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Pharmacokinetics and safety of GW433908 and ritonavir, with and without efavirenz, in healthy volunteers
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AIDS: Volume 18(6) 9 April 2004 pp 897-907
Wire, Mary Betha; Ballow, Charlesb; Preston, Sandra Lc; Hendrix, Craig Wd; Piliero, Peter Jc; Lou, Yua; Stein, Daniel Sa
From aGlaxoSmithKline, Research Triangle Park, North Carolina; bBuffalo Clinical Research Center, Buffalo, New York; cAlbany Medical College, Albany, New York; and dThe Johns Hopkins Hospital, Baltimore, Maryland, USA.
GW433908 is also known as 908, fosamprenavir or the brand name Lexiva.
"... When EFV is coadministered with the GW433908 700 mg + RTV 100 mg BID regimen, no dosage adjustment is recommended. However, when EFV is coadministered with the GW433908 1400 mg + RTV 200 mg QD regimen, an increase to RTV 300 mg QD is needed to maintain plasma APV exposure...".
The study below provides the results seen from examining the combination of efavirenz (Sustiva) with fosamprenavir ('908', or GW433908). In the article below you can review the study results examining drug blood levels, side effects, clinical adverse events, safety analysis, lab test results, pharmacokinetic (blood levels observed when combining 908 and efavirenz) cholesterol, triglycerides & lipids, etc. As well, following the ABSTRACT and INTRODUCTION below are the author's discussion of the study.
The new form of amprenavir is called fosamprenavir (brand name Lexiva; also called '908'). It is manufactured as a 700 mg pill and can be taken once or twice daily. Twice a day means every 12 hours and once a day means every 24 hours. If taken twice daily the dose is 700 mg plus a 100 mg capsule of ritonavir also taken twice aday along with 908 to boost the blood levels of 908. If taken once daily the dose of 908 is 1400 mg plus a 'booster' of two 100 mg capsules of ritonavir. Of course whichever 908 regimen you take, it's taken along with other HIV antiviral pills in a complete HAART regimen of 3 or 4 different drugs. 908 can be taken with or without food or water. For patients with resistance to several protease inhibitors theonce daily regimen of 908 is not recommended, but it should be used in the twice daily regimen, as it is more effective. The once daily regimen does, however, offer convenience and a low pill burden.
DOSING for THERAPY NAÏVE:
--Lexiva 1400 mg twice daily (without ritonavir)
--Lexiva 1400 mg once daily plusritonavir 200 mg once daily
Lexiva700 mg twice daily plus ritonavir 100 mg twice daily
RECOMMENDED DOSING for Protease Inhibitor-Experienced Patients:
--Lexiva 700 mg twice daily plus ritonavir 100 mg twice daily
--Once daily administration of Lexiva plusritonavir is NOT recommended in protease inhibitor-experienced patients.
DIARRHEA: When Lexiva (1400 mg bid) was compared to nelfinair in a study of 250 patients 5% of patients taking Lexiva and 18% of patients taking nelfinavir 1250mg twice daily reported moderate/severe diarrhea. 34% of patients taking Lexiva and 63% of patients taking nelfinavir reported any diarhhea (all grades of diarrhea). In a study of 650 patients taking Lexiva 1400 mg plus200 mg ritonavir once daily or nelfinavir 1250 mg twice daily , 10% of patients taking Lexiva/r & 18% of patients taking nelfinavir reported moderate/severe diarrhea. 52% of patients taking Lexiva/r and72% of patients taking nelfinavir reported any diarrhea (all grades of diarrhea). In a study comparing 908 700 twice daily plusritinavir 100 mg twice daily to Kaletra, diarrhea reporting was: 13% moderate/severe & 38% all grades for patients taking Lexiva/r, compared to 11% moderate/severe & 47% all grades.
LAB ABNORMALITIES
LIVER ENZYMES: ALT elevations 5 x above the upper limit of normal (ULN) were similar in these studies between the fosamprenavir regimens and the comparator regimens: 4-8%. When comparing 908 bid plus 100 mg RTV bid to Kaletra, 4% taking 908 had ALT 5xULN compared to 4% for Kaletra.
FASTING Hypertriglyceridemia (>750 mg/dL) was reported at 0% for 908 1400 mg bid and 1% for nelfinavir 1250 mg bid. For 908 1400 mg once daily plus ritonavir 200 mg once daily the rate was 6% and 2% for nelfinavir. When comparing 908 700 mg bid plus 100 mg RTV bid to Kaletra, 11% taking 908 and 6% taking Kaletra had hypertriglyceridemia (>750 mg/dL).
Hyperglycemia: rates of grade 3 or 4 hyperglycemia (sugar) was <1% in Lexiva pivotal studies
RASH: 8% of patients taking Lexiva (1400 mg bid) reported moderate/severe rash, and 35% reported all grades of rash. For patients taking nelfinavir 2% reported moderate/severe rash and 19% reported all grades of rash. For patients taking Lexiva/r, 3% reported moderate/severe rash, 17% all grades of rash, compared to patients taking nelfinavir in this study: 2% reported moderate/severe rash & 21% all grades of rash.
The era of once daily HIV regimens is here after several years of anticipation. Reyataz is a protease inhibitor also taken once daily with or without a lowdose ritonavir boost of 100 mg. Of course, efavirenz (Sustiva) is a NNRTI taken once daily. Kaletra is being studied as a once a day protease inhibitor but is currently taken twice daily. In early studies taking Kaletra once daily increased the diarrhea compared to Kaletra taken twice daily. Studies of once daily Kaletra continue. Kaletra offers extra potency. Reyataz studies do not show increases in cholesterol, triglycerides, or glucose. In a 48-week study of Reyataz treatment-naïve patients were followed for body changes and on average the study investigators reported no median changes suggesting that the risk for body changes appear much lower than with other protease inhibitor regimens. Efaviranz also appears to offer a low risk for developing body changes.
There are now a number of nucleosides (NRTIs) that can be taken once daily: 3TC, FTC, ddI, tenofovir (Viread). D4T is approved for once daily but not yet available in the pharmacy. There will soon be a once daily nuke combination pill of 2 nukes. GlaxoSmithKline is developing a once daily regimen abacavir +3TC. And Gilead Sciences is developing a once daily regimen of tenofovir+FTC.
Of course taking HAART once daily offers a more convenient way to take your HIV therapy.
ADDITIONAL RELEVANT INFORMATION ABOUT FOSAMPRENAVIR
DOSING WITH LIVER IMPAIRMENT: The pharmacokinetics of amprenavir have been studied after administration of APV given as Agenerase capsules to adult patients with impaired hepatic function using a single 600-mg oral dose. The AUC of APV was significantly greater in patients with moderate cirrhosis (25.76 mcg.hr/mL) compared with healthy volunteers (12.00 mcg.hr/mL). The AUC and Cmax were significantly greater in patients with severe cirrhosis (AUC 38.66 mcg.hr/mL; Cmax 9.43 mcg/mL) compared to healthy volunteers (AUC 12.00 mcg.hr/mL; Cmax 4.90 mcg/mL). Based on these data the FDA Product Insert says "patients with impaired hepatic function receiving Lexiva without concurrent ritonavir may require dose reduction. There are no data on the use of Lexiva in combination with ritonavir in patients with any degree of hepatic impairment.
METHADONE: Coadministration of amprenavir & methadone as compared to a non-matched control group resulted in a 30%, 27%, and 25$ decrease in amprenavir AUC, Cmax and Cmin, respectively.
STUDY ABSTRACT/SUMMARY
The objective of this study was to evaluate the safety and pharmacokinetic interaction between GW433908, ritonavir (RTV), and efavirenz (EFV).
In period 1, subjects received either a once daily (QD) regimen of GW433908 1395 mg + RTV 200 mg (Study 1) or a twice daily (bid) regimen of GW433908 700 mg + RTV 100 mg (Study 2) for 14 days.
In period 2, subjects received EFV 600 mg QD with either the same GW433908 + RTV regimen as in period 1 (arm 1) or with a GW433908 + RTV regimen that included an additional 100 mg of RTV (arm 2) for 14 days. Amprenavir (APV) pharmacokinetic sampling and safety assessments were performed on the last day of each period.
Plasma APV exposure was not significantly altered when EFV was coadministered with GW433908 700 mg twice daily (BID) + RTV 100 mg BID. Plasma APV exposure was decreased when EFV was coadministered with GW433908 1395 mg QD + RTV 200 mg QD. However, administration of EFV with GW433908 1395 mg QD + RTV 300 mg QD (i.e., adding an extra 100 mg of RTV) was able to negate this interaction. Adverse events were consistent with prior data for each of the separate agents.
When EFV is coadministered with the GW433908 700 mg + RTV 100 mg BID regimen, no dosage adjustment is recommended. However, when EFV is coadministered with the GW433908 1400 mg + RTV 200 mg QD regimen, an increase to RTV 300 mg QD is needed to maintain plasma APV exposure.
Introduction
Lexiva (also called 908 or fosamprenavir) is the new formulation of Agenerase. Agenerase was the brand name for the older form of amprenavir. It was difficult to manufacture and therefore 150 mg pills were needed. So there was a high pill count and the older form was more likely to cause diarrhea because of the ingredients used as fillers in the older form of amprenavir. Vitamin E was used in the older form and is no longer used. 908 can be taken at a dose of 1400 mg twice daily along with other HIV anitivirals in a HAART regimen, or it can be taken either once or twice daily along with a 'boost' from lowdose ritonavir.
GW433908 (also called '908')is the phosphate ester prodrug of the marketed HIV protease inhibitor amprenavir (APV). A prodrug is not an active form of the drug after you ingest it but is processed into an active form by the body. GW433908 is more water soluble and has improved physical properties relative to APV, and therefore can be manufactured into a more compact formulation. 908 is manufactured as 700 mg pills, and if taken twice daily the dose is 1 700 mg 908 pill taken every 12 hours along with the other HIV antiviral pills in your HAART regimen. If taking 908 once daily the dose is 1400 mg of 908 (two 700 mg pills) plus two 100 mg capsules of ritonavir also taken once daily, and of coursethis is taken along with the other HIV antiviral pills in your HAART regimen.
GW433908 appears to be hydrolyzed to APV and inorganic phosphate as it passes through the gut and is absorbed by the intestinal epithelium. Clinical studies of GW433908 in healthy subjects and HIV-infected individuals have shown that following oral administration, GW433908 is rapidly converted to APV with minimal quantifiable GW433908 systemically. GW433908 is a generally well-tolerated and convenient protease inhibitor (flexible dosing, no food or water restrictions) that has demonstrated potency in a phase III clinical development program.
Simplified dosage regimens and low pill burden are two factors that influence medication adherence in HIV/AIDS and other chronic conditions. The compact 700 mg GW433908 tablet formulation allows for a low pill burden (four pills per day). Pharmacological enhancement through drug-drug interactions is another strategy to simplify antiretroviral regimens by permitting less frequent dosing and/or lower doses of individual drugs. The co-administration of GW433908 with ritonavir (RTV), an inhibitor of APV metabolism (via inhibition of the cytochrome P450 isozyme CYP3A4), increases plasma APV concentrations and maintains elevated APV concentrations, thereby allowing the flexibility of once daily (QD) or twice daily (BID) dosing. Large-scale clinical trials have demonstrated the safety and efficacy of three GW433908-containing regimens including two regimens in antiretroviral therapy-naive patients (GW433908 1400 mg BID and GW433908 1400 mg QD + RTV 200 mg QD) and two regimens in protease inhibitor-experienced patients (GW433908 1400 mg QD + RTV 200 mg QD and GW433908 700 mg BID + RTV 100 mg BID).
Efavirenz (EFV) is a non-nucleoside reverse transcriptase inhibitor that has demonstrated safety and efficacy in the treatment of HIV. EFV is also a potent inducer of CYP3A4 and has previously been shown to decrease plasma concentrations of protease inhibitors, including APV, indinavir, lopinavir, and atazanavir. Co-administration of RTV increases plasma concentrations of these protease inhibitors and can counteract the induction effects of EFV in some cases. Thus, we were interested in defining GW433908 + RTV QD and BID dosage regimens that would maintain plasma APV exposure when EFV was coadministered. In addition, the effects of the triple combination on adverse events and clinical laboratory parameters were assessed.
Discussion
Convenient and simple antiretroviral regimens that can provide therapeutic plasma drug concentrations over an entire dosing interval are needed for a growing population of HIV-infected individuals, including those who have exhausted or are close to exhausting all therapeutic options because of drug resistance or an inability to tolerate currently available treatments. The GW433908/RTV QD and BID regimens examined in the two studies reported here were able to maintain plasma APV exposures above the 50% inhibitory concentration (IC50) for APV against HIV from infected individuals who are either antiretroviral-naive or heavily protease inhibitor-experienced. Indeed, these regimens have demonstrated safety, tolerability, and long-term efficacy in both types of HIV-infected populations. GW433908 is a generally well-tolerated and convenient protease inhibitor based on its flexible dosing schedule (QD or BID) and the lack of food or water restrictions.RTV inhibits APV metabolism through CYP3A4, thereby increasing plasma APV concentrations, whereas EFV induces APV metabolism through CYP3A4, thereby decreasing plasma APV concentrations. The pharmacokinetic findings from the two GW433908 + RTV + EFV drug interaction studies reported here demonstrate that the RTV dose required to overcome the CYP3A4 inductive effect of EFV and maintain plasma APV exposure over a dosing interval depends on the dosing schedule. Plasma APV exposures were maintained when EFV 600 mg QD was coadministered with the GW433908 700 mg BID + RTV 100 mg BID regimen, but plasma APV exposure was decreased when EFV 600 mg QD was coadministered with the GW433908 1395 mg QD + RTV 200 mg QD regimen. Increasing the RTV dose to 300 mg QD maintained plasma APV exposure comparable to the GW433908 QD + RTV 200 mg QD regimen without EFV. Plasma RTV Ct,ss values are lower for the RTV 200 mg QD regimen compared to the RTV 100 mg BID regimen, therefore, it is possible that RTV concentrations fall below a level necessary to counteract the EFV induction effect for some portion of the QD dosing interval.
EFV has previously been shown to decrease plasma concentrations of several protease inhibitors, including APV, indinavir, lopinavir, and atazanavir. Co-administration of RTV increases plasma concentrations of APV and some other protease inhibitors and can counteract the induction effects of EFV. Whereas RTV 100 mg BID was sufficient to maintain plasma APV concentrations when coadministered with GW433908 700 mg BID and EFV 600 mg QD, RTV 100 mg BID was not sufficient to counteract the induction effects of EFV on other protease inhibitors administered on a BID schedule, including indinavir and lopinavir.
Drug interaction studies are commonly conducted in a healthy adult population because other variables are minimized and controlled, allowing for an accurate description of the drug interaction. GW433908, RTV, and EFV are intended for use in HIV-infected patients. Similar to the results reported here for two GW433908 + RTV regimens (QD and BID) in healthy adult subjects, plasma APV pharmacokinetics for equimolar APV-containing regimens have been observed in HIV-infected patients. In HIV-infected patients, 300 mg of RTV QD was sufficient to maintain plasma APV concentrations when coadministered with APV 1200 mg QD and EFV 600 mg QD. Furthermore, RTV 100 mg BID appeared sufficient to maintain plasma APV concentrations when coadministered with APV 600 mg BID and EFV 600 mg QD in HIV-infected patients. The similar metabolic drug interactions observed for GW433908 and APV, in addition to the nearly identical plasma APV pharmacokinetic profiles observed for the two compounds, support the applicability of established APV metabolic drug interaction data to GW433908.
A comparison of the plasma APV pharmacokinetic data achieved with the GW433908 + RTV QD and BID regimens suggests that the GW433908 700 mg BID + RTV 100 mg BID regimen delivers similar plasma APV AUCt,ss, slightly lower Cmax,ss, and moderately higher Ct,ss values than the GW433908 1395 mg QD + RTV 200 mg QD regimen. Both GW433908 + RTV regimens maintain plasma APV concentrations above the mean protein-binding adjusted IC50 values for APV against HIV for antiretroviral-naive (0.146 mg/ml) and multiply protease inhibitor-experienced (0.90 mg/ml) HIV-infected individuals. Furthermore, both GW433908 + RTV regimens have demonstrated clinical safety and efficacy in studies of HIV-infected adults.
Plasma RTV exposures achieved with the GW433908 700 mg BID + RTV 100 mg BID regimen are consistent with plasma RTV exposures achieved with other protease inhibitor + RTV combinations, including lopinavir + RTV and saquinavir + RTV and lower than those reported for indinavir + RTV.
Plasma RTV exposure increased (AUCt,ss by 20%, Cmax,ss by 9%, and Ct,ss by 26%) when EFV 600 mg QD was added to the GW433908/RTV BID regimen in period 2 (APV100010: arm 1, treatment E). This increase is consistent with the 20% increase in plasma RTV AUCt,ss reported for the combination of RTV 500 mg BID + EFV 600 mg QD and is unlikely to be of clinical concern as it is still well below that of the approved dose (600 mg BID) or that of a dose shown to have minimal antiviral activity (400 mg BID). Plasma RTV exposure decreased (RTV AUCt,ss by 31%) when EFV 600 mg QD was added to the GW433908/RTV QD regimen in period 2 (APV10009: arm 1, treatment B).
EFV concentrations were not measured in this study because prior data indicated that neither RTV (500 mg BID) nor APV (1200 mg BID) significantly affect EFV concentrations.
All of the side effects associated with the GW433908 regimens reported in these studies in healthy subjects have been previously noted in studies of HIV-infected individuals treated with APV, RTV, and/or EFV, and therefore were not unexpected. Adverse events were reported with similar frequency in the two studies and across the treatment regimens within each study, with the exception of rash and diarrhea/loose stools, which tended to be more common with the GW433908 + RTV treatment (period 1), and dizziness, which tended to be more common with the GW433908 + RTV + EFV treatment (period 2). The adverse events reported in period 2 (GW433908 + RTV + EFV) were probably influenced by the preceding 14 days of GW433908 + RTV dosing in period 1 because there was time for subjects experiencing adverse events to either discontinue or become tolerant to the study medications prior to period 2.
Overall, median laboratory values were stable for clinical chemistry and hematology parameters with the exception of statistically significant increases in fasting serum total cholesterol and triglyceride concentrations. In both studies, increases from baseline in mean fasting serum total cholesterol were noted in all three treatments on day 14 or day 28. In addition, increases from baseline in mean fasting triglyceride concentrations for all three treatments in APV10010 and two treatments in APV10009 (not treatment C) were observed. These elevations persisted and were evident at the 2-week follow-up evaluation.
Using the NCEP criteria, approximately half of the subjects with normal fasting serum total cholesterol concentrations at baseline had high concentrations (>= 240 mg/dl) while on treatment. When evaluating fasting serum triglycerides, no subjects in APV10009 and four of 26 subjects in APV10010 had very high fasting serum triglyceride concentrations (>= 500 mg/dl) while on treatment. Because significant increases in serum cholesterol and triglyceride concentrations have been seen with the protease inhibitors, especially RTV, the observed elevations in these two studies were expected.
In summary, GW433908 is a generally well tolerated HIV protease inhibitor, with a flexible dosing schedule and without food or water restrictions, that has demonstrated potency in treatment-naive and treatment-experienced adult patients. The results of the two studies presented in this manuscript provide useful data on how to dose GW433908 + RTV with EFV. The RTV dose in the BID regimen needed to counteract the CYP3A4 inductive effect of EFV is 100 mg (coadministered with 700 mg GW433908), and the RTV dose in the QD regimen is 300 mg (coadministered with 1400 mg GW433908).
Methods
Study participants
Healthy adult male and female subjects were eligible to participate if they were free of clinically significant illness or disease, were aged >= 18 and <= 60 years, were seronegative for HIV, hepatitis B and C virus, and had a body mass index of 20-32 kg/m2. Men were required to abstain from sexual intercourse or use an acceptable method of birth control during the study and for 2 weeks following study drug discontinuation. Women had to be of non-childbearing potential; breastfeeding women were also excluded. All subjects were informed of all aspects of the study and had to provide written informed consent approved by their local Institutional Review Board prior to study participation. Ineligibility for participation included a clinical history of alcohol or illicit drug use, history of allergy to study medications, presence of any clinically significant abnormality, blood donation of >= 450 ml within 3 months prior to study entry, and use of concurrent medications that could not be withheld for 2 weeks prior to taking the first dose of study drug (day 1) and through study completion.
Study design
Two phase I, open-label, randomized, two-arm, two-period, 28-day studies were conducted at three study centers in the USA (GlaxoSmithKline [GSK] protocols APV10009 and APV10010). All subjects were screened within 28 days of the first day of dosing to determine eligibility for enrollment into the study. Eligible subjects were randomly assigned to one of two arms (arm 1 or arm 2) within each study. APV10009 was conducted between January and March 2001; APV10010, between June and September 2001. The study protocol and informed consent were reviewed and approved by each study center's Institutional Review Board.
Study drugs and dosing
GSK protocol APV10009
All subjects received GW433908 1395 mg QD + RTV 200 mg QD (treatment A) from day 1 through day 14 (period 1); on days 15 through 28 (period 2), subjects in arm 1 received GW433908 1395 mg QD + RTV 200 mg QD + EFV 600 mg QD (treatment B), while subjects in arm 2 received GW433908 1395 mg QD + RTV 300 mg QD + EFV 600 mg QD (treatment C).
GSK protocol APV10010
All subjects received GW433908 700 mg BID + RTV 100 mg BID (treatment D) from day 1 through the morning of day 14 (period 1). From the evening of day 14 through day 28 (period 2), subjects in arm 1 received GW433908 700 mg BID + RTV 100 mg BID + EFV 600 mg QD (treatment E), while subjects in arm 2 received GW433908 700 mg BID + 200 mg BID + EFV 600 mg QD (treatment F).
EFV was administered in the evening, 2 h apart from a meal. GW433908 and RTV were administered in the morning (APV10009) or in the morning and evening (APV10010) without regard to food intake. However, on serial plasma pharmacokinetic sampling days (days 14 and 28), the last of each period's GW433908 plus RTV doses were administered with 180 ml of water following a 10-h fast. Also on these days, subjects fasted for an additional 4 h after administration of the study drugs and additional water was permitted 2 h after study drug administration.
The first and last doses of each period's study drugs were administered at the study center; subjects took the other study drug doses on an out-patient basis. Subjects completed study drug diary cards and returned these and the study drug containers to the study center each week for assessment of adherence.
For APV10009, GW433908 was supplied as oral 465-mg tablets and for APV10010, GW433908 was supplied as 700-mg tablets. Equivalent doses of the two GW433908 tablet strengths (i.e., three 465-mg tablets versus two 700-mg tablets) were determined to be bioequivalent (GSK data on file). In both studies, RTV was supplied as oral 100-mg soft gelatin capsules and EFV was supplied as oral 200-mg capsules. GW433908 and EFV were stored at room temperature; RTV was refrigerated (2-8°C) and protected from light.
Safety assessments
Subjects were asked about clinical adverse events and concurrent medications during screening procedures and while at the study center on days 1, 7, 13-15, 21, 27-29, and at follow-up. Day 1, 14, and 28 clinical laboratory samples were collected following a fast of at least 8 h. Screening and follow-up clinical laboratory samples were collected without food restrictions. Pregnancy testing was performed at screening, prior to dosing on day 1, the evening prior to dosing on days 13 and 27, and at follow-up.
Pharmacokinetic sampling
For APV10009, 15 serial whole blood samples were collected over 24 h (t = 0, 0.5, 0.75, 1, 1.5, 2, 2.5, 3, 4, 5, 8, 10, 12, 16, and 24 h) on days 14-15 (period 1) and days 28-29 (period 2) for the determination of plasma APV, GW433908, and RTV concentrations. For APV10010, 13 serial whole blood samples were collected over 12 h (t = 0, 0.5, 0.75, 1, 1.5, 2, 2.5, 3, 4, 5, 8, 10, and 12 h) on day 14 (period 1) and day 28 (period 2). Additional pharmacokinetic samples were collected on the evenings of day 13 and day 27 for APV trough concentrations (APV10010 only).
A 4.5-ml whole blood sample was collected at each pharmacokinetic sampling time-point in a sodium citrate-containing Vacutainer tube and gently inverted to mix the blood with the anticoagulant. Whole blood samples were kept under refrigerated conditions for up to 1 h before centrifugation. Plasma was separated by refrigerated (4°C) centrifugation at 2000 g for 10 min, divided into two polypropylene tubes, and stored frozen at below -20°C until they were analyzed for APV, GW433908, and RTV concentrations.
Bioanalysis of APV, GW433908, and RTV concentrations in plasma
Plasma samples were analyzed for APV and GW433908 concentrations using a validated high performance liquid chromatography with tandem mass spectrometric detection (HPLC-MS-MS) method following solid phase extraction at GSK (Research Triangle Park, North Carolina, USA). Plasma samples were analyzed for RTV concentration using a validated HPLC method with ultraviolet absorbance detection at PPD Development (Richmond, Virginia, USA). The calibration ranges for the three analytes were: APV, 10-10 000 ng/ml; GW433908, 5-100 ng/ml; RTV, 0.02-15.0 mg/ml. For APV10009, assay accuracies, expressed as percent bias, for each analyte were: APV, <= ± 10.1; GW433908, <= ± 6.5; RTV, <= ± 6.55. Inter-assay precision, measured as percent coefficient of variation (%CV) for each analyte was: APV,: <= 6.9; GW433908, <= 8.3; and RTV, <= 7.61. For APV10010, the assay accuracies, expressed as % bias, for each analyte were: APV, <= ± 6.35; GW433908, <= ± 3.16; RTV, <= ± 6.68. Inter-assay precision, measured as %CV, for each analyte was: APV, <= 7.03; GW433908, <= 7.03; RTV, <= 8.19.
Pharmacokinetic analysis
Pharmacokinetic analyses of plasma APV and RTV concentration-time data were conducted using non-compartmental methods with WinNonlin Professional software, version 3.0 (Pharsight Corporation, Mountain View, California, USA). The maximum concentration at steady-state (Cmax,ss) and the time to reach maximum concentration (Tmax,ss) were obtained from the observed values. The area under the concentration-time curve during a dosing interval, t, at steady-state (AUCt,ss) was calculated using the log-linear trapezoidal method. The concentration at the end of a dosing interval, t, at steady-state (Ct,ss) was calculated as the mean of the pre-dose and either 12 h (APV10010) or 24 h (APV10009) plasma drug concentrations.
Sample size and statistical analysis
A sample size of 12 evaluable subjects per arm (24 total subjects/study) was estimated to provide a 90% confidence interval (CI) within ± 30% of the geometric least squares mean ratio. To obtain 24 evaluable subjects/study, planned enrollment was set at 32 subjects/study (16 per arm) to allow for potential subject withdrawal.
The achievement of steady-state was assessed at the end of each period by ANOVA, considering trough concentration (pre-dose versus 24-h concentrations on the last day of each period) as a fixed effect and subject was considered a random effect in APV10009. In APV10010, the assessment of steady-state was by examination of the slope (90% CI) from linear regression of log-transformed plasma APV trough concentrations following the last three doses with subject fitted as a random effect and time treated as a continuous variable.
All plasma APV and RTV pharmacokinetic parameters, except Tmax,ss, were loge-transformed prior to statistical analysis. For both studies, ANOVA was performed to assess within-subject treatment comparisons of steady-state plasma APV and RTV pharmacokinetic parameters in which treatment was considered a fixed effect and subject was considered a random effect using SAS Mixed Linear Models procedure. The ratio of geometric least squares means and associated 90% CI for the treatment comparisons (ratios of treatment B/A, C/A, E/D, and F/D) were estimated for each plasma APV and RTV pharmacokinetic parameter.
For clinical chemistry data, within-subject day 14, day 28, and follow-up fasting serum cholesterol, triglycerides, and glucose concentrations were compared with day 1 concentrations by ANOVA using the SAS Mixed Linear Models procedure. Day was considered a fixed effect and subject to a random effect. The least squares mean change from baseline and associated standard error were estimated for each treatment and statistical significance was noted at P < 0.05.
Results
Study participants
Baseline characteristics of the 32 subjects enrolled in APV10009 and the 31 subjects enrolled in APV10010 were summarized. In both studies, all enrolled subjects were included in the respective safety analyses. In APV10009, the pharmacokinetic treatment comparisons included 22 of the 32 enrolled subjects (11 per arm) because of premature withdrawals (eight, four from each arm) and/or non-adherence (two, one from each arm). In APV10010, the pharmacokinetic analyses included 24 of the 31 enrolled subjects (14 subjects in arm 1 and 10 subjects in arm 2) because of premature withdrawals (five, one in arm 1 and four in arm 2), dosing errors (one in arm 2), and non-adherence (one in arm 2).
Pharmacokinetics
GW433908
Measurement of plasma GW433908 and APV concentrations in both studies demonstrated that GW433908 is rapidly and extensively converted to APV with minimal GW433908 measured systemically. GW433908 could not be quantified in all subjects (quantified in 19/22 subjects in APV10009 and 12/24 subjects in APV10010). When GW433908 was quantified, concentrations were generally very low (near the limit of detection, 0.005 mg/ml) and quantifiable at 1-9 time points early in the profile (between 0.5 and 5 h post-dosing).
APV; RTV
Steady-state plasma APV concentrations were achieved for all treatments in both studies. The median steady-state plasma APV and RTV concentration-time curves for the three treatments are presented on a linear scale in figures (APV10009) and (APV10010). A summary of steady-state plasma pharmacokinetic parameters and treatment comparisons for APV are presented in tables; the summary for RTV is presented in tables.
APV10009
Co-administration of EFV 600 mg QD with GW433908 1395 mg QD + RTV 200 mg QD (treatment B) decreased plasma APV and RTV exposure. Plasma APV AUCt,ss and Ct,ss were decreased by 13% and 36%, respectively; APV Cmax,ss was unaffected. RTV AUCt,ss, Cmax,ss, and Ct,ss, were decreased by 31%, 16%, and 40%, respectively. However, co-administration of EFV 600 mg QD with GW433908 1395 mg QD + RTV 300 mg QD (treatment C) yielded plasma APV concentrations comparable to treatment A (GW433908 1395 mg QD + RTV 200 mg QD). RTV exposures increased twofold, and were not proportional with the increased RTV dose.
APV10010
Co-administration of EFV 600 mg QD with GW433908 700 mg BID + RTV 100 mg BID (treatment E) resulted in plasma APV AUCt,ss and Cmax,ss values equivalent to those of GW433908 700 mg BID + RTV 100 mg BID without EFV (treatment D) and a minor (17%) reduction in plasma APV Ct,ss. Plasma RTV exposures for treatment E were comparable to those of treatment D. Co-administration of EFV 600 mg QD with GW433908 700 mg BID + RTV 200 mg BID (treatment F) achieved equivalent plasma APV AUCt,ss, Cmax,ss, and Ct,ss values to treatment D (GW433908 1395 mg QD + RTV 200 mg QD). RTV exposures increased 3-5-fold and were not proportional to the increased RTV dose.
Safety analysis
Clinical adverse events
The most commonly reported clinical adverse events, regardless of intensity or relationship to study drug, included those involving the gastrointestinal and nervous systems and the skin. Diarrhea/loose stools and rash were commonly reported for the GW433908 + RTV treatments (treatments A and D). The addition of EFV resulted in dizziness (period 2). No serious adverse events were reported.
APV10009
Of the 32 enrolled subjects, seven prematurely withdrew from the study due to adverse events. Four subjects prematurely withdrew during period 1 (GW433908 + RTV) due to rash (three subjects) or fatigue and joint discomfort (one subject). Three subjects prematurely withdrew during period 2 (GW433908 + RTV + EFV) one each due to an inability to concentrate and unsteady gait, dizziness, or nausea and vomiting. Of the adverse events reported, all but two were of mild or moderate intensity: one case of severe nausea/moderate vomiting and one case of severe rash were reported.
APV10010
Three of the 31 enrolled subjects prematurely withdrew from the study due to adverse events. All three prematurely withdrew during period 1 (GW433908 + RTV) due to rash and pruritus (two subjects) or fatigue, throat irritation, diarrhea, and pruritus (one subject). Of the adverse events reported, all but four were of mild or moderate intensity: one case of severe fatigue and dizziness (treatment E), one case of severe neck pain (treatment F), one case of severe intermittent loose stools (treatment D), and one case of excessive sweating (treatment F) were reported.
Clinical laboratory tests
In both studies, median values were stable for clinical chemistry and hematology parameters with the exception of statistically significant increases in fasting serum total cholesterol and triglyceride concentrations.
APV10009
In contrast to fasting serum total cholesterol concentrations which remained within the range of normal reference values, 11 of 32 subjects had increases in fasting serum triglyceride concentrations from within the range of normal reference values at baseline to above the upper limit of this range (ULN) after study drug administration. The elevations in fasting serum triglyceride concentrations were roughly equivalent to a grade 1 value on the ACTG toxicity grading scale for HIV-infected subjects (ULN to 399 mg/dl).Using the most recent National Cholesterol Education Program (NCEP) criteria for categorizing fasting total cholesterol, 17 subjects would have had high fasting serum total cholesterol concentrations (>= 240 mg/dl) while on treatment, although seven of these had high values at baseline. According to the NCEP guidelines, no subjects had very high fasting serum triglyceride concentrations (>= 500 mg/dl).
APV10010
Among the subjects who completed the study, fasting serum total cholesterol concentrations increased above the normal reference range while on treatment in five of 26 subjects. These fasting serum total cholesterol concentration elevations were equivalent to a grade 1 change on the ACTG toxicity grading scale for HIV-infected subjects (up to 1.3 x ULN). Fasting serum triglyceride concentrations increased above the normal reference range while on treatment in 15 of 26 subjects. These fasting serum triglyceride concentration elevations were equivalent to a grade 1 value in 10 of the subjects and equivalent to a grade 2 value in five of the subjects. Application of the most recent NCEP criteria for categorizing fasting total cholesterol revealed that 15 subjects had high fasting serum total cholesterol concentrations while on treatment, although two of these subjects had high values at baseline. According to the NCEP guidelines, four subjects had very high fasting serum triglyceride concentrations.
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