Minimum Bactericidal Concentration (MBC)

The minimum bactericidal concentration (MBC) is the lowest concentration in ug/mL of a drug that results in more than 99.9% killing of the bacteria being tested. Indications for determination of bactericidal activity are few, but would include serious infections in immunocompromised patients requiring antibiotic levels lethal to the infecting organism, or infections located in a site that is difficult to reach with antibiotics. Some cases of endocarditis, osteomyelitis, meningitis, and sepsis in neutropenic patients are examples of indications.

Specimen requirements include one plain, red top tube of blood or 3.0 mL of serum. Serum for a peak level should be taken 30 minutes after completion of infusion of an intravenous dose or 60 minutes after an intramuscular dose of the antimicrobial to be assayed. Serum for a trough level should be taken 30 minutes prior to next dose.

A pure culture of the infecting bacteria is also necessary. If the organism is to be submitted, place in a proper mailing container and label as an etiologic agent. Agar plates are acceptable but should not be mailed.

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