IN-VITRO SUPPRESSION OF PSEUDOMONAS-CEPACIA AFTER LIMITED EXPOSURE TO SUBINHIBITORY CONCENTRATIONS OF AMILORIDE AND 5-(N,N-HEXAMETHYLENE) AMILORIDE

Amiloride (A) for aerosolized therapy in cystic fibrosis (CF) is under investigation. Antipseudomonal properties of A and A analogs in vitro have recently been described. This study was performed to determine if there was suppression of P. cepacia growth after a limited 2-hour exposure to (subinhibitory) concentrations of A +/- tobramycin m or to the analog 5-(N,N-hexamethylene) amiloride (HMA) in vitro. The MIC of each drug against five different P. cepacia strains was determined. Cells were prepared in Mueller Hinton broth to [10(6)] colony forming units (CFU)/mL and incubated at 35 degrees C for 2 hours in the presence and absence of subinhibitory A, HMA, T, or A + T. The CFU were measured before and at 1-hour intervals after dilutional removal of drug. The post-antibiotic effect (PAE) was defined as the time (in minutes) required for the test culture counts to increase 10-fold minus the time required for control counts to increase 10-fold. At 400 mu g/mL or 200 mu g/mL, the PAE for A against five different strains was 139 +/- 23 and 83 +/- 24 (mean +/- SD) minutes, respectively. For 100 mu g/mL and 50 mu cg/mL HMA, the PAE was 122 +/- 38 and 65 +/- 25 minutes. For T and A + T (200 mu g/mL + 32 mu g/mL) the PAE was 168 +/- 30 and 258 +/- 30 minutes. We conclude that A and the analog HMA in (subinhibitory) concentrations have a suppressive effect on P. cepacia after drug removal and potentiate the effect of T in vitro. (C) 1994 Wiley-Liss, Inc.