nsisting of H and C1-3 alkyl; R1 represents a substituent selected from the group consisting of --PO3 H2, and ##STR5## R2 represents a substituent selected from the group consisting of ##STR6## with the proviso that when R1 is --PO3 H2, R2 is other than H or C1-3 alkyl; and the pharmaceutically-acceptable water-soluble salts of the above acids; and (B) a pharmaceutically acceptable water-soluble s