Atropine methyl (bromide)

Atropine methyl bromide (Methylatropine bromide), an antagonist of muscarinic acetylcholine receptors (mAChR), is a quaternary ammonium salt of atropine and an active molecule used for pupil dilation during ophthalmic examinations. Due to its high polarity, it is used to relieve pyloric spasm in infants. It is less likely than atropine to cross the central nervous system^[1][2]. In Vivo:Atropine methyl bromide (2.5 mg/kg; nasal; 40 pulses over 1 min) provides 100% survival against lethal sarin inhalation exposure in guinea pigs, while normalizing peripheral cholinergic, respiratory, cardiac, and biochemical toxic effects^[1].
Atropine methyl bromide (15-20 mg/kg; i.p.; single injection prior to behavioral run; 50 μg/rat; hippocampal; single injection prior to behavioral run) produces significant impairments in complex operant conditioning task performance in rats when administered directly into the hippocampus at 50 μg/rat (unilateral or bilateral), but only produces a single significant behavioral change at the highest tested intraperitoneal dose of 20 mg/kg^[2].