amprenavir or Amprenavir plus Ritonavir in Combination with Abacavir and Lamivudine for Treatment of HIV-Infected Patients

The pharmacokinetics, antiviral activity, and safety of an amprenavir-ritonavir (APV-RTV) 600/100 mg b.i.d. regimen and an APV-RTV 1200/200 mg q.d. regimen were studied in a human immunodeficiency virus (HIV)-infected population. The geometric least-square mean ratio (90% confidence interval) of steady-state trough concentrations, compared with that of the amprenavir 1200 mg b.i.d. regimen, was 6.08 (4.94-7.49) for the twice-daily APV-RTV regimen, and it was 4.19 (2.90-6.08) for the daily APV-RTV regimen. The regimens were well tolerated, which supports APV-RTV as an option for twice-daily or daily therapy for HIV.

SOLO: 48-week efficacy and safety comparison of once-daily fosamprenavir /ritonavir versus twice-daily nelfinavir in naive HIV-1-infected patients

OBJECTIVE

To compare the magnitude and durability of the antiviral response to fosamprenavir (FPV) plus ritonavir (RTV) once-daily (FPV/r QD) with nelfinavir twice-daily (NFV BID), each administered with abacavir and lamivudine twice-daily.

METHODS

An international, phase III, randomized, open-label study in antiretroviral therapy-naive, HIV-infected adults.

RESULTS

Patients with advanced HIV disease received FPV/r QD (n = 322) or NFV BID (n = 327). At week 48, 69% of patients in the FPV/r QD group and 68% in the NFV BID group had plasma HIV-1 RNA (vRNA) < 400 copies/ml, whereas 55% of patients in the FPV/r QD group and 53% in the NFV BID group had vRNA < 50 copies/ml (intent to treat, rebound/discontinuation = failure). More patients in the NFV BID group (17%) experienced virological failure than in the FPV/r QD group (7%). Efficacy of FPV/r QD was maintained in patients with CD4+ cell counts < 50 x 10 cells/l or vRNA >/= 100 000 copies/ml at entry. At week 48, median CD4+ cell counts were increased to 203 x 10 cells/l (FPV/r QD group) and 207 x 10 cells/l (NFV BID group). Both regimens were generally well tolerated. Diarrhea was more common on NFV BID than on FPV/r QD (16 versus 9%; P = 0.008). Fasting lipid profile results were generally favorable in both treatment arms. FPV/r QD maintained plasma amprenavir (APV) trough concentrations above the mean phenotypic drug-susceptibility (IC50) for wild-type virus for APV.

CONCLUSION

As a first choice protease inhibitor with a low daily pill burden, FPV/r QD was well tolerated and provided potent, durable antiviral suppression.

Fosamprenavir

Fosamprenavir (GW433908, Lexiva, Telzir) is an oral prodrug of the protease inhibitor (PI) amprenavir, with a reduced daily pill burden. Fosamprenavir, in combination with other antiretroviral agents, is indicated for the treatment of patients with HIV infection, particularly those who have not previously received antiretroviral therapy. Viral load reductions were at least as great with fosamprenavir-based regimens as those achieved with nelfinavir-based regimens in two large, 48-week, randomised, multicentre trials in antiretroviral therapy-naive patients with HIV infection. In the NEAT study, more patients receiving twice-daily fosamprenavir in combination with abacavir and lamivudine achieved HIV RNA levels <400 copies/mL than those receiving a similar nelfinavir-based regimen. Results of the SOLO study showed similar reductions in viral load among patients who received once-daily ritonavir-boosted fosamprenavir and those treated with twice-daily nelfinavir, both in combination with twice-daily abacavir and lamivudine. In both trials, virological failure rates were at least twice as high with the nelfinavir-based regimen as they were with the fosamprenavir-based regimen. Fosamprenavir was generally well tolerated in clinical trials. The most common adverse events among patients treated with fosamprenavir, with or without ritonavir, plus abacavir and lamivudine were diarrhoea, nausea, vomiting, abdominal pain, drug hypersensitivity and skin rash. The incidence of diarrhoea was significantly lower with fosamprenavir-based therapy than with nelfinavir-based therapy in the NEAT and SOLO trials. The resistance profile of fosamprenavir is consistent with that of amprenavir. Amprenavir-resistant viral isolates from patients experiencing treatment failure with fosamprenavir-based therapy in the NEAT study showed little or no cross-resistance to several other PIs, and protease mutations commonly selected for by various other PIs were not observed. In the SOLO study, protease resistance mutations were not observed in viral isolates from patients experiencing treatment failure with ritonavir-boosted fosamprenavir-based therapy. In conclusion, fosamprenavir-based regimens have shown good antiviral efficacy and are generally well tolerated in antiretroviral therapy-naive patients with HIV infection. Available data on the resistance profile of the drug suggest that it may be used early in the course of therapy without compromising a range of future treatment options. The relatively low pill burden and lack of food restrictions with fosamprenavir may improve adherence to therapy. Further studies are needed to compare fosamprenavir with other PIs and to establish the long-term efficacy of fosamprenavir-based regimens. In conclusion, fosamprenavir appears to be a promising agent for the treatment of antiretroviral therapy-naive patients with HIV infection.