Compounds or their salts having general formulas (I) and (II) wherein: s=is an integer equal to 1 or 2, preferably s=2; b0=0 or 1; A is the radical of a drug and is such as to meet the pharmacological tests reported in the description, C and C.sub.1 are two bivalent radicals. The precursors of the radicals B and B.sub.1 are such as to meet the pharmacological test reported in the description. ##STR00001##