Abstract: This disclosure provides a method of treating a bacterial infection in a human patient comprising by administering a therapeutically effective dose of SPR741, a polymyxin analog, in combination with a therapeutically effective amount of an antibiotic other than SPR741. The disclosure establishes 100 mg to 500 mg of SPR741, administered 2 to 4 times daily as the effective amount of SPR741 for co-administration with a therapeutically effective amount of a second antibiotic. The disclosure also provides a method of treating a bacterial infection comprising administering 40 mg/kg patient weight/day or less and preferably 5 mg/kg patient weight/day or less of SPR741 in combination with a therapeutically effective amount of a second antibiotic.