COMPARISON OF THE BACTERICIDAL ACTION OF AMIKACIN, NETILMICIN AND TOBRAMYCIN IN FREE AND LIPOSOMAL FORMULATION AGAINST PSEUDOMONAS-AERUGINOSA

The rates at which free, cationic and anionic liposomal forms of amika cin, netilmicin and tobramycin kill Pseudomonas aeruginosa were studie d in vitro. Control inocula with no antibiotic yielded 6.76, 9.53 and 9.74 log CFU/ml at 0, 6 and 24 h, respectively. Empty anionic or catio nic liposomes had no effect on bacterial growth. The killing rates of free antibiotics against the bacterial strain were not enhanced by the addition of either empty anionic or cationic liposomes. After 6 and 2 4 h of exposure at 1, 2 and 4 times the minimum inhibitory concentrati ons, free amikacin, netilmicin and tobramycin demonstrated a more rapi d bactericidal effect than encapsulated anionic or cationic liposomes. The killing rates of liposomal aminoglycosides were lower than those of free aminoglycosides at identical concentrations, suggesting that o nly fractions of the encapsulated drugs were released from liposomes.