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Positive Phase I/II Data of IDX899 Confirm Potent Antiviral Activity and Favorable Safety Profile in Treatment-Naive HIV-Infected Patients

Thursday, June 12, 2008 General News J E 4
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CAMBRIDGE, Mass., June 12 IdenixPharmaceuticals, Inc. (Nasdaq: IDIX), a biopharmaceutical company engaged inthe discovery and development of drugs for the treatment of human viral andother infectious diseases, today reported phase I/II data for IDX899, anon-nucleoside reverse transcriptase inhibitor (NNRTI) being developed for thetreatment of HIV-1. Patients receiving once-daily IDX899 achieved a meanplasma viral load reduction of approximately 1.8 log(10) after seven days oftreatment in each of the 800 mg, 400 mg and 200 mg dosing cohorts. Patientsreceiving placebo had a 0.05 log10 viral load increase over the same treatmentperiod. No treatment-related serious adverse events were reported for any ofthe patients receiving IDX899 and no patients discontinued the study. Also,there were no discernable patterns in adverse events between treatment groupsand there were no laboratory abnormalities during the treatment period. Thesedata demonstrate potent antiviral activity and a favorable safety profile atall tested doses.

"The profound inhibition of HIV-1 virus replication of IDX899 at doses of400 and 200 mg daily confirm the potent antiviral activity previously reportedat higher doses," said Dr. Robert Murphy, John P. Phair Professor ofInfectious Diseases, Director, Global Health Research, Feinberg School ofMedicine, Northwestern University. "These early clinical data are veryencouraging, showing that IDX899 offers potent viral suppression combined witha promising safety profile."

Study Design

The phase I/II clinical trial was designed to evaluate the safety,tolerability, antiviral activity and pharmacokinetics of IDX899. Three cohortsof 800 mg/day, 400 mg/day and 200 mg/day were completed with ten HIV-1-infected treatment-naïve patients randomized 8:2 in each cohort to receiveorally once-daily IDX899 or matching placebo, respectively, for seven days.Based on the potent antiviral activity of IDX899 seen to date, the study wasrecently amended to also evaluate a lower dose of 100 mg/day.

Study Results

Patients receiving daily oral administration of 800 mg, 400 mg and 200 mgIDX899 achieved mean viral load reductions of 1.78, 1.78, and 1.83 log(10),respectively, after seven days of treatment based on results determined by theRoche Amplicor(R) 1.5 assay. Patients (n=6) receiving placebo achieved meanplasma viral load increase of 0.05 log(10).

One key eligibility criterion for enrollment in the study was thatpatients' CD4+ count (or T-cell count) had to be greater than or equal to 200cells/mm3. The mean CD4+ count change from baseline increased by at least 60cells/mm3 for each of the 800 mg, 400 mg and 200 mg dosing cohorts anddecreased by about 80 cells/mm3 for patients receiving placebo. No clearpharmacokinetic/pharmacodynamic relationship was demonstrated, likely due todrug trough levels well above the EC(90) of IDX899 against wild-type HIV-1.

"We believe any new HIV treatment must demonstrate potent antiviralactivity at low doses to be suitable for combination therapy and possibleco-formulation with other antiretroviral drugs. We are very encouraged thatthe robust antiviral activity observed at 800 mg/day was also achieved by the400 and 200 mg/day cohorts," said Douglas Mayers, M.D., Idenix's chief medicalofficer. "We look forward to evaluating a 100 mg once-daily IDX899 dose inthe upcoming weeks."

Data for patients enrolled in the study will be presented today at theXVII International HIV Drug Resistance Workshop in Sitges, Spain.

About Idenix

Idenix Pharmaceuticals, Inc., headquartered in Cambridge, Massachusetts,is a biopharmaceutical company engaged in the discovery and development ofdrugs for the treatment of human viral and other infectious diseases. Idenix'scurrent focus is on the treatment of infections caused by hepatitis C virusand HIV. For further information about Ideni
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