[Colimycin: an old antibiotic which has to be learnt to know].

The emergence of Pseudomonas aeruginosa, Acinetobacter baumanii, and Enterobacteriaceae strains resistant to all beta-lactams (including carbapemenases producing strains), quinolones, aminoglycosides and no new antibiotics have led to reconsider the colimycin use. This antibiotic known since the 50s, had been completely abandoned, in one hand due to poor clinical activity and in other hand because of its toxicity (renal and neurological). The colimycin is an antibiotic complex like no other (until now, we have more questions than answers) and extremely difficult to use. It should be prescribed only when absolutely necessary and only after isolation of the strain responsible of the infection and determination of the in vitro susceptibility tests confirming both resistance to other antibiotics and sensitivity to colimycin. Even if the strain is resistant to other antibiotics, a synergy can be observed with many antibiotics. Monotherapy is not recommended because it promotes rapid development of resistance. Because of low serum concentrations, very close to MICs of targeted bacteria, the dosages are necessarily high.