Warning on Colistimethate for Inhalation

FDA is investigating a patient death that may be associated with the inhalation of the antibiotic colistimethate, or Coly-Mycin M. This drug is used to treat serious infections due to Gram-negative bacteria, particularly Pseudomonas aeruginosa. It is approved only for intravenous or intramuscular injection, but some practitioners prescribe it off-label as a solution to be inhaled from a nebulizer. The solution is prepared by mixing the drug with sterile water or saline just prior to inhalation.

Colistimethate is a pro-drug that is inactive in its dry state. When mixed with water, it undergoes spontaneous hydrolysis to the bioactive form, colistin, which may cause pulmonary inflammation. Storing the pre-mixed colistimethate solution for longer than 24 hours results in increased concentrations of colistin, and this may increase the potential for lung toxicity.

In the case FDA is investigating, a cystic fibrosis patient had a home nebulizer treatment with a colistimethate solution that had been pre-mixed by a pharmacy. The patient developed acute respiratory failure and later died.

There are three important precautions that may help to prevent this kind of toxicity:

• First, if you choose to prescribe colistimethate for inhalation, avoid pre-mixed, ready-to-use solutions.

• Second, instruct patients and caregivers to administer the solution promptly after it's mixed.

• Finally, instruct patients who may have supplies of the pre-mixed form to discard them.

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