In the phase I/II study, PA-457 was administered as a single oral dose to HIV-infected patients who were not on other therapy, in order to determine the pharmacokinetics and antiviral activity of the compound. Single doses of up to 250mg were tested and the level of HIV in the plasma, known as the viral load, was measured before and at intervals after treatment in each patient.
Following dosing, patients in the highest dose groups had reductions in viral load of up to approximately 0.7 log10 and mean reductions compared to the placebo group of around 0.4 log10 that were statistically significant.
Of particular interest were two subjects with pre-existing drug-resistance mutations in the highest dose groups, who both exhibited greater than 0.5 log10 reductions from baseline following PA-457 treatment.
PA-457 was also very well tolerated at all dose levels in the phase I/II study.
“PA-457 exhibited an impressive antiviral effect in this study after only a single dose, providing clear proof-of-concept for the drug and strongly supporting its further development,” commented Dr David Martin, senior vice president of drug development at Panacos.
“In this phase I/II study, PA-457 exhibited a similar effect on viral load to that previously seen with single doses of potent HIV drugs such as the approved drug Viread [marketed by Gilead],” he continued.