(2S,3R)-2-ethyl-3-(hydroxymethyl)-4-(3-methylimidazol-4-yl)butanoic acid; Pilocarpine Nitrate - Impurity B (EP/BP); (2S,3R)-2-Ethyl-3-(hydroxymethyl)-4-(1-methyl-1H-imidazol-5-yl)butanoic Acid; Pilocarpic Acid, (2S,3R)-2-Ethyl-4-hydroxy-3-((1-methyl-1H-imidazol-5-yl)methyl)butanoic Acid (USP)