It suspect it was a sulfa drug...
To quote the US Army Military History Institute ---
"SULFA DRUGS
Sulfonamides, available since the mid-1930s, became widely used in the U.S. Army during WWII. Each individual soldier's first aid kit contained a package of sulfa powder (syulfanilamide) for dusting on open wounds..." I would guess the medics carried lots of this with them in their medkits.
My source is the ww2.doc file at this link
http://carlisle-www.army.mil/usamhi/...phies/medical/