Mary Beth Wire

Phase I Dose Escalation Trial Evaluating the Pharmacokinetics, Anti-Human Cytomegalovirus (HCMV) Activity, and Safety of 1263W94 in Human Immunodeficiency Virus-Infected Men with Asymptomatic HCMV Shedding

ABSTRACT 1263W94 [maribavir; 5,6-dichloro-2-(isopropylamino)-1,β-l-ribofuranosyl-1-H-benzimidazole] is a novel benzimidazole compound for treatment of human cytomegalovirus (HCMV) infection and disease, with potent in vitro activity against HCMV and good oral bioavailability. A phase I study was conducted to determine the pharmacokinetics (PK), anti-HCMV activity, and safety of 1263W94 administered as multiple oral doses to human immunodeficiency virus type 1-infected adult male subjects with asymptomatic HCMV shedding. Subjects received one of six dosage regimens (100, 200, or 400 mg three times a day, or 600, 900, or 1,200 mg twice a day) or a placebo for 28 days. 1263W94 demonstrated linear PK, with steady-state plasma 1263W94 profiles predictable based on single-dose data. 1263W94 was rapidly absorbed following oral dosing, and values for the maximum concentration of the drug in plasma and the area under the concentration-time curve increased in proportion to the dose. 1263W94 demonstrated in vivo anti-HCMV activity in semen at all of the dosage regimens tested, with mean reductions in semen HCMV titers of 2.9 to 3.7 log10 PFU/ml among the four regimens evaluated for anti-HCMV activity. 1263W94 was generally well tolerated; taste disturbance was the most frequently reported adverse event over the 28-day dosing period.

Phase I Safety and Pharmacokinetic Trials of 1263W94, a Novel Oral Anti-Human Cytomegalovirus Agent, in Healthy and Human Immunodeficiency Virus-Infected Subjects

ABSTRACT 1263W94 [maribavir; 5,6-dichloro-2-(isopropylamino)-1, β-l-ribofuranosyl-1-H-benzimidazole], a novel benzimidazole compound, has been demonstrated to potently and selectively inhibit human cytomegalovirus replication in vitro and to have favorable safety profiles in animal species. Two phase I trials evaluated the safety and pharmacokinetics of escalating single doses of 1263W94 in 13 healthy subjects (dose, 50 to 1,600 mg) and 17 human immunodeficiency virus (HIV)-infected subjects (dose, 100 to 1,600 mg). No severe safety concerns were observed in the evaluation of adverse events, vital signs, electrocardiograms, and clinical laboratory tests following administration of a single dose of 1263W94. The most frequently reported adverse events in both populations were taste disturbance (80%) and headache (53%). 1263W94 was rapidly absorbed following oral administration, with peak concentrations in plasma (Cmax) occurring 1 to 3 h after dosing. The increases in the Cmax of 1263W94 and the area under the concentration-time curve from time zero to infinity (AUC0-∞) for 1263W94 were dose dependent; Cmax increased slightly less than proportionally to the dose, and AUC0-∞ increased slightly more than proportionally to the dose. 1263W94 was rapidly eliminated, with a mean half-life in plasma of 3 to 5 h; the half-life was independent of the dose level. Less than 2% of the 1263W94 dose administered was eliminated unchanged in urine. The principal metabolite of 1263W94 was 4469W94 (which is derived by N-dealkylation of 1263W94 via CYP3A4), which accounted for 30 to 40% of the dose in urine. Greater than 98% of the 1263W94 in plasma is bound to proteins, and the extent of binding appears to be constant over the dose range of 200 to 1,600 mg. In the trial with HIV-infected subjects, consumption of a high-fat meal decreased the 1263W94 AUC0-∞ and Cmax in plasma by ∼30%.

Fosamprenavir : clinical pharmacokinetics and drug interactions of the amprenavir prodrug.

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.

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

ABSTRACT This study compared the plasma amprenavir pharmacokinetics of the human immunodeficiency virus (HIV) protease inhibitors amprenavir (Agenerase) 1,200 mg twice daily (BID) and the amprenavir prodrug GW433908, a formulation that substantially reduces the number of tablets per dose compared with amprenavir, at doses of 1,395 mg and 1,860 mg BID, in combination with abacavir 300 mg BID and lamivudine 150 mg BID in patients with HIV infection. Overall, 78 patients received study treatment. Compared with amprenavir 1,200 mg BID, both GW433908 1,395 mg BID and GW433908 1,860 mg BID delivered equivalent steady-state (ss) values for area under the plasma amprenavir concentration-time curve (AUC) at the end of a dosing interval (τ), lower maximum plasma amprenavir concentrations (30% lower), and higher plasma amprenavir concentrations at the end of a dosing interval (28% higher for GW433908 1,395 mg BID and 46% higher for GW433908 1,860 mg BID). Time-variant plasma amprenavir pharmacokinetics were observed with reductions in plasma amprenavir exposure over the first 4 weeks of dosing; the decrease in plasma amprenavir AUCτ,ss versus the AUC from 0 h to ∞ was 27% for GW43308 1,395 mg, 45% for GW433908 1,860 mg, and 23% for amprenavir 1,200 mg. All three regimens reduced plasma HIV-1 RNA (∼2 log10 copies/ml) and increased CD4+ cell counts (∼100 cells/mm3) over the initial 28 days. Adverse event profiles were consistent with those previously reported for amprenavir. Although not statistically tested, the GW433908 groups appeared to have fewer gastrointestinal symptoms. In conclusion, the protease inhibitor GW433908 delivered comparable plasma amprenavir concentrations to those delivered by amprenavir 1,200 mg BID. GW433908, in combination with abacavir and lamivudine, demonstrated potent antiviral activity and was generally well tolerated over a 4-week period.

Pharmacokinetics and safety of GW433908 and ritonavir, with and without efavirenz, in healthy volunteers

Objective: To evaluate the safety and pharmacokinetic interaction between GW433908, ritonavir (RTV), and efavirenz (EFV). Methods: 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. Results: 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. Conclusion: 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.

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 qdwith 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, &tgr;[AUC(0-&tgr;)], 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.

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

ABSTRACT 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-τ), and trough concentrations (Cτ) 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-τ (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 Cτ 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 Cτ observed during the 100-mg QD period being nearly threefold higher. The GLS mean APV Cτ was 2.5 times higher than the historical Cτ 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.

Pharmacokinetics of fosamprenavir plus ritonavir in human immunodeficiency virus type 1-infected adult subjects with hepatic impairment.

ABSTRACT The effect of hepatic impairment on fosamprenavir/ritonavir pharmacokinetics was investigated. Sixty human immunodeficiency virus type 1-infected subjects, including 13, 20, and 10 subjects with mild, moderate, and severe hepatic impairment, respectively, and a comparator group of 17 subjects with normal hepatic function, were enrolled. Subjects with normal hepatic function received fosamprenavir at 700 mg plus ritonavir at 100 mg twice daily, whereas subjects with hepatic impairment received adjusted doses in anticipation of increased exposures. For subjects with mild hepatic impairment, the studied regimen of fosamprenavir 700 mg twice daily plus ritonavir 100 mg once daily delivered 17% higher values for the maximum plasma amprenavir concentration at the steady state (Cmax), 22% higher values for the area under the plasma concentration versus time curve over the dosing interval at the steady state [AUC(0-τ)], similar values for the concentration at the end of the dosing interval (Cτ), and 114% higher unbound Cτ values. For subjects with moderate hepatic impairment, the studied dosage regimen of fosamprenavir at 300 mg twice daily plus ritonavir at 100 mg once daily delivered 27% lower plasma amprenavir Cmax values, 27% lower AUC(0-24) values, 57% lower Cτ values, and 21% higher unbound amprenavir Cτ values. For subjects with severe hepatic impairment, the studied dosage regimen of fosamprenavir at 300 mg twice daily plus ritonavir at 100 mg once daily delivered 19% lower plasma amprenavir Cmax values, 23% lower AUC(0-24) values, 38% lower Cτ values, and similar unbound amprenavir Cτ values. With a reduced ritonavir dosing frequency of 100 mg once daily, the plasma ritonavir AUC(0-24) values were 39% lower, similar, and 40% higher for subjects with mild, moderate, and severe hepatic impairment, respectively. The results of the study support the use of reduced fosamprenavir/ritonavir doses or dosing frequencies in the treatment of patients with hepatic impairment. No significant safety issues were identified; however, plasma amprenavir and ritonavir exposures were more variable in subjects with hepatic impairment, and those patients should be closely monitored for safety and virologic response.

Ritonavir Increases Plasma Amprenavir (APV) Exposure to a Similar Extent when Coadministered with either Fosamprenavir or APV

ABSTRACT 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.

Pharmacokinetics and 48-week Safety and Antiviral Activity of Fosamprenavir-containing Regimens in HIV-infected 2- to 18-year-old Children

Background: Pharmacokinetics, safety and antiviral activity of twice-daily fosamprenavir with or without ritonavir were evaluated in 2- to 18-year-old protease inhibitor–naïve and -experienced HIV-1–infected children. Methods: Serial pharmacokinetic samples were collected at week 2 and predose samples every 4–12 weeks. Safety and plasma HIV-1 RNA were monitored every 4–12 weeks. Results: Twenty protease inhibitor–naïve 2- to <6-year-old subjects received antiretroviral treatment including unboosted fosamprenavir twice-daily, whereas 89 protease inhibitor–naïve and -experienced 2- to 18-year-old subjects received fosamprenavir/ritonavir-containing therapy twice-daily. Median fosamprenavir exposure was 891 days (range 15–1805 days), with 88% exposed >48 weeks. Twice-daily doses of fosamprenavir/ritonavir 23/3u2009mg/kg in 2- to <6-year olds, 18/3u2009mg/kg in ≥6-year olds and 700/100u2009mg in adolescents achieved plasma amprenavir exposures comparable with or higher than 700/100u2009mg twice-daily in adults while fosamprenavir 30u2009mg/kg twice-daily in 2- to <6-year olds led to exposures higher than 1400u2009mg twice-daily in adults. The proportion of subjects with HIV-1 RNA <400 copies/mL at week 48 was 60% for fosamprenavir and 53–74% for fosamprenavir/ritonavir (intent-to-treat [exposed], snapshot analysis). Median increases in absolute and relative (percentage) CD4 counts from baseline to week 48 occurred in both the fosamprenavir (340 cells/mm3; 8%) and fosamprenavir/ritonavir group (190 cells/mm3; 8%). The most common adverse events were vomiting, cough, and diarrhea; 18 subjects experienced serious adverse events, including 9 with suspected abacavir hypersensitivity. Conclusions: Fosamprenavir regimens administered to HIV-1–infected children aged 2–18 years were generally well-tolerated and provided sustained antiviral activity over 48 weeks, with plasma amprenavir exposures comparable with or higher than adults.