Category Archives: Infectious Disease

New Colistin (colistimethate sodium) Calculator

Pseudomonas aeruginosa nutrient agar

Colistin (in the form of colistimethate sodium, or CMS, in the United States) is an older, last-line agent for multidrug-resistant gram-negative infections.  Because of colistin’s complex pharmacokinetics and for historical reasons, there is a paucity of data regarding its dosing in patients with severe gram negative infections, particularly for those with concurrent renal dysfunction.

In one of the largest pharmacokinetic analyses of colistin to date, Garonzik et al. published a detailed analysis of CMS dosing in critically ill patients.  This analysis included dosing recommendations for patients with normal renal function, acutely changing renal function, intermittent hemodialysis (IHD), and continuous renal replacement therapy (CRRT).

ClinCalc is excited to announce our new colistin dosing calculator, which is based on the Garonzik pharmacokinetic recommendations.  This calculator was developed in coordination with Julie Ann Justo, PharmD, MS, BCPS, AAHIVP — an Assistant Professor at the South Carolina College of Pharmacy who specializes in infectious diseases and HIV pharmacotherapy. Continue reading

Eight Quick Tips on Inferring Antibiotic Susceptibility Results

Photo courtesy Nathan Reading (Staphylococcus aureus - Inducible Macrolide Resistance)

Antibiotic susceptibility testing is commonly used to select appropriate antimicrobial therapy or deescalate to a narrower spectrum agent.  Because not every antibiotic is tested, clinicians must infer certain types of antibiotic susceptibility based on bacterial patterns of resistance and sensitivities of other antibiotics.

The following are 8 quick tips regarding inferred antibiotic susceptibility, which are based on the EUCAST clinical breakpoints document (see references). Continue reading

Vancomycin AUC:MIC versus T>MIC

There is a significant amount of controversy regarding the most appropriate therapeutic goal for vancomycin therapy. The difference of opinion stems from the pharmacodynamic activity of vancomycin.


  • MIC (minimum inhibitory concentration) – The minimum concentration of antibiotic to inhibit the growth of an organism.
  • AUC (area under the curve) – The total exposure of an antibiotic to an organism Continue reading

The Evidence behind Continuous-Infusion Vancomycin Therapy

Vancomycin is typically given as an intermittent infusion adjusted for body weight and renal function.  Some clinicians believe that a continuous infusion of vancomycin may simplify therapy and make serum vancomycin levels more consistent.

Goal Vancomycin Level (Plateau)

Because continuous infusion vancomycin is a rare clinical occurrence, there is a lack of data regarding the optimal “plateau” level (serum drug level during continuous infusion therapy).  Current evidence suggests that the vancomycin AUC:MIC ratio is the most important pharmacodynamic parameter associated with treatment success.1  Given that current guidelines recommend an AUC:MIC ratio of at least 400, a plateau of 20-25 mcg/mL (20 mcg/mL * 24 hrs) would provide an AUC:MIC ratio > 400 for isolates with an MIC of 1-1.5 mcg/mL. Continue reading

How to Interpret a Voriconazole Drug Level

Voriconazole (VFEND®) is a second-generation azole antifungal that inhibits 14-α-demethylase, causing reduced production of ergosterol, a critical component of the fungal the cell wall.  Voriconazole has a broader spectrum of activity than fluconazole and is often used for the treatment of invasive aspergillosis.  Voriconazole serum concentrations are difficult to predict because of its saturable metabolism, non-linear pharmacokinetics, and poor correlation to weight-based dosing.1 Continue reading