Vol. 31, Issue 2, 147-152, February 2003

SHORT COMMUNICATION
Pharmacokinetics and Metabolism of the Reactive Oxygen Scavenger -Phenyl-N-tert-butylnitrone in the Male Sprague-Dawley Rat

Mary E. Trudeau-Lame, Amit S. Kalgutkar, and Michael LaFontaine

Pharmacokinetics, Dynamics, and
Metabolism,
Pfizer Global Research & Development,
Groton, CT (M.E.T.-L., A.S.K.);
Central Connecticut State University,
New Britain, CT (M.E.T.-L., M.L.)

The pharmacokinetics of the spin-trap -phenyl-N-tert-butylnitrone (PBN) was investigated in male Sprague-Dawley rats. Plasma concentrations after i.v. administration (10 mg/kg) declined monoexponentially with a terminal half-life of 2.01 ± 0.35 h and total plasma clearance (CL_p) and volume of distribution at steady state (Vd_ss) averaged 12.37 ± 3.82 ml/min/kg and 1.74 ± 0.5 l/kg, respectively. The observed CL_p was in close agreement with the blood clearance (CL_b) value (11.5 ml/min/kg) predicted from in vitro liver microsomal incubations suggesting that PBN CL_p in rats is predominantly due to hepatic metabolism. Peak plasma concentration (C_max) following p.o. (20 mg/kg) and s.c. (30 mg/kg) PBN administration was 7.35 ± 1.92 and 3.56 ± 0.66 µg/ml, whereas the area under the concentration-time curve from 0 to infinity was 23.89 ± 5.84 and 15.96 ± 3.10 µg-h/ml, respectively. The mean oral bioavailability of PBN was 85.63 ± 20.93%. Biotransformation studies indicated the P450 2C11-catalyzed hydroxylation of PBN to M1. Potential sites of hydroxylation included the benzylic carbon resulting in phenyl-N-tert-butylhydroxamic acid or the phenyl ring that would afford -hydroxyphenyl-N-tert-butylnitrone (HOPBN). The structure of M1 was established as -4-Hydroxyphenyl-N-tert-butylnitrone (4-HOPBN) on the basis of: 1) obvious LC R_t differences between M1 and the authentic hydroxamate standard, 2) P450 catalyzed hydroxylation of [²H]PBN that contained a deuterium instead of a hydrogen atom on its benzylic position and which afforded [²H]M1, and 3) comparison of the liquid chromatography-tandem mass spectrometry properties with a synthetic 4-HOPBN standard. We speculate that 4-HOPBN is an "active" PBN metabolite that provides an additive effect to the pharmacological action of PBN in vivo.