Methylnaltrexone bromide73232-52-7100 % similar Naltrexone16590-41-347 % similar Naltrexone hydrochloride16676-29-245 % similar Naloxone hydrochloride357-08-439 % similar Naloxone hydrochloride dihydrate51481-60-838 % similar Nalmefene hydrochloride58895-64-034 % similar