Supratherapeutic Posaconazole Concentration in a Pediatric Transplant Patient With Confirmed Rhizopus Infection

There are a limited number of studies that guide dosing of posaconazole delayed-release (DR) tablets for the pediatric population. Current FDA-approved doses are only recommended for patients 13 years and older. For younger patients, providers are faced with the challenge of recommending posaconazole doses extrapolated from adult studies or choosing an alternative agent. We report on a case of a 10-year-old patient who experienced a supratherapeutic trough serum concentration and transaminitis after receiving the extrapolated adult dosage of posaconazole DR tablets (300 mg twice daily for the first day, followed by 300 mg daily) for 7 days. In the end, the patient required a smaller dose of 200 mg daily to achieve the desired trough target concentration for the treatment of a Rhizopus neck infection. Our findings highlight the need for additional studies to determine the optimal dosing of posaconazole DR tablets for children.

Should the Vancomycin Minimal Inhibitory Concentration be used as an Infant Critical Care Regular Criteria?

Background: Vancomycin is the first-line antibiotic used for the treatment of staphylococcal infections. Because of its narrow therapeutic window and the pharmacokinetics variability, vancomycin trough serum concentration should be monitored. However, due to the increased cases of staphylococcus’ commensal species infections and the case of vancomycin resistance, the minimal inhibitory concentration should be considered on antimicrobial therapy. Objective: This article aimed to show the importance of the minimal inhibitory concentration to infants on vancomycin therapy as regular criteria. Materials and Methods: Three infants in the use of vancomycin, hospitalized in the same maternity hospital, and that had at least one blood culture performed during the intensive-care-unit hospitalization were included in the study. Vancomycin serum concentrations were determined by particleenhanced- turbidimetric inhibition-immunoassay. The vancomycin minimal inhibitory concentration data were interpreted by following the Clinical and Laboratory Standards Institute (CLSI) and the European Committee on Antimicrobial Susceptibility Testing (EUCAST). The trough serum concentration range of 10 to 20 mg.L-1 was considered therapeutic. Results: All three patients had at least one infection by S. epidermidis, being one patient exhibit vancomycin- resistant S. epidermidis infection. All patients had stoppages in the vancomycin treatment, and the minimal inhibitory concentration was performed for only one patient. Conclusion: The data obtained from these patients also showed the need to perform therapeutic monitoring by using minimal inhibitory concentration values, because, although the serum concentrations were within the reference range, they are insufficient to guarantee patient therapeutic success.

Vancomycin AUC/MIC and Corresponding Troughs in a Pediatric Population

OBJECTIVES Adult guidelines suggest an area under the curve/minimum inhibitory concentration (AUC/MIC) > 400 corresponds to a vancomycin trough serum concentration of 15 to 20 mg/L for methicillin-resistant Staphylococcus aureus infections, but obtaining these troughs in children are difficult. The primary objective of this study was to assess the likelihood that 15 mg/kg of vancomycin every 6 hours in a child achieves an AUC/MIC > 400. METHODS This retrospective chart review included pediatric patients >2 months to <18 years with a positive S aureus blood culture and documented MIC who received at least two doses of vancomycin with corresponding trough. Patients were divided into two groups: group 1 initially receiving ≥15 mg/kg every 6 hours, and group 2 initially receiving any other dosing ranges or intervals. AUCs were calculated four times using three pharmacokinetic methods. RESULTS A total of 36 patients with 99 vancomycin trough serum concentrations were assessed. Baseline characteristics were similar between groups. For troughs in group 1 (n = 55), the probability of achieving an AUC/MIC > 400 ranged from 16.4% to 90.9% with a median trough concentration of 11.4 mg/L, while in group 2 (n = 44) the probability of achieving AUC/MIC > 400 ranged from 15.9% to 54.5% with mean trough concentration of 9.2 mg/L. The AUC/MICs were not similar between the different pharmacokinetic methods used; however, a trapezoidal equation (Method A) yielded the highest correlation coefficient (r2 = 0.59). When dosing every 6 hours, an AUC/MIC of 400 correlated to a trough serum concentration of 11 mg/L. CONCLUSIONS The probability of achieving an AUC/MIC > 400 using only a trough serum concentration and an MIC with patients receiving 15 mg/kg every 6 hours is variable based on the method used to calculate the AUC. An AUC/MIC of 400 in children correlated to a trough concentration of 11 mg/L using a trapezoidal Method to calculate AUC.

Vancomycin Dosing in Healthy-Weight, Overweight, and Obese Pediatric Patients

OBJECTIVES: With an increase in vancomycin resistance and the prevalence of obesity in children, alterations of vancomycin dosing regimens may be necessary to achieve target serum concentrations. The primary objective of this study was to describe initial vancomycin dosing with resulting serum concentrations in healthy-weight and overweight/obese children. Secondary objectives include comparing vancomycin dosing regimens of healthy-weight and overweight/obese patients that produced target trough serum concentrations and evaluating the likelihood of attaining target concentrations by patient characteristics. METHODS: This retrospective review evaluated healthy-weight and overweight/obese patients, aged 2 to 18 years, who had vancomycin trough serum concentrations obtained between 2005 and 2010. Vancomycin dosing, initial trough serum concentrations, pharmacokinetic parameters, and patient demographics were collected for analysis. Target trough serum concentrations were defined as 10 to 20 mg/L. RESULTS: The study included 98 patients (48 healthy weight, 50 overweight/obese) of which only 14 patients (14.2%, 6 healthy weight, 8 obese) reached a target trough serum concentration with empiric dosing. No difference was found between the mean daily dosing of vancomycin that produced target trough serum concentrations in healthy-weight or overweight/obese patients (53.63 mg/kg/day vs 51.6 mg/kg/day, respectively). Demographic or clinical characteristics were not found to be associated with the likelihood of target trough serum concentration attainment. CONCLUSIONS: Vancomycin dosing in healthy-weight and overweight/obese pediatric patients did not reach target trough serum concentrations most of the time. In obtaining initial target serum concentrations, no dosing difference was identified for overweight/obese patients compared with healthy-weight patients. Alternate dosing strategies, therapeutic monitoring, and clinical outcomes should continue to be evaluated in this population.

Optimizing Vancomycin Dosing through Pharmacodynamic Assessment Targeting Area under the Concentration-Time Curve/Minimum Inhibitory Concentration

Because of its activity against multidrug resistant gram-positive organisms, vancomycin is one of the antimicrobials most utilized in health care systems worldwide. Despite its widespread use, application of the pharmacodynamic principles governing vancomycin efficacy are not frequently considered in contemporary clinical practice. Although the vancomycin trough serum concentration has been used historically to assess the adequacy of a prescribed dose, data validating that this practice leads to improved patient outcomes do not exist. Alternatively, both in vitro and clinical outcomes data demonstrate improved results when an area under the concentration-time curve/minimum inhibitory concentration (AUC/MIC) of 400 mcg•h/mL or greater is achieved. This article describes the process through which individualized vancomycin dosing regimens targeting an AUC/MIC of 400 mcg•h/mL or greater, rather than trough serum concentration, at the beside can be derived. The equations, methodology, thought processes, benefits, potential pitfalls, and practical applicability of this method are specifically examined. Obtaining the actual MIC value—not an interpretation—from the microbiology laboratory and/or the MIC distribution for Staphylococcus aureus within one's own institution is essential for implementation of this method. Although vancomycin dosing recommendations suggested in contemporary practice guidelines are likely adequate for most patients, using the methods described here may lead to improved clinical outcomes for nonstandard conditions in patients who are critically ill and would benefit from an individualized dosing approach.