Pharmacokinetics/Pharmacodynamics of PA-457 in a 10-day Multiple Dose Monotherapy Trial in HIV-infected Patients
P. Smith, A. Forrest, G. Beatty, J. Jacobson, J. Lalezari, J. Eron, R. Pollard, M. Saag, J. Doto, and D.E. Martin
SUNY-Buffalo School of Pharmacy, UCSF, San Francisco, CA, Beth Israel Medical Center, New York, NY, Quest Clinical, San Francisco, CA, UNC-Chapel Hill, Chapel Hill, NC, UC-Davis, Davis, CA, UAB, Birmingham, AL, Panacos Pharmaceuticals, Inc., Gaithersburg, MD
13th Conference on Retroviruses and Opportunistic Infections, February 2006, Denver, CO
Background: PA-457 is the first in a new class of anti-HIV compounds that inhibit viral maturation by blocking cleavage of CA-SP1. Our purpose was to characterize the pharmacokinetics/pharmacodynamics (PK/PD) of PA-457 when administered as monotherapy to HIV-infected subjects in a Phase II Trial.
Methods: 32 HIV infected adults received 10 days of placebo or oral PA-457 once daily at 25, 50, 100, or 200 mg. A loading dose (double the maintenance dose) was administered on day 1 in all but the 200mg cohort. Plasma viral load and drug concentrations were determined frequently for 21 days. Drug concentrations were assayed by a validated LC/MS/MS method; PK parameters were determined by standard noncompartmental methods. Linear and nonlinear regression was used to evaluate the relationship between antiviral effect and PA-457 drug exposure.
Results: PA-457 was generally well-tolerated. Consistent with previous studies, PA-457 exhibited linear pharmacokinetics, with a long mean (CV%) half-life of 62.7 (19%) hours. The mean (CV%) oral clearance was 0.21 (28) L/h. Compared to baseline values, the median (range) Log10 reduction in viral load on Day 11 was 0.046 (-0.505, 0.149), -0.174 (-0.589, 0.048), -0.483 (-0.874, 0.295) and -1.05 (-1.62, -0.071) for the 25, 50, 100, & 200 mg doses, respectively. Both AUC and trough concentrations were highly associated with antiviral response (p<0.01 for each), with greater activity observed with increasing drug exposure. Based on the study design, AUC and trough concentrations were highly correlated (r2 0.99), and could not be differentiated as predictors of response. The maximum antiviral effect (Emax) for PA-457 was not observable at the highest dose level.
Conclusions: PA-457 demonstrated significant antiviral activity at the higher dose levels, with greater activity observed with increasing drug exposure. Additional antiviral activity is likely with doses higher than those used in this trial, as Emax was not reached at 200mg. Similar to other available antiretrovirals, PK/PD appears to be an important determinant of PA-457 activity. Additional studies to evaluate the potential role of PA-457 in the treatment of HIV-infection are warranted.<<
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