Therapeutic drug monitoring in inflammatory bowel disease patients on vedolizumab

Objective: We aimed to investigate whether vedolizumab (VDZ) levels were associated with inflammatory markers or clinical or endoscopic scoring in inflammatory bowel disease (IBD). Methods: Besides demographic data, clinical scoring, endoscopic data, and laboratory markers of IBD patients treated with VDZ from 2015 to 2020 who had trough levels drawn on maintenance therapy were collected at baseline and at follow-up (after at least 8 weeks on VDZ therapy or after change in dose frequency). Low drug levels were defined as VDZ trough <20 μg/mL. Results: We identified 89 patients with a mean age of 42.9 years. Of the 90 total trough levels drawn, 61.1% were low. Among patients on every 8 week (Q8 week) VDZ dosing, 81.5% had low troughs. After increasing dosing frequency to Q4 weeks, all patients showed improvement in VDZ levels, but 30.6% remained <20 μg/mL. Higher VDZ levels on Q8 week dosing were associated with higher albumin levels (P = 0.01). While higher VDZ levels on Q4 week dosing were associated with higher albumin (P = 0.02), lower erythrocyte sedimentation rate (P = 0.04) and higher likelihood of having mild disease or endoscopic remission (P = 0.01). No significant association was found between VDZ levels and clinical scoring, body mass index, hemoglobin, vitamin D or platelet levels on either Q8 or Q4 week dosing. Conclusions: Higher VDZ troughs were associated with higher albumin, mild endoscopic disease or endoscopic remission. Patients who continue to have low VDZ troughs despite Q4 week dosing may require a change in therapy.