Final answer:
Lewisite casualties are treated with an anticholinergic to manage symptoms and an oxime as an antidote, often administered through an autoinjector like the ATNAA for immediate action in field conditions.
Step-by-step explanation:
The recommended treatment for a Lewisite casualty involves a combination of an anticholinergic and an oxime. Anticholinergics are used to mitigate the symptoms by reducing the effects of acetylcholine, a neurotransmitter that becomes overly abundant due to the poisoning. Oximes are employed as an antidote; they work by displacing phosphate molecules from the active site of cholinesterase enzymes, which in turn allows for the proper breakdown of acetylcholine, easing the symptoms. This combination is typically provided to military personnel in the form of an autoinjector, such as the ATNAA (Antidote Treatment Nerve Agent Auto-Injector), which is designed for easy use under stressful conditions.