Analgin

CAS 5907-38-0

CAS 5907-38-0 identifies metamizole sodium monohydrate, commonly associated with the names Analgin and dipyrone. It differs from the anhydrous sodium salt, CAS 68-89-3, by one water molecule per formula unit. That changes formula mass and the interpretation of a weighed amount, making the calculation basis important in pharmaceutical analysis. Reference standards specify a material for measurement rather than automatically supplying a finished medicine. Solution transformation adds another consideration: the original solid and the species measured after dissolution are not always the same analytical question. Hydration state also does not remove metamizole's important agranulocytosis risk. This entry illustrates why common names, exact solid form, analytical purpose, and medicinal safety should each be described clearly rather than treated as interchangeable pieces of information.