See, there is no such thing! Atropine is not an antidote but rather it serves to treat the symptoms of nerve agent until a hospital can be reached. The automatic injectors are designed to be used by individual soldiers and can be used up to three within 15 minutes. Each soldier is only issued one. Why? Well in the case of a real chemical attack there will be plenty of folks around who won't ever need their injector.... If you can identify the symptoms in yourself (tightness in chest, profuse drooling and postnasal drip and dimness of vision--these three positively ID nerve agent poisoning) well the odds are that you're already dead.
Touche! Point well made!