In order to obtain 3-(dimethylamino)-1-hydroxypropylidene-1,1-bisphosphonic acid (II), transfer 3-(dimethylamino)propionitrile (I) to a reactor, add water and PCl3; then slowly add POCl3 and finally water. Filter with reduced pressure and wash the solid with methanol. Place in an oven with forced air circulation until the solid is dry. To obtain the sodium salt (III) add NaOH to acid (II), filter, add methanol and dry in an oven with forced air circulation until constant weight. The 3-(dimethylamino)-1-hydroxypropylidene-1,1-bisphosphonic acid monosodium salt (III) is then obtained.