How do I use the MIC to determine what antibiotic to use?

Let’s say you order sensitivities for an organism thought to be causing a UTI and you get:

URINE CULTURE:
ESCHERICHIA COLI. 10,000-100,000 ORGANISMS/ML..
Cefazolin interpretative criteria are based on a dosage regimen of 2g every 8h.

SENSITIVITIES: MIC expressed in MCG/ML
AMPICILLIN————=>32 R
AMPICILLIN/SULBACTAM– 16 I
CEFAZOLIN————- <=4 S
CEFEPIME————– <=1 S
CEFTAZIDIME———– <=1 S
CEFTRIAXONE———– <=1 S
CIPROFLOXACIN——— =>4 R
GENTAMICIN———— <=1 S
MEROPENEM————- <=0.25 S
NITROFURANTOIN——– <=16 S
PIPERACILLIN/TAZO—– <=4 S
TETRACYCLINE———- =>16 R
TOBRAMYCIN———— <=1 S
TRIMETHOPRIM/SULFA—- =>16 R
VANCOMYCIN———— 1 S

The MIC (minimum inhibitory concentration) is a measurement of how much antibiotic is required to stop growth of an organism. The smaller the number is, the more effective the antibiotic is. Generally speaking, the smaller the MIC, the more likely it is to treat the infection and prevent resistance from developing.

However, be warned that the drug with the smallest MIC does not always win–this Medscape article explains that MIC is calculated differently for different drugs depending on whether they are concentration or time-dependent, so the MIC for say, Cipro and Zosyn may not be directly comparable. Also, some drugs will not penetrate certain sites–for instance, nitrofurtantoin (Macrobid) is frequently used for uncomplicated UTIs but cannot be used to treat pyelonephritis because of its penentration.

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s