Simplifying the treatment of HIV infection with ritonavir-boosted protease inhibitors in antiretroviral-experienced patients

Trends in darunavir resistance-associated mutations and phenotypic resistance in commercially tested United States clinical samples between 2006 and 2012

HIV-1 samples submitted by clinicians from the United States for routine drug susceptibility testing (PhenoSense GT) were evaluated for genotypic and phenotypic resistance to darunavir and other protease inhibitors (PIs). Among these samples (Monogram Biosciences database January 2006-June 2012; N=78,843), isolates harboring zero IAS-USA darunavir resistance-associated mutations (RAMs) increased from 77.7% in 2006 to 92.8% through the first half of 2012 (H1 2012; upward trend, p=0.0008); a downward trend seen for samples with three or more darunavir RAMs (7.5% in 2006 and 2.6% in H1 2012; p=0.002). Among samples with any PI resistance (N=15,932), samples harboring zero darunavir RAMs gradually increased (39.9% in 2006 vs. 55.0% in H1 2012; upward trend, p=0.005), but three or more darunavir RAMs did not change over time (21.7% in 2006 and 19.2% in H1 2012; p=0.27). During this period, the frequency of the 11 individual darunavir RAMs (IAS-USA 2011 list) decreased among all samples. The frequency of each darunavir RAM in PI-resistant samples decreased or remained relatively stable. The prevalence of samples with phenotypic resistance to darunavir (partial-to-full) decreased over time in all samples (8.2% in 2006 vs. 2.3% in H1 2012), as did resistance to other PIs (p<0.006 for all PIs). Phenotypic resistance to darunavir and other PIs also decreased in PI-resistant samples (darunavir: 23.9% in 2006 vs. 17.1% in H1 2012; p<0.013 for all PIs). Since approval of darunavir in 2006, there was a significant decrease in prevalence of samples with genotypic and phenotypic resistance to darunavir in commercially tested HIV-1 isolates. Furthermore, the prevalence of phenotypic resistance to darunavir was lower than all other PIs.

Performance of Six Different Ritonavir-Boosted Protease Inhibitor–Based Regimens in Heavily Antiretroviral-Experienced HIV-Infected Patients

BACKGROUND

Regimens based on ritonavir-boosted protease inhibitors (PI/r) are often used as rescue interventions. It is unclear whether significant differences exist between distinct PI/r.

METHOD

All HIV+ patients who had experienced PI failure at two HIV clinics and were rescued with a regimen based on saquinavir (SQV)/r 1000/100 mg bid, indinavir (IDV)/r 800/100 mg bid, lopinavir (LPV)/r 400/100 mg bid, amprenavir (APV)/r 600/100 mg bid, atazanavir (ATV)/r 300/100 mg qd, or tipranavir (TPV)/r 500/200 mg bid were retrospectively examined. A significant virological response (VR) was defined as >1 log reduction in plasma HIV-RNA or to <50 copies/mL at week 24.

RESULTS

A total of 389 patients were included in the analysis: 139 on SQV/r, 35 on IDV/r, 129 on LPV/r, 35 on APV/r, 29 on ATV/r, and 22 on TPV/r. No significant differences in HIV-RNA and CD4 counts at baseline were recognized between groups. In a multivariate analysis, only the total number of protease resistance mutations was associated with a lower VR (odds ratio [OR] = 0.77, 95% CI 0.68-0.87, p < .001). The presence of <5 or > or =5 protease resistance mutations at baseline was the best threshold to discriminate the achievement of VR in any treatment group. In an intent-to-treat analysis, for individuals with 5 protease resistance mutations, the rates of VR were 64% with TPV/r, 47% with LPV/r, 46% with SQV/r, 33% with ATV/r, 25% with IDV/r, and 16% with APV/r. Adverse events leading to treatment withdrawal occurred more frequently using IDV/r (22.8%) than others (p = .03).

CONCLUSION

The rate of VR in salvage therapy using PI/r-based regimens is relatively high in PI-experienced patients. The efficacy is greatly influenced by the number of baseline protease resistance mutations; 5 mutations is the best threshold to predict the chances of VR to any PI/r-based regimen.

Ritonavir-induced hepatotoxicity and ultrastructural changes of hepatocytes

To investigate the effect of ritonavir on hepatocyte proliferation, we detected the change of cleaved caspase-3 expression level in the hepatocytes. Furthermore, the morphological and ultrastructural changes of hepatocytes derived from RTV-treated mice have been observed. The results showed that ritonavir can evidently inhibit hepatocyte proliferation and increase cleaved caspase-3 expression level. Under the electron microscope, chromatin margination, mitochondrial cristae disappearance, karyopyknosis and cytoplasmic vacuolization can be observed in the hepatocytes of mice treated with ritonavir. In conclusion, the mechanism of ritonavir's hepatotoxicity is that it induces apoptosis of hepatocytes via the caspase-cascade system.

Influence of adding etravirine on complexity index and patients' perceived complexity

WHAT IS KNOWN AND OBJECTIVE

Adherence to highly active antiretroviral treatment (HAART) is an important predictive factor of treatment outcome. Medication regimen complexity can be one of the main causes of non-adherence. Thus, treatment simplification is a key strategy in the development of antiretroviral therapy. The aim of this study was to determine the influence of adding etravirine on complexity index and patients' perceived complexity of their treatment regimen.

METHODS

We conducted a prospective two-centre observational study. Patients on etravirine-based therapy, for at least 6 months, who came personally to pharmacy departments for a drug refill from February to July 2012 were included. Data were collected for the current etravirine-based HAART and for the previous HAART without etravirine. The main variables were complexity index and patients' perceived complexity. We also evaluated the adherence during the 6 months before and after the introduction of etravirine into HAART. The complexity index was based on a score which takes into account the number of pills per day, the dosing schedule, the dosage form and any specific instructions linked to use of the drug. To evaluate the patients' perceived complexity of their current and previous HAART, patients were asked to assign a mark on a visual analogue scale ranging from 0 (minimum) to 10 (maximum). We assessed the differences in the variables collected between the current and previous antiretroviral therapy. Finally, we carried out a correlation analysis between the complexity index and the patients' perceived complexity.

RESULTS AND DISCUSSION

Eighty patients were included. The complexity index was significantly reduced after the addition of etravirine to HAART (P = 0·035). Perceived complexity was also reduced (P = 0·015). After the introduction of the drug, the proportion of adherent patients increased from 65% to 81·3% (P = 0·002). The correlation between the complexity index and the patients' perceived complexity was positive (r = 0·594). The correlation increased (r = 0·696) when the difference between the complexity index before and after the introduction of etravirine in HAART grew.

WHAT IS NEW AND CONCLUSION

The addition of etravirine to HAART results in a significant reduction in complexity index and patients' perceived complexity of their therapy. These changes were associated with better adherence to treatment.

Surface-stabilized lopinavir nanoparticles enhance oral bioavailability without coadministration of ritonavir

Aim: The aim of the present study was to prepare surface-stabilized nanoparticles (NPs) for oral bioavailability enhancement of lopinavir (LPN), a Biopharmaceutics Classification System class II antiretroviral drug that possesses low oral bioavailability due to its poor aqueous solubility and extensive metabolism by liver microsomal enzymes. Materials & methods: Surfactant-stabilized LPN-NPs were prepared by combination of antisolvent precipitation and high-pressure homogenization techniques using polyvinyl alcohol as a suitable stabilizer. LPN-NPs were freeze dried by a universal stepwise freeze-drying cycle using mannitol as the cryoprotectant. Pharmacokinetics after oral administration of LPN-NPs were evaluated in male Sprague–Dawley rats and were compared with free LPN coadministered with ritonavir (conventional formulation). Results & conclusion: Freeze-dried stabilized LPN-NPs possessed particle sizes of approximately 320 nm and a narrow particle size distribution (polydispersity index <0.2). The surface-stabilized LPN-NPs (without ritonavir) demonstrated a 3.11-fold enhancement in bioavailability in comparison to free LPN with ritonavir (conventional formulation).

Original submitted 26 March 2012; Revised submitted 14 September 2012; Published online 25 January 2013

A randomised study of the effect of danoprevir/ritonavir or ritonavir on substrates of cytochrome P450 (CYP) 3A and 2C9 in chronic hepatitis C patients using a drug cocktail

PURPOSE

The aim of this study was to evaluate the effects of danoprevir in combination with low-dose ritonavir (danoprevir/r) and placebo plus low-dose ritonavir on the pharmacokinetics of probe drugs for cytochrome P450 (CYP) 3A and CYP2C9, in patients with chronic hepatitis C.

METHODS

A total of 54 patients infected with hepatitis C virus genotype 1 received an oral drug cocktail (2 mg midazolam, 10 mg warfarin and 10 mg vitamin K) before and after 14 days of dosing with either danoprevir/r or placebo plus low-dose ritonavir (placebo/r). Serial pharmacokinetic samples were collected up to 24 (midazolam) and 72 (S-warfarin) h post-dose. Plasma concentrations of midazolam, α-hydroxymidazolam and S-warfarin were measured using validated assays. Pharmacokinetic parameters were estimated using non-compartmental analysis, and geometric mean ratios (GMRs) and 90 % confidence intervals (CIs) for the differences between baseline and post-dosing values were calculated.

RESULTS

Danoprevir/r and placebo/r significantly increased midazolam area under the time-concentration curve (AUC0-∞) and reduced the midazolam metabolic ratio while S-warfarin AUC0-∞ was modestly decreased. When danoprevir data were pooled across doses, the midazolam GMR (90 % CI) AUC0-∞ was 9.41 (8.11, 10.9) and 11.14 (9.42, 13.2) following danoprevir/r and placebo/r dosing, respectively, and the S-warfarin GMR (90 % CI) AUC0-∞ was 0.72 (0.68, 0.76) and 0.76 (0.69, 0.85), respectively. The effects of danoprevir/r and placebo/r appeared to be qualitatively similar.

CONCLUSIONS

Substantial inhibition of CYP3A- and modest induction of CYP2C9- activity were observed with danoprevir/r and low-dose ritonavir.

Metabolism of novel anti-HIV agent 3-cyanomethyl-4-methyl-DCK by human liver microsomes and recombinant CYP enzymes

AIM

To investigate the metabolism of 3-cyanomethyl-4-methyl-DCK (CMDCK), a novel anti-HIV agent, by human liver microsomes (HLMs) and recombinant cytochrome P450 enzymes (CYPs).

METHODS

CMDCK was incubated with HLMs or a panel of recombinant cytochrome P450 enzymes including CYP1A2, 2B6, 2C8, 2C9, 2C19, 2D6, 3A4, and 3A5. LC-ion trap mass spectrometry was used to separate and identify CMDCK metabolites. In the experiments with recombinant cytochrome P450 enzymes, specific chemical inhibitors combined with CYP antibodies were used to identify the CYP isoforms involved in CMDCK metabolism.

RESULTS

CMDCK was rapidly and extensively metabolized by HLMs. Its intrinsic hepatic clearance estimated from the in vitro data was 19.4 mL·min(-1)·kg(-1), which was comparable to the mean human hepatic blood flow rate (20.7 mL·min(-1)·kg(-1)). The major metabolic pathway of CMDCK was oxidation, and a total of 14 metabolites were detected. CYP3A4 and 3A5 were found to be the principal CYP enzymes responsible for CMDCK metabolism.

CONCLUSION

CMDCK was metabolized rapidly and extensively in human hepatic microsomes to form a number of oxidative metabolites. CYP3A4 and 3A5 were the predominant enzymes responsible for the oxidation of CMDCK.

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.

Lopinavir/Ritonavir: a review of its use in the management of HIV-1 infection

Lopinavir/ritonavir (Kaletra®) is an orally administered coformulated ritonavir-boosted protease inhibitor (PI) comprising lopinavir and low-dose ritonavir. It is indicated, in combination with other antiretroviral agents, for the treatment of HIV-1 infection in adults, adolescents and children. Lopinavir/ritonavir is available as a tablet, soft-gel capsule and an oral solution for patients with difficulty swallowing. In well designed, randomized clinical trials, lopinavir/ritonavir, in combination with other antiretroviral therapies (ART), provided durable virological suppression and improved immunological outcomes in both ART-naive and -experienced adult patients with virological failure. Furthermore, lopinavir/ritonavir demonstrated a high barrier to the development of resistance in ART-naive patients. More limited data indicate that it is effective in reducing plasma HIV-1 RNA levels in paediatric patients. Lopinavir/ritonavir has served as a well established benchmark comparator for the noninferiority of other ritonavir-boosted PI regimens. Although generally well tolerated, lopinavir/ritonavir is associated with generally manageable adverse gastrointestinal side effects and hypertriglyceridaemia and hypercholesterolaemia, which may require coadministration of lipid-lowering agents to reduce the risk of coronary heart disease. Lopinavir/ritonavir, in combination with other ART agents, is a well established and cost-effective treatment for both ART-naive and -experienced patients with HIV-1 infection and, with successful management of adverse events, continues to have a role as an effective component of ART regimens for the control of HIV-1 infection.

Synthesis and evaluation of inhibitors of cytochrome P450 3A (CYP3A) for pharmacokinetic enhancement of drugs

The HIV protease inhibitor ritonavir (RTV) is also a potent inhibitor of the metabolizing enzyme cytochrome P450 3A (CYP3A) and is clinically useful in HIV therapy in its ability to enhance human plasma levels of other HIV protease inhibitors (PIs). A novel series of CYP3A inhibitors was designed around the structural elements of RTV believed to be important to CYP3A inhibition, with general design features being the attachment of groups that mimic the P2-P3 segment of RTV to a soluble core. Several analogs were found to strongly enhance plasma levels of lopinavir (LPV), including 8, which compares favorably with RTV in the same model. Interestingly, an inverse correlation between in vitro inhibition of CYP3A and elevation of LPV was observed. The compounds described in this study may be useful for enhancing the pharmacokinetics of drugs that are metabolized by CYP3A.

Efficacy and safety of switching from boosted lopinavir to boosted atazanavir in patients with virological suppression receiving a LPV/r-containing HAART: the ATAZIP study

OBJECTIVES

To evaluate the efficacy and safety of switching from boosted lopinavir (LPV/r) to boosted atazanavir (ATV/r) in virologically suppressed HIV-1-infected patients versus continuing LPV/r.

METHODS

Forty-eight weeks analysis of a randomized, open-label, noninferiority trial including patients with virological suppression (< or = 200 copies/mL for > or = 6 months) on LPV/r-containing triple highly active antiretroviral therapy. Patients (n = 248) were randomized 1:1 either to continue LPV/r twice a day (n = 127) or to switch to ATV/r every day (ATV/r; n = 121), with no change in nucleoside reverse transcriptase inhibitor backbone. Those known to have >4 protease inhibitor (PI)-associated mutations and/or who had failed >2 PI-containing regimens were excluded.

RESULTS

Baseline characteristics were balanced. 30% harboured > or = 1 PI-associated mutation (10% harboured > or = 1 major mutation). Treatment failure at 48 weeks (primary end point) occurred in 20% (25 of 127) of the LPV/r arm and in 17% (21 of 121) of the ATV/r arm (difference -2.3%; 95% confidence interval: -12.0 to 8.0; P = 0.0018). Virological failure occurred in 7% (9 of 127) of the LPV/r arm and in 5% (6 of 121) of the ATV/r arm (difference -2.1%; 95% confidence interval: -8.7% to 4.2%, P < 0.0001 for noninferiorating). CD4 changes from baseline were similar in each arm (approximately 40 cells/mm). Adverse event rate leading to study drug discontinuation was 5% in both arms. Median fasting triglycerides and total cholesterol decreased significantly in the ATV/r arm (-53 and -19 mg/dL, respectively versus -4 and -4 mg/dL in the LPV/r arm; P < 0.001 in both comparisons). Alanine aminotransferase/aspartate aminotransferase hepatic abnormalities were similar in the 2 arms.

CONCLUSIONS

Switching to ATV/r in virologically suppressed patients who were receiving a LPV/r-containing highly active antiretroviral therapy provided comparable (noninferior) efficacy and a safety profile with improved lipid parameters [ISRCTN24813210].

Potential for new antiretrovirals to address unmet needs in the management of HIV-1 infection

Despite the myriad advances in antiretroviral therapy since the original highly active antiretroviral therapy regimens were developed, there remain numerous important and pressing unmet needs that, if addressed, would substantially improve the quality of life and longevity of HIV-infected patients. The most achievable goals of antiretroviral (ARV) therapy in the near future are likely to be continued reduction in HIV-related morbidity and mortality; improved quality of life; and restoration and preservation of immune function: all of which are most effectively achieved through sustained suppression of HIV-1 RNA. The ability to achieve long-term viral load reduction will require new ARVs with few, manageable toxicities, and medications that are convenient to adhere to, with few drug interactions. This is particularly true for the large number of highly treatment-experienced patients in whom HIV has developed resistance to one or more ARVs. Development of therapies that allow convenient dosing schedules, that do not necessitate strict adherence to meal-related timing restrictions, and that remain active in the face of resistance mutations is paramount, and remains a significant unmet need. Of the large number of ARVs currently in development, this article focuses on three agents recently approved that have shown particular promise in addressing some of these unmet needs: the novel non-nucleoside reverse transcriptase inhibitor etravirine; the CCR5 antagonist maraviroc; and the integrase inhibitor raltegravir.

Peptide-modified optical filters for detecting protease activity

The organic derivatization of silicon-based nanoporous photonic crystals is presented as a method to immobilize peptides for the detection of protease enzymes in solution. A narrow-line-width rugate filter, a one-dimensional photonic crystal, is fabricated that exhibits a high-reflectivity optical resonance that is sensitive to small changes in the refractive index at the pore walls. To immobilize peptide in the pore of the photonic crystal, the hydrogen-terminated silicon surface was first modified with the alkene 10-succinimidyl undecenoate via hydrosilylation. The monolayer with the succinimide ester moiety at the distal end served the dual function of protecting the underlying silicon from oxidation as well as providing a surface suitable for subsequent derivatization with amines. The surface was further modified with 1-aminohexa(ethylene glycol) (EG(6)) to resist nonspecific adsorption of proteins common in complex biological samples. The distal hydroxyl of the EG(6) is activated using the solid-phase coupling reagent disuccinimidyl carbonate for selective immobilization of peptides as protease recognition elements. X-ray photoelectron spectroscopy analysis reveals high activation and coupling efficiency at each stage of the functionalization. Exposure of the peptide-modified crystals to the protease subtilisin in solution causes a change in the refractive index, resulting in a shift of the resonance to shorter wavelengths, indicating cleavage of organic material within the pores. The lowest detected concentration of enzyme was 37 nM (7.4 pmol in 200 microL).

Efficacy and safety of atazanavir-based highly active antiretroviral therapy in patients with virologic suppression switched from a stable, boosted or unboosted protease inhibitor treatment regimen: the SWAN Study (AI424-097) 48-week results

BACKGROUND

Atazanavir is a once-daily protease inhibitor (PI) for the treatment of human immunodeficiency virus (HIV) infection that has previously been studied in cohorts of treatment-naive and treatment-experienced patients. Limited data are available on the usefulness of switching from a PI-based regimen to a regimen based on a different PI, such as atazanavir, in HIV-infected patients experiencing virologic suppression but seeking regimen simplification.

METHODS

The Switch to Another Protease Inhibitor (SWAN) study was a 48-week, open-label trial involving HIV-positive patients with virologic suppression who were receiving stable PI-based regimens (with or without ritonavir). Patients were randomized 2 : 1 to switch to atazanavir (400 mg per day)--or, if they were receiving tenofovir, to atazanavir-ritonavir (300/100 mg per day)--or to continue to receive their existing PI. The proportion of patients who experienced virologic rebound (defined as an HIV RNA load >or=50 copies/mL) was compared through study week 48.

RESULTS

Patients either received an atazanavir-containing regimen (278 patients) or continued to receive a comparator PI-containing regimen (141 patients). The proportion of patients who experienced virologic rebound was significantly lower among those who switched to an atazanavir-containing regimen (19 [7%] of 278) than it was among those who continued to receive a comparator PI regimen (22 [16%] of 141; P=.004). Patients who switched to atazanavir therapy experienced significantly fewer total cholesterol, fasting triglyceride, and non-high density lipoprotein cholesterol elevations than did patients in the comparator PI group (P<.001); patients receiving atazanavir had comparable rates of adverse event-related discontinuation and serious adverse events.

CONCLUSIONS

In patients with virologic suppression who were receiving other PIs, switching to a once-per-day regimen containing atazanavir provided better maintenance of virologic suppression (as demonstrated by significantly lower rates of virologic rebound and treatment failure than those observed with continued unmodified therapy), a comparable safety profile, and improved lipid parameters, compared with those for patients who continued their prior PI-based regimen through 48 weeks.

Tipranavir: a new protease inhibitor for the treatment of antiretroviral-experienced HIV-infected patients

Tipranavir (TPV) is a novel non-peptidic protease inhibitor (PI). It binds strongly and selectively to the HIV-1 protease, is orally administered twice daily, boosted with low doses of ritonavir, and shows a favourable resistance profile. In the two registrational trials, named RESIST 1 and 2, TPV/ritonavir 500/200 mg b.i.d., along with an optimised antiretroviral backbone, provided better virologic responses than controls receiving standard of care ritonavir-boosted PI-based regimens. A total of 21 mutations at 16 protease codons have been shown to impact on TPV susceptibility and response rates. The TPV mutation score includes L10V, I13V, K20M/R/V, L33F, E35G, M36I, K43T, M46L, I47V, I54A/M/V, Q58E, H69K, T74P, V82L/T, N83D and I84V. Viruses containing eight or more of these mutations are generally resistant to the drug. TPV use is associated with an excess of grade 3/4 liver enzyme elevations compared with other ritonavir-boosted PIs, and the potential for drug-drug interactions is relevant and must be considered when prescribing TPV.

Lopinavir/ritonavir: a review of its use in the management of HIV infection

Coformulated lopinavir/ritonavir (Kaletra) is a boosted protease inhibitor (PI) containing lopinavir and low-dose ritonavir. It is approved for use in combination with other antiretroviral drugs for the treatment of HIV infection in adults, adolescents and children aged >or=6 months (in the US) or >or=2 years (in the EU).Lopinavir/ritonavir-based antiretroviral therapy (ART) is generally well tolerated and has shown durable virological efficacy in clinical trials in ART-naive and -experienced patients with virological failure. Lopinavir/ritonavir is one of the preferred PIs for first-line treatment of HIV infection in adults, adolescents and children, according to US and British guidelines, reflecting its comparatively better virological efficacy than nelfinavir and low incidence of de novo resistance during long-term treatment. Lopinavir/ritonavir-based treatment may produce a more effective virological response than other PI-based regimens in single PI-experienced, non-nucleoside reverse transcriptase inhibitor (NNRTI)-naive patients. In PI- and NNRTI-experienced patients, atazanavir/saquinavir was inferior to lopinavir/ritonavir; further well designed trials are required to determine the comparative efficacy of lopinavir/ritonavir versus other PIs such as ritonavir-boosted atazanavir, or fosamprenavir or tipranavir in these patients. Lopinavir/ritonavir is more likely than atazanavir (alone or boosted) or nelfinavir to cause hypertriglyceridaemia and is associated with a higher incidence of hypercholesterolaemia than atazanavir (alone or boosted). The new lopinavir/ritonavir tablet coformulation offers a reduced pill count and lack of food interaction, and ART-naive patients in the US and Canada, who are not receiving efavirenz, nelfinavir, nevirapine or amprenavir, may benefit from convenient once-daily administration of lopinavir/ritonavir. Thus, lopinavir/ritonavir is a convenient, effective option for use in the treatment of HIV infection in ART-naive and -experienced adults, adolescents and children.

Effect of rifampin on steady-state pharmacokinetics of atazanavir with ritonavir in healthy volunteers

Mycobacterium tuberculosis is a concern in patients with human immunodeficiency virus (HIV) infection. Rifampin (RIF), an agent used against M. tuberculosis, is contraindicated with most HIV protease inhibitors. Atazanavir (ATV) has clinical efficacy comparable to a standard of care regimen in naive patients and, when dosed with low-dose ritonavir (RTV), also in treatment-experienced patients. We evaluated here the safety and pharmacokinetics of ATV, resulting from three regimens of ATV, RTV, and RIF in 71 healthy subjects. The pharmacokinetics for ATV and RTV were assessed after 6 and 10 days of dosing with ATV 400 mg (n = 53) and with ATV-RTV at 300 and 100 mg (ATV/RTV 300/100; n = 52), respectively. Steady-state pharmacokinetics for ATV, RTV, RIF, and desacetyl-rifampin (des-RIF) were measured after 10 days of dosing of ATV/RTV/RIF 300/100/600 (n = 17), ATV/RTV/RIF 300/200/600 (n = 17), or ATV/RTV/RIF 400/200/600 (n = 14). An RIF 600-alone arm was enrolled as a control group (n = 18). With ATV/RTV/RIF 400/200/600, ATV area under the concentration-time curve values were comparable, but the C(min) values were lower relative to ATV 400 alone. ATV exposures were substantially reduced for the other RIF-containing regimens relative to ATV 400 alone and for all regimens relative to ATV/RTV 300/100 alone. RIF and des-RIF exposures were 1.6- to 2.5-fold higher than with RIF 600 alone. The incidence of grade 3/4 alanine aminotransferase/aspartate aminotransferase values was limited to 1 subject each in both the ATV/RTV/RIF 300/200/600 and the ATV/RTV/RIF 400/200/600 treatments. Coadministration of ATV with RIF was safe and generally well tolerated. Since ATV exposures were reduced in all regimens, ATV and RIF should not be coadministered at the dosing regimens studied.

Plasma amprenavir pharmacokinetics and tolerability following administration of 1,400 milligrams of fosamprenavir once daily in combination with either 100 or 200 milligrams of ritonavir in healthy volunteers

Once-daily (QD) fosamprenavir (FPV) at 1,400 mg boosted with low-dose ritonavir (RTV) at 200 mg is effective when it is used in combination regimens for the initial treatment of human immunodeficiency virus infection. Whether a lower RTV boosting dose (i.e., 100 mg QD) could ensure sufficient amprenavir (APV) concentrations with improved safety/tolerability is unknown. This randomized, two 14-day-period, crossover pharmacokinetic study compared the steady-state plasma APV concentrations, safety, and tolerability of FPV at 1,400 mg QD boosted with either 100 mg or 200 mg of RTV QD in 36 healthy volunteers. Geometric least-square (GLS) mean ratios and the associated 90% confidence intervals (CIs) were estimated for plasma APV maximum plasma concentrations (Cmax), the area under the plasma concentration-time curve over the dosing period (AUC0-tau), and trough concentrations (Ctau) during each dosing period. Equivalence between regimens (90% CIs of GLS mean ratios, 0.80 to 1.25) was observed for the plasma APV AUC0-tau (GLS mean ratio, 0.90 [90% CI, 0.84 to 0.96]) and Cmax (0.97 [90% CI, 0.91 to 1.04]). The APV Ctau was 38% lower with RTV at 100 mg QD than with RTV at 200 mg QD (GLS mean ratio, 0.62 [90% CI, 0.55 to 0.69]) but remained sixfold higher than the protein-corrected 50% inhibitory concentration for wild-type virus, with the lowest APV Ctau observed during the 100-mg QD period being nearly threefold higher. The GLS mean APV Ctau was 2.5 times higher than the historical Ctau for unboosted FPV at 1,400 mg twice daily. Fewer clinical adverse drug events and smaller increases in triglyceride levels were observed with the RTV 100-mg QD regimen. Clinical trials evaluating the efficacy and safety of FPV at 1,400 mg QD boosted by RTV at 100 mg QD are now under way with antiretroviral therapy-naïve patients.