February 18, 2019
1 min read

Measuring vancomycin use by days of therapy underestimates exposure

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Shutaro Murakami, BScPharm
Shutaro Murakami

Using days of therapy, or DOT, to estimate vancomycin use may underestimate exposure to the antibiotic by around 10% compared with therapeutic drug-monitoring, or TDM, according to findings published in Infection Control & Hospital Epidemiology.

“The difference in vancomycin exposure between [the] two measurements was statistically significant,” Shutaro Murakami, BScPharm, from the department of pharmacy at Tokyo Metropolitan Tama Medical Center, told Infectious Disease News. “Because calculating antimicrobial exposure with intermittent dosing of vancomycin is challenging, the finding in our study suggests that we may be able to more accurately estimate actual vancomycin exposure using TDM-based exposure days.”

Murakami and colleagues conducted a retrospective observational study using data collected at the Tokyo Metropolitan Tama Medical Center between April 2012 and March 2018. They determined the mean monthly vancomycin use to be 343.5 DOT (standard deviation [SD] = 87.3) compared with 383.8 TDM-based exposure days (SD = 88.9). The difference of exposure between DOT and TDM-based exposure days was –40.3 days (SD = 16.9), and the relative difference was –10.9% (SD = 4.9%), they reported.

Murakami and colleagues found that DOT was 27.4 days among patients with creatine clearance (CrCl) less than 30 mL [ (SD = 17.5), whereas TDM-based exposure days was 36.7 (SD = 20.5) — an absolute difference of –9.3 days (SD = 7.3) and relative difference of –25.9% (SD = 18.9%). Among patients on dialysis, DOT was 27.7 (SD = 15.5) and there were 50.7 (SD = 26.9) TDM-based exposure days — an absolute difference of –23 days (SD = 14.1) and relative difference of –44.8% (SD = 12.4%).

Murakami and colleagues suggested that TDM-based exposure days are a better method of measuring exposure duration in patients with impaired renal function.

“[A] method of estimating vancomycin exposure using TDM-based exposure days may be more suitable for patients with labile renal function (eg, elderly population) or ICUs where there can be a significant fluctuation in DOT measurement due to the high proportion of patients with impaired or labile renal function,” Murakami said. “Further studies will be needed to clarify if the more accurate calculation of vancomycin exposure has an impact on specific clinical outcomes.” – by Marley Ghizzone

Disclosures: The authors report no relevant financial disclosures.