Effects of aztreonam in combination with antipseudomonal antibiotics againstPseudomonas aeruginosa isolated from patients with chronic or recurrent lower respiratory tract infection

The antipseudomonal activity of aztreonam combined with other antibiotics aas examined in vitro to suggest effective therapeutic combinations for the treatment of respiratory tract infections due toPseudomonas aeruginosa. Twenty-fiveP. aeruginosa strains were newly isolated from patients with chronic or recurrent lower respiratory tract infection. The susceptibility of these strains to aztreonam alone and to aztreonam combined with ceftazidime, cefclidin, isepamicin and imipenem was measured using the checkerboard method. The observed MICs suggested that aztreonam alone was not very potent againstP. aeruginosa associated with chronic or recurrent lower respiratory infection, but that cefclidin had strong antipseudomonal activity. The fractionary inhibitory concentration index showed synergy in 60% of theP. aeruginosa clinical isolates with aztreonam plus isepamicin, and antagonism in approximately 16% of strains with aztreonam plus imipenem. When combined with isepamcin, aztreonam may have potent activity against pseudomonal lower respiratory tract infections.