Often not the case - firstly, duodote (pretty common) is atropine & pralidoxime combined in one, and is often given first. Secondly, a single dose of atropine is not typically enough - we’re talking extremely large quantities of atropine, i.e. getting other hospitals to send over their stocks. This answer implies that a single dose is enough. Thirdly, I may be mistaken, but I don’t think atropine involves nicotinic receptors.