Target Serum Concentration of Vancomycin May Be Reached Earlier with a Loading Dose

Introduction

Vancomycin remains a first-line antibiotic for invasive methicillin-resistant Staphylococcus aureus (MRSA) infections. However, treatment failures are not uncommon, even when pathogens are classified as vancomycin-susceptible. Suboptimal trough serum concentrations of vancomycin are a significant contributor to these failures. Clinicians often face pressure to switch antibiotics prematurely due to persistent symptoms, such as fever, within the first day of treatment. Traditional dosing regimens require measuring serum concentrations before the fifth dose, typically on the third day of therapy, which delays confirmation of therapeutic efficacy. A loading dose strategy has been proposed to accelerate the attainment of target trough concentrations, potentially improving clinical outcomes without increasing toxicity risks. This study evaluated whether a loading dose of vancomycin could achieve therapeutic serum levels earlier and assessed its safety profile in critically ill patients.

Methods

Study Design and Population

This retrospective cohort study was conducted in the intensive care unit (ICU) of Ruijin Hospital North, Shanghai Jiao Tong University School of Medicine, between June 2018 and June 2020. Patients aged >18 years with suspected or confirmed gram-positive cocci infections treated with vancomycin were included. Exclusion criteria included renal replacement therapy, vancomycin treatment duration <3 days, incomplete data, prior vancomycin use within 3 days of ICU admission, pregnancy, or a switch from bolus to continuous infusion before the fifth dose.

Group Allocation and Dosing

Patients were divided into two groups:

1. Loading Group: Received an initial vancomycin dose 1.5 times the maintenance dose, adjusted for creatinine clearance (CrCl).
2. Control Group: Received standard maintenance dosing from the first dose.

Maintenance doses were calculated using the formula:
[ text{Maintenance Dose} = text{CCr} times 15 , text{mg/kg/day} ]
where CrCl was estimated using the Cockcroft-Gault equation.

Data Collection

Baseline demographics, clinical scores (APACHE II, SOFA), infection sources, pathogen data, vancomycin doses, serum concentrations, and outcomes were collected. Serum vancomycin levels were measured before the second and fifth doses. Renal function was monitored via serum creatinine (Cr), blood urea nitrogen (BUN), and cystatin C for 7 days.

Statistical Analysis

Continuous variables were reported as mean ± standard deviation or median (interquartile range), and categorical variables as frequencies. The Student’s t-test, Wilcoxon rank-sum test, and chi-squared test were used for comparisons. A P-value <0.05 was considered statistically significant.

Results

Patient Characteristics

Fifty-five patients were included: 29 in the loading group and 26 in the control group. The groups had comparable baseline characteristics, including age, sex, body mass index, APACHE II (12 vs. 15, P=0.083), and SOFA scores (5 vs. 6, P=0.238). Common infection sources were pulmonary (55.2% vs. 61.5%), bloodstream (24.1% vs. 23.1%), and skin/soft tissue (13.8% vs. 11.5%). Pathogens isolated included Staphylococcus aureus, Staphylococcus epidermidis, and Enterococcus species. Minimum inhibitory concentrations (MICs) for vancomycin were 0.5 mg/L (24%), 1 mg/L (36%), and 2 mg/L (40%).

Vancomycin Concentrations

The loading group received a significantly higher first dose (median 22.2 mg/kg vs. 14.2 mg/kg, P<0.001). Before the second dose, serum vancomycin concentrations were nearly double in the loading group (10.3 ± 6.1 mg/L vs. 5.7 ± 4.4 mg/L, P=0.002). By the fifth dose, concentrations converged (12.4 ± 7.3 mg/L vs. 10.3 ± 6.3 mg/L, P=0.251), indicating that standard dosing eventually achieved similar levels but required more time.

Clinical Outcomes

The 28-day mortality was significantly lower in the loading group (6.7% vs. 34.6%, P=0.026). No differences in ICU stay duration or total vancomycin exposure were observed.

Safety and Renal Function

Baseline Cr levels were similar between groups (85.0 ± 52.7 vs. 68.5 ± 22.0 µmol/L, P=0.146). Over 7 days, Cr, BUN, and cystatin C remained stable in both groups (P>0.05 for all comparisons). Two patients in the loading group and one in the control group had pre-existing renal dysfunction, but none experienced acute kidney injury attributable to vancomycin.

Discussion

Accelerated Target Attainment

The study demonstrated that a loading dose of vancomycin achieves therapeutic serum concentrations earlier than standard dosing. This aligns with prior studies recommending loading doses of 25–30 mg/kg or fixed 2 g doses. Early target attainment is critical in critically ill patients, where delays in effective therapy correlate with higher mortality.

Mortality Benefit

The significant reduction in 28-day mortality (6.7% vs. 34.6%) underscores the clinical relevance of rapid vancomycin optimization. Early therapeutic concentrations may enhance bacterial clearance, reduce inflammatory responses, and prevent sepsis progression.

Safety Profile

No increased nephrotoxicity was observed, contradicting concerns that higher initial doses might harm renal function. This finding supports the safety of loading doses, even in patients with baseline renal impairment, provided CrCl-guided adjustments are used.

Limitations

The retrospective design introduces potential confounding, such as unmeasured variables influencing mortality. The small sample size limits generalizability, and long-term renal outcomes were not assessed. Additionally, pathogens with higher MICs (2 mg/L) represented 40% of isolates, which may necessitate higher trough targets (>15 mg/L) per recent guidelines.

Clinical Implications

Loading doses tailored to CrCl can expedite therapeutic vancomycin levels, potentially reducing mortality in gram-positive infections. Routine therapeutic drug monitoring before the second dose could further optimize dosing in critically ill patients.

Conclusion

A loading dose of vancomycin accelerates the attainment of target serum concentrations without increasing renal toxicity. This strategy may improve survival in critically ill patients with gram-positive infections. Larger prospective studies are needed to validate these findings and refine dosing protocols.

doi.org/10.1097/CM9.0000000000001905

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