Occurrence and predictors of laboratory abnormalities during outpatient parenteral antimicrobial therapy – A multicenter cohort study to inform laboratory test monitoring

Objectives: Evidence on the optimal frequency of laboratory testing during outpatient parenteral antimicrobial therapy (OPAT) is lacking. Therefore, we investigated how often and when laboratory abnormalities occur during OPAT and which factors are associated with these abnormalities. Methods: We performed a multicenter cohort study in four Dutch hospitals among adult patients receiving OPAT and collected routinely obtained laboratory test results. Incidence and incidence rates were calculated for various laboratory abnormalities. Survival analysis was performed to visualize the time to the first occurrence of laboratory abnormalities and Poisson regression analysis to compare the number of abnormalities in the first and second 30 OPAT days among patients receiving OPAT for =60 days. Predictors were identified using a multivariable Cox proportional hazard regression model. Results: 45.1% of 1152 included patients developed laboratory abnormalities, but only 2% led to OPAT discontinuation. Hepatotoxicity was most common (33.9 events/1000 OPAT days), with a time-dependent decrease in the occurrence of the first hepatotoxic event, while hypokalemia was rare (1.7 events/1000 OPAT days). In the subgroup of patients receiving =60 days of OPAT, nephrotoxicity was more common in days 31–60. We observed partly toxicity-specific associations between antibiotic type, concomitant medication, baseline laboratory values, patient characteristics, and the occurrence of laboratory abnormalities. Conclusions: While laboratory abnormalities are frequently observed during OPAT, they rarely lead to discontinuation of OPAT. Specific patient, treatment and laboratory characteristics were associated with the occurrence of laboratory abnormalities. Based on our results, we recommend a more personalized laboratory monitoring policy with less blood sampling.