Which of the following provides the best explanation for neostigmine being preferred over physostigmine for treating myasthenia gravis?: (A) It is better absorbed orally, (B) It has longer duration of action, (C) It has additional direct agonistic action on nicotinic receptors at the muscle end plate, (D) It penetrates blood brain barrier
Answer is C. Neostigmine is a quaternary ammonium derivative and is water soluble. Its absorption from GIT and penetration in the brain and cornea is much less than physostigmine. It produces additional action on NM receptors.