Relationship Status between Vancomycin Loading Dose and Treatment Failure in Patients with MRSA Bacteremia: It’s Complicated

INTRODUCTION: A one-time vancomycin loading dose of 25–30 mg/kg is recommended in the current iteration of the vancomycin consensus guidelines in order to more rapidly achieve target serum concentrations and hasten clinical improvement. However, there are few clinical data to support this practice, and the extents of its benefits are largely unknown. METHODS: A multicenter, retrospective, cohort study was performed to assess the impact of a vancomycin loading dose (≥ 20 mg/kg) on clinical outcomes and rates of nephrotoxicity in patients with methicillin-resistant Staphylococcus aureus (MRSA) bacteremia. The study matched patients in a 1:1 fashion based on age, Pitt bacteremia score, and bacteremia source. The primary outcome was composite treatment failure (30-day mortality, bacteremia duration ≥ 7 days after vancomycin initiation, persistent signs and symptoms of infection ≥ 7 days after vancomycin initiation, or switch to an alternative antimicrobial agent). Secondary outcomes included duration of bacteremia, length of stay post-bacteremia onset, and nephrotoxicity. RESULTS: A total of 316 patients with MRSA bacteremia were included. Median first doses in the loading dose and non-loading dose groups were 23.0 mg/kg and 14.3 mg/kg, respectively (P < 0.001). No difference was found in composite failure rates between the non-loading dose and loading dose groups (40.5% vs. 36.7%; P = 0.488) or in the incidence of nephrotoxicity (12.7% vs. 16.5%; P = 0.347). While multivariable regression modeling showed receipt of a vancomycin loading dose on a mg/kg basis was not significantly associated with composite failure [aOR 0.612, 95% CI (0.368–1.019)]; post hoc analyses demonstrated that initial doses ≥ 1750 mg were independently protective against failure [aOR 0.506, 95% CI (0.284–0.902)] without increasing the risk for nephrotoxicity [aOR 0.909, 95% CI (0.432–1.911)]. CONCLUSION: These findings suggest that initial vancomycin doses above a certain threshold may decrease clinical failures without increasing toxicity and that weight-based dosing might not be the optimal strategy. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1007/s40121-019-00268-3) contains supplementary material, which is available to authorized users.