antibioticsbooks

142 PART 2 Antibacterial Drugs
Spectrum
Good: many GNRs, including multidrug resistant
Acinetobacter baumannii, Pseudomonas aeruginosa,
and Klebsiella pneumoniae
Moderate: Stenotrophomonas maltophilia
Poor: all Gram-positive organisms, anaerobes,
Proteus, Providencia, Burkholderia, Serratia,
Gram-negative cocci
Adverse Effects
Renal: The most common adverse effect is nephrotoxicity
due to acute tubular necrosis. Acute
kidney injury commonly occurs in clinical use,
though the incidence of polymyxin-induced toxicity
is hard to estimate because most recent
studies of polymyxins are noncomparative
evaluations of last-line indications in very ill
patients.
Neurological: Neurotoxicity is less common. It can
manifest as dizziness, weakness, paresthesias,
or mental status changes. Neuromuscular blockade
can also occur and may lead to fatal respiratory
arrest.
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Important Facts
• Colistin and polymyxin B are very similar
drugs. Colistin may be more active, but to be
given systemically it is administered as colistimethate
sodium. Colistimethate is then
converted into active colistin in the body.
Colistimethate is renally cleared, and only
the proportion that is not cleared is converted
to colistin. It is dosed as milligrams of active
colistin (~400 mg colistimethate 5 150 mg of