Toxicological Sciences, Vol 48, 189-196, Copyright © 1999 by Society of Toxicology
L Ernstgard, E Gullstrand, G Johanson and A Lof
The aim of this study was to examine if the drug chlorzoxazone has any
influence on the toxicokinetics of acetone and toluene. Chlorzoxazone is
mainly metabolized by the same enzyme (Cytochrome P450 2E1) as ethanol and
many other organic solvents. Ten male volunteers were exposed to solvent
vapor (2 h, 50 watt) in an exposure chamber. Each subject was exposed to
acetone only (250 ppm), acetone + chlorzoxazone, toluene (50 ppm) only,
toluene + chlorzoxazone, and chlorzoxazone only. Chlorzoxazone (500 mg) was
taken as two tablets 1 h prior to solvent exposure. Samples of blood, urine
and exhaled air were collected before, during and until 20 h post exposure.
The samples were analyzed by head-space gas chromatography (acetone and
toluene) and high- performance liquid chromatography (chlorzoxazone, 6-
hydroxychlorzoxazone and hippuric acid). The time-concentration curves of
acetone and toluene in blood were fitted to one- and four- compartment
toxicokinetic models, respectively. Intake of chlorzoxazone was associated
with slight but significant increases in the area under the blood
concentration-time curve (AUC) and steady state concentration of acetone in
blood, along with non significant tendencies to an increased half time in
blood and an increased AUC in urine. Except for a delayed excretion of
hippuric acid in urine, no effects on the toluene toxicokinetics were seen
after chlorzoxazone treatment. Small increases in chlorzoxazone plasma
levels were seen after exposure compared to chlorzoxazone alone. These
interactions, although statistically significant, seem to be small compared
to the interindividual variability on metabolism and toxicokinetics.
ARTICLES
Toxicokinetic interactions between orally ingested chlorzoxazone and inhaled acetone or toluene in male volunteers
Department of Occupational Medicine, National Institute for Working Life, Solna, Sweden. Lena.Ernstgard@niwl.se
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