FAILURE OF SUPPRESSIVE ANTIBIOTIC THERAPY IN PROSTHETIC JOINT INFECTION: A CHART REVIEW

Literature on suppressive antibiotic therapy (SAT) in prosthetic joint infection (PJI) is sparse and provides little guidance during the complex treatment these patients require. We aimed to identify patient characteristics and outcomes for PJI cases treated with SAT in a Canadian centre. Using a two-step selection process, we identified all patients included in our database who underwent revision arthroplasty (hip or knee) for infection between March, 2003 and April, 2023 and received antibiotics longer than 90 consecutive days before and/or after the revision. In step one, we identified all revisions for infection from our database and then, in step two, performed a chart review to identify antibiotic drug use. We identified the index revision as the first revision while on SAT or the revision just before starting SAT. For the patients identified in this selection process, we performed an in-depth chart review from 90 days before the index revision until the subsequent revision (or the end of the study period). We extracted each prescription for antibiotics and each reported test result for c-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) as well as all reported culture and sensitivity results, in addition to patient and characteristics during the index revision. We defined four different outcomes, revision (any subsequent revision on the same joint), end of SAT (>30 days without a new prescription for antibiotics), death (for any reason), or end of the study period (April 30, 2023). We used standard time-to-event (survival) analysis, where patients entered the cohort on their index revision date and exited the cohort at the earliest outcome date. We used Cox proportional hazard models to estimate the hazard ratio (HR) of the association between index characteristics revision, while censoring patients for other outcomes. Of the 87 patients identified (30 hips and 57 knees), 60% were male, median age was 65, and median BMI was 32.2 kg/m2. The index CRP, measured up to 60 days prior to surgery, ranged widely (interquartile range 6-102 mg/L, unknown for one-third of patients) as did the ESR (interquartile range 20-65 mm/h, unknown for nearly half the patients). S. aureus (15 MSSA+3 MRSA patients) and S. epidermidis (12 patients) were the most commonly identified pathogens, but one-third of patients were culture-negative. Across all patients, 18 had a revision, 61 ended their SAT, 1 died, and 7 remained revision-free on SAT until the end of the study period. Having an above-median CRP (≥30 mg/L among our patients with infection) was associated with a significantly increased risk of revision, crude HR 4.3 (95% confidence interval [95% CI] 1.2-15.8) and adjusted (for age, sex, BMI, and index ESR) HR 4.4 (95% CI 1.1-17.0). Above-median ESR (≥38 mm/h), on the other hand, was not associated with revision risk, crude HR 1.2 (95% CI 0.4-3.4) and adjusted HR 0.8 (95% CI 0.2-2.8). Higher CRP levels were associated with a higher risk of revision for patients on SAT for PJI, whereas ESR levels were not associated with revision risk.