1576. Delaying the Start of Maintenance Vancomycin After a Loading Dose to Avoid a High 0–24h AUC

BACKGROUND: Vancomycin dosing guidelines recommend loading doses (LDs) (25–30 mg/kg TBW), and a maintenance regimen, usually started after a time period equal to the dosing interval. Studies of vancomycin exposure and nephrotoxicity conclude that a 0 to 24-hour area under the serum concentration–time curve (0–24AUC) > 677 mg-hour/L results in a 3- to 4-fold increased risk of nephrotoxicity (Zasowski EJ, Antimicrob Agents Chemother 2018). For vancomycin LDs we compare the calculated LD and the maintenance dose, and delay initiation of the maintenance regimen when the LD exceeds the daily maintenance dose by > 50%. This study assessed the pharmacokinetic outcomes from this technique. METHODS: We retrospectively reviewed 68 consecutive adult patients receiving therapeutic doses of vancomycin. Patient age, sex, height, weight, serum creatinine, and indication were used to calculate the daily dose/intervals for a steady-state 24-hr AUC of 400 or 600 mg-hour/L. The total 0–24AUC was calculated by adding the 0–24 AUC from a 25 mg/kg LD (max: 3 gm) to the 0–24AUC(s) for maintenance dose(s) within the first 24 hours. We compared the total 0-24AUC when the first maintenance dose was timed for the next dosing interval (“scheduled”) to that when the maintenance dose was delayed according to our protocol (“delayed”). We tested the proportion of patients who would be exposed to a vancomycin 0-24AUC > 677 mg-hour/L. RESULTS: 16/68 patients were diagnosed with SSTI (goal 24 hr AUC: 400 mg-hour/L) and 52/68 with sepsis, bacteremia/endocarditis, or pneumonia (24 hr AUC: 600 mg-hour/L). Median daily maintenance dose was 1750 mg (range: 875–4,000 mg). For patients with a goal AUC of 400, the 0-24AUC was > 677 mg-hour/L in one patient using the “scheduled” process and in none of the patients using the “delayed” protocol. However, for patients with a goal AUC of 600, the 0-24AUC was > 677 mg-hour/L in 22/52 patients via the “scheduled” process vs. 4/52 patients via the “delayed” protocol. CONCLUSION: For patients with severe gram-positive bacterial infections requiring aggressive dosing of vancomycin, delaying the start of maintenance dosing following a large LD is an effective way to ensure attainment of goal therapeutic AUC within the first 24 hr without placing the patient at increased risk for nephrotoxicity. DISCLOSURES: All authors: No reported disclosures.