novel 7 - piperazino and 7 - n - methylpiperazino derivatives of 5 - amino - 1 - cyclopropyl - 6 , 8 - dihydro - 1 , 4 - dihydro - 4 - oxoquinoline - 3 - carboxylic acids as antibacterial agents are described as well as methods for their manaufacture , formulation , and use in treating bacterial infections .