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O
O
S
S
S
P450
P450
R
2
P
S
CH
2
S
C
2
H
5
R
2
P
S
CH
2
S
C
2
H
5
R
2
P
S
CH
2
S
C
2
H
5
FEMO
O
Phorate
P. sulfoxide
P. sulfone
P450
P450
P450
O
O
O
O
O
R
2
P
S
CH
2
S
C
2
H
5
R
2
P
S
CH
2
S
C
2
H
5
R
2
P
S
CH
2
S
C
2
H
5
O
P. oxon
P. oxon sulfoxide
P. oxon sulfone
R = C
2
H
5
O
Figure 9.4
In vitro oxidative metabolism of phorate by mouse liver enzymes.
insecticide, the neonicotinoids, synthetic chemicals based on nicotine. Imidacloprid is
systemic in both plants and animals; is widely used for agricultural, veterinary, and resi-
dential purposes; and may be the most widely used of all insecticides.
Its mechanism of action involves binding to the nicotinic acetylcholine receptor,
and its metabolism is illustrated in
Figure 9.5
.
Phenylpyrazole Insecticides—Fipronil
Fipronil (chemical name 5-amino-1-[2,6-dichloro-4-(trimethylmethyl)sulfinyl]-1
H
-
pyrazole-3-carbonitrile, CAS No. 120068-37-3) is a member of another relatively new
class of pesticides, the phenylpyrazole insecticides. Fipronil is a widely used, broad-
spectrum insecticide, with applications in crop production and in veterinary practice.
Its mechanism of action involves binding to the GABA receptor. Metabolism in both
surrogate animals and humans consists primarily of oxidation to the sulfone, the only
metabolite produced in mice and by human liver microsomes (
Figure 9.6
). In the latter
case CYP3A4 and CYP2C19 are responsible for essentially all of the activity (
Tang
et al., 2004
).
Pyrethroid Insecticides—Permethrin
Permethrin (chemical name 3-(2,2-dichloroethenyl)-2,2-dimethylcyclopropanecar-
boxylic acid, CAS No. 52645-53-1) is representative of a group of chemicals, the syn-
thetic pyrethroids, whose structures are based on the botanical insecticide pyrethrin.
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