Principles of concomitant antibiotic therapy.

There are five major disadvantages of the combined use of antibiotics: (i) antibiotic antagonism; (ii) a "false sense of security"; (iii) increased toxicity; (iv) suprainfection; and (v) increased cost. Four situations clearly require the use of antibiotic combinations: (i) to produce antibiotic synergism; (ii) to prevent the emergence of resistant organisms; (iii) to treat mixed infections, such as brain abscess, peritonitis, and pelvic infections; and (iv) to institute therapy for severe infections.