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Antimicrobial Agents and Chemotherapy, 03 1996, 642-645, Vol 40, No. 3
P Rajagopalan, FD Boudinot, CK Chu, BC Tennant, BH Baldwin and RF Schinazi
The woodchuck (Marmota monax) has proven to be a suitable animal model for
studying hepatitis B virus (HBV) infection owing to similarities in the
course of infection between woodchuck hepatitis virus (WHV) in woodchucks
and HBV in humans. (-)-beta-L-2',3'-Dideoxy-3'-thiacytidine (3TC;
lamivudine) is a nucleoside analog which has demonstrated antiviral
activity against HBV as well as human immunodeficiency virus (HIV). The
purpose of the present investigation was to characterize the
pharmacokinetics of 3TC following intravenous and oral administration of 20
mg of 3TC per kg of body weight to woodchucks. Following intravenous
administration, the concentrations of 3TC in plasma declined, with a
terminal half-life of 2.84 +/- 0.85 h (mean +/- standard deviation). The
systemic clearance and steady-state volume of distribution of 3TC were 0.22
+/- 0.078 liters/h/kg and 0.75 +/- 0.13 liters/kg, respectively. The renal
clearance of the nucleoside analog was 0.063 +/- 0.016 liters/h/kg. The
oral bioavailability of 3TC ranged from 18 to 54%. Allometric relationships
between pharmacokinetic parameters and body weight developed by Hussey et
al. (E.K. Hussey, K.H. Donn, M.J. Daniel, S.T. Hall, A.J. Harker, and G.L.
Evans, J. Clin. Pharmacol. 34:975-977, 1994) were augmented by including
data from woodchucks, monkeys (S.M. Blaney, M.J. Daniel, A.J. Harker, K.
Godwin, and F.M. Balis, Antimicrob. Agents Chemother. 39:2779-2782, 1995),
and additional data from rats (P. Rajagopalan, L. Moore, C.K. Chu, R.F.
Schinazi, and F.D. Boudinot, submitted for publication). Interspecies
scaling of the pharmacokinetic parameters of 3TC demonstrated a good
correlation between clearance (0.74 . W0.76 [where W is body weight]; r =
0.93; P < 0.025), apparent volume of distribution (1.62 . W0.81; r =
0.98; P < 0.005), and steady-state volume of distribution (1.09 . W0.94;
r = 0.99; P < 0.05) and species body weight. The allometric
relationships for clearance and volume of distribution at steady state
predicted the observed pharmacokinetic parameters in humans quite well;
however, the apparent volume of distribution was underestimated in humans.
Thus, the pharmacokinetic data obtained with the woodchuck HBV animal model
should be useful for designing clinical trials.
Copyright © 1996 by the American Society for Microbiology. All rights reserved.
Pharmacokinetics of (-)-2'-3'-dideoxy-3'-thiacytidine in woodchucks
Department of Pharmaceutics, University of Georgia, Athens 30602, USA.
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