Higher body weight and current smoking are associated with lower concentrations of perioperative antibiotic prophylaxis in the synovial fluid of the shoulder joint.

BACKGROUND: Surgical site infections are a clinically relevant complication in orthopedic surgery, and administration of perioperative antibiotic prophylaxis has been shown to reduce infection rates. This study aimed to identify influencing factors on the concentration of unbound cefazolin in shoulder synovial fluid, following the perioperative antibiotic prophylaxis administration of 2 g of cefazolin during shoulder surgery.

METHODS: Patients who underwent arthroscopic or open shoulder surgery within 5 months were prospectively included. The exclusion criteria were patient age under 18 years, shoulder joint infection, beta-lactam allergy, and creatinine clearance below 30 ml/min. All patients received 2 g of cefazolin pre-operatively via intravenous short infusion. The infusion duration, sampling time, patient age, body weight, body mass index, American Society of Anesthesiologists score, smoking status and diabetes status were documented. Unbound cefazolin concentrations in the synovial fluid were determined using ultrafiltration and ultra-high-performance liquid chromatography coupled to tandem mass spectrometry. Multiple linear regression analysis with backward elimination (significance level P < .05) was used to analyze influencing factors on unbound cefazolin concentration.

RESULT: A total of 62 patients (35 men (56.5%), age 57.1 ± 15.4 years, body weight 88.2 ± 18.5 kg) were included in the final evaluation. The unbound cefazolin concentration was 20.2 ± 8.6 μg/mL. Increasing body weight and current smoking independently negatively influenced the unbound cefazolin concentration (B = -.217, P = < .001 and B = -6.631, P = .002, respectively). No significant correlation was found with age, sex, body mass index, American Society of Anesthesiologists score, diabetic status, creatinine clearance and the time interval between perioperative antibiotic prophylaxis administration and sample collection. Sufficient drug concentrations were detected in all cases against Cutibacterium acnes (2 μg/mL). The fourfold epidemiologic cut-off value for Staphylococcus aureus (8 μg/mL) was achieved in 58 patients (93.5%). In 55 patients (88.7%), the unbound drug concentrations were below 4 times the epidemiologic cut-off value for coagulase-negative staphylococci (32 μg/mL).

CONCLUSIONS: Higher body weight and current smoking are associated with lower unbound cefazolin concentrations in shoulder synovial fluid. Patient-specific adjustment of cefazolin dosing may be considered to optimize perioperative antibiotic prophylaxis.