In order to determine the optimal dose, drug exposure (ie, PK) is correlated to the antimicrobial effect (ie, PD). Introduction to pharmacokinetics. PK and PD are often linked and summarized to form the PK/PD index. The most commonly employed PK/PD indices are the ratio of free drug area under the curve (AUC) over 24 hours to minimum inhibitory concentration (MIC) (fAUC0–24/MIC), the percentage of the dosing interval in which the free concentration of the antibiotic exceeds the MIC (% ft.MIC), and the ratio of free maximal concentration to MIC (fCmax/MIC). Studies confirm that the magnitude of the PK/PD index predicts the microbiological effect for a given drug class and a given pathogen group, as measured by inhibition (static effect) or by reduction of the bacterial load by 1, 2, 3, or more log10 steps. The discriminative power of the magnitude of PK/PD indices in differentiating outcomes has been shown in vitro and in animals as well as in human patients (U. Theuretzbacher, CID 2012)

PKPD index

More information: Mouton JW, Ambrose PG, Canton R, Drusano GL, Harbarth S, MacGowan A, Theuretzbacher U, Turnidge J.: Conserving antibiotics for the future: new ways to use old and new drugs from a pharmacokinetic and pharmacodynamic perspective. Drug Resist Updat. 2011 Apr;14(2):107-17.

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