CrCl > 80: 2.5-5 mg/kg/day IM or IV in 2 to 4 divided doses, maximum 5 mg/kg/day. 1 million units bid inhaled has been used to treat multidrug resistant pneumonia (PubMed).
Comes as an inactive prodrug that has to be metabolized to colistin. Much of the prodrug is cleared by the kidneys before it is converted but is converted in the urine so good for UTI. Great patient variability in blood levels.
Higher dose (9 MIU vs 4 MIU) did not decrease mortality but did increase nephrotoxicity (PubMed).
CrCl 80-50: 75% of the normal dose.
CrCl 50-10: 50% of the normal dose.
CrCl < 10: 25% of the normal dose.
The above is US dosing. European dosing has higher doses at lower gfr and is better.
Important side effects
Neurotoxic (confusion, muscle weakness, visual disturbances, vertigo, paraesthesia, neuropathy) and nephrotoxic (about half will develop some degree of renal insufficiency, esp at higher doses (PubMed)).
Important drug interactions
Alcuronium, amikacin, atracurium, cisatracurium, doxacurium, fazadinium, gallamine, hexafluorenium, metocurine, mivacurium, pancuronium, pipecuronium, rapacuronium, rocuronium, tubocurarine, vecuronium.
Inhaled colistin can be fatal or cause ARDS.
Rants and Screeds
There are issues with purity and potency due to the way the antibiotic is produced that cannot be predicted (PubMed).
May be using more of it as resistance rates keep on going up.
Treatment of choice
Aerobic gram negative rods including Acinetobacter, Citrobacter, Haemophilus influenzae, Enterobacter, Escherichia coli, Klebsiella, Morganella morganii, Pseudomonas aeruginosa, Salmonella, Shigella, Stenotrophomonas maltophilia, Yersinia pseudotuberculosis.
For hospital acquired pneumonias, it is probably no worse than 'usual' antibiotics (PubMed).
Resistance, unfortunately plasmid mediated, is starting to be seen as of 2016.
Don't use for
Pseudomonas mallei, Burkholderia cepacia, Proteus species, Providencia species, Serratia species, Edwardsiella species, and Brucella species are all resistant to colistin.
Detergent. But it will get out those pesky grass stains.