Oximes:
Obidoxime and Pralidoxime |
| Agents
targetted |
G- and
V-type nerve agents |
| Generally
effective against |
Used
in the treatment of poisoning by organophosphate insecticides such
as malathion
and diazinon. |
| Available
forms |
Usually
supplied as injectable aqueous solutions. Nerve agent antidote kits
include autoinjectors for immediate self-administration. Prophylactic
oximes, specifically pyridostigmine bromide, are taken as tablets.
|
| Indications
and usage |
Used
in cases of organophosphate poisoning, either on the battlefield or
in known cases of exposure to organophosphorus insecticides. |
| Contraindications |
Oximes
are used by titrating the victim, in much the same way as atropine
is used, and under the circumstances, contraindications are almost
a secondary consideration. However, kidney disease and myasthenia
gravis are contraindications for oxime treatment of insecticide
poisoning. The selection of the oxime is highly dependent upon the
agent involved as some oximes are ineffective against some agents.
Obidoxime is considered ineffective against soman and cyclosarin.
Four oximes are currently considered suitable for treatment of nerve
agent poisoning. In addition to obidoxime and pralidoxime, two Hagedorn
oximes, HI-6 and Hlö7, are also considered effective. Their
relative effectiveness against primary chemical agents is shown
below.
| Relative
effectiveness of oximes in reactivating nerve agent-inactivated
cholinesterases |
| Agent |
Relative
effectiveness |
| GB (Sarin) |
Ob
= Pr = HI-6 = Hlö7 |
| |
Ob>Hlö7>HI-6>Pr |
| GD (Soman) |
Hlö7>HI-6>>Pr>>Ob
|
| GA (Tabun) |
Hlö7
= Ob > HI-6 >> Pr |
| |
Ob> Hlö7>Pr>>HI-6 |
| GF (Cyclosarin) |
Hlö7 = HI-6
> Pr >> Ob |
| VX |
Ob
= Pr = HI-6 = Hlö7 |
| VR |
Hlö7>HI-6>Ob>>Pr |
| Note:
these relationships are drawn from animal and laboratory studies
and should not be applied to use in humans. |
| Ob = obidoxime,
Pr = Pralidoxime |
|
|
| Drug
interactions |
Caffeine-like
stimulants (aminophylline, caffeine, and theophylline) can exacerbate
the effects of the oximes. |
| Adverse
reactions and side effects
NOTE:
all such reactions are rare. |
Adverse
effects seen in healthy subjects include dizziness, visual problems,
and nausea. |
| Mode
of action |
Oximes
react with the nerve agent after it has bound to the acetylcholinesterase.
The reaction product is unstable and is rapidly broken down in the
body. Oximes are also inhibitors of acetylcholinesterase, but they
are reversible and can sequester some of the acetylcholinesterase
and protect it from inactivation by the nerve agent.
|
| Structure |
| Obidoxime chloride |
Pralidoxime chloride |
 |
 |
|
| Chemical
names |
- 1,1'-(Oxydimethylene)bis(4-formylpyridinium)
dioxime (Obidoxime chloride)
- 2-[(hydroxyimino)methyl]-1-methylpyridinium
chloride (Pralidoxime chloride)
|
| CAS
Registry number |
- 7683-36-5 (Obidoxime
chloride)
- 51-15-0 (Pralidoxime
chloride)
|
Synonyms
and trade names
(known
and reported, not all may be current.) |
| |
Trade
Name |
|
| Obidoxime chloride |
Pralidoxime chloride |
- Pirrangit
- Toxobindin
- Toxogonin
|
- ComboPen
- 2-PAM chloride
- Protopam
|
|