Inappropriate Antimicrobial Dosing in Regard to Renal Function in a Tertiary Hospital in Greece—A Single-Center Point Prevalence Study

Background and Objectives: Appropriate antimicrobial dosing according to kidney function is essential to ensure therapeutic efficacy while minimizing toxicity and antimicrobial resistance. Despite established dosing guidelines and electronic prescribing systems, errors in renal dose adjustment of antimicrobials, particularly in the setting of acute kidney injury, remain common among hospitalized patients. Materials and Methods: A point-prevalence study was conducted on 31 October 2024 at a tertiary-care hospital in Greece to evaluate the appropriateness of antimicrobial dosing in relation to renal function. Patient characteristics, renal parameters, and antimicrobial prescriptions were extracted from electronic medical records. Glomerular filtration rate (GFR) was estimated using the MDRD formula. Comparative analyses were performed between correctly and incorrectly dosed cases, and between overdosing and underdosing episodes. Results: A total of 235 hospitalized patients were evaluated (mean age 64.8 ± 18.6 years; 43.4% female). Overall, 15.7% (37/235) received at least one antimicrobial dose inappropriate for their renal function. Among 37 patients where dosing errors were identified, overdosing was noted in 23 (62.2%), underdosing in 16 (43.2%), adding up to 39 prescriptions, while in 2 patients (5.4%), both mistakes were noted in different prescribed antimicrobials. Drug-specific error rates varied considerably: ceftazidime and cefuroxime showed the highest rates of inappropriate dosing (40% each), followed by colistin (33.3%) and acyclovir (33.3%). Piperacillin/tazobactam, the most frequently prescribed agent (n = 50), had a 14% error rate, mainly due to underdosing (10%). Patients with dosing errors were significantly older (71.5 vs. 64.1 years, p = 0.0220) and had worse renal function, including higher serum creatinine (1.68 vs. 1.19 mg/dL, p = 0.0174), lower GFR (58.5 vs. 75.9 mL/min/1.73 m2, p = 0.0009), and more frequent dialysis (13.5% vs. 4.3%, p = 0.0422). They also received a higher median number of antimicrobials (2 vs. 1, p = 0.0185). Conclusions: Inappropriate antimicrobial dosing based on kidney function remains common in hospitalized patients, particularly among older individuals and those with impaired renal function or polypharmacy. Targeted antimicrobial stewardship strategies focusing on renal dose adjustment and agents that are more frequently dosed inappropriately, such as colistin, acyclovir, cefuroxime, and ceftazidime, as well as agents that are frequently prescribed despite a relatively lower rate of inappropriate dose, such as piperacillin/tazobactam, are needed to enhance prescribing safety and optimize therapeutic outcomes.