McCaughey G et al. - Fosfomycin:tobramycin (F:T)has promising in vitro antimicrobial activity against MRSA and P. aeruginosa with greater activity under anaerobic conditions similar to those found in the cystic fibrosis (CF) lung.

• The antimicrobial activity of a novel 4:1 (w/w) fosfomycin:tobramycin (F:T) combination against CF respiratory pathogens under both aerobic and anaerobic conditions was determined by MIC, time-kill and biofilm studies, and compared with activity of fosfomycin and tobramycin, individually.

• F:T and fosfomycin had excellent activity against P. aeruginosa and were more active than tobramycin against P. aeruginosa under anaerobic conditions with lower MIC50, MIC90 and geometric mean values.
• F:T (p<0.001) and fosfomycin (p<0.001) MICs for P. aeruginosa were significantly lower under anaerobic conditions with tobramycin MICs significantly higher (p<0.001).
• F:T and fosfomycin also had high activity against MRSA with both being more active than tobramycin.
• In time–kill studies, F:T was rapidly bactericidal against all 15 P. aeruginosa and 3/5 MRSA isolates tested.
• F:T also demonstrated bactericidal activity against P. aeruginosa grown in biofilm under both aerobic and anaerobic conditions.