antibioticsbooks

chapter 19 Polymyxins 143
base colistin), though the actual amount that
is systemically active differs in each patient.
Colistin itself is not used systemically. When
most references refer to “colistin” (including
this one), they are referring to “colistimethate
sodium.”
• To further confound colistin use, different standards
of dosing are used by different countries.
The U.S. formulation is dosed in milligrams,
while Europe and many other countries dose
in international units. When comparing, it is
important to know that 1 mg 5 12,500 units.
• Because polymyxin drugs are generally lastline
antibiotics, they are sometimes used in
combination with other drugs. Various combinations
of colistin and other drugs such
as rifampin may be better than colistin use
alone; this is an area of active study.
• The oral formulation of colistin is given only for
bowel decontamination, such as before GI surgery.
Don’t try to convert someone from IV to
PO colistin to treat a systemic infection.
• Aerosolized colistin is used to decrease colonization
with Gram-negative bacteria (principally
Pseudomonas) in some patients, particularly
those with cystic fibrosis. It should be prepared
just before it is administered. Some experts
have used aerosolized colistin to treat pneumonia
also, though evidence for this practice is not
yet very strong.
What They’re Good For
Polymyxins are useful in the treatment of multidrug
resistant Gram-negative infections including pneumonia,
bacteremia, sepsis, and complicated UTIs.