An Update on the arsenal for multidrug-resistant Acinetobacter infections: Polymyxin antibiotics

OBJECTIVE: To review recent clinical pharmacokinetic and pharmacodynamic data to optimize dosing regimens for polymyxin B and colistin for treatment of infections due to A. baumannii. METHODS: A literature search was performed using the search terms Acinetobacter, polymyxin, colistin, polymyxin B on MEDLINE. Additional references were identified from the resulting citations. RESULTS: Increasing the dose of polymyxin B or colistin and using either in combination with other antibiotic agents demonstrates improved antimicrobial activity against Acinetobacter spp. Polymyxin B, unlike colistin, is available as an active drug and appears to be relatively unaffected by renal function. This is advantageous both for patients with renal impairment and for those with intact renal function. Achieving therapeutic serum concentrations of colistin may be difficult for those with intact renal function due to rapid clearance of the prodrug, colistimethate sodium (CMS). Clinical data are still lacking for polymyxin B, and it remains to be seen whether advantages demonstrated in PK/PD analyses will persist in the larger scale of patient care and safety. CONCLUSIONS: The use of higher doses of either colistin or polymyxin B, as well as combination with other antibiotics, may prevent emerging resistance and preserve the activity of polymyxins against A. baumannii.