Therapeutic monitoring of infliximab is limited by the time lag between drug-level measurement and dose adjustment, along with the cost of dose escalation. Strategies for dose reduction in stable patients on maintenance infliximab at supratherapeutic levels are uncertain. This study determined the feasibility of a pharmacist-driven strategy for immediate dose adjustment using a sliding scale at the point of care in stable patients with inflammatory bowel disease on maintenance therapy.
Adult patients with stable disease undergoing maintenance therapy with infliximab infusions, 5 mg/kg every 8 weeks, were prospectively studied. Trough drug levels were assessed by a rapid assay (and later by ELISA) at all infusions for up to 12 months with immediate but quantitatively small dose adjustment according to a sliding scale targeting a therapeutic range of 3-7 µg/mL. Disease activity was assessed both clinically and biochemically.
The rapid assay and ELISA detected similar infliximab levels, and the strategy added approximately 30 min to the duration of infusion events. Only 20% of 48 patients (77% with Crohn's disease) had baseline trough infliximab concentrations within the therapeutic range. This value increased threefold after 24 and 48 weeks of interventions. One in two patients had baseline supratherapeutic levels and most were brought into the therapeutic range without discernible impact on disease activity by one dose adjustment, but two or three adjustments were generally needed for 29% of patients with sub-therapeutic levels. Overall, drug costs were reduced by 4%.
Immediate dose adjustment following infliximab rapid assay performed by a pharmacist using a sliding scale is a feasible strategy. Supratherapeutic infliximab levels can be safely and quickly brought into the therapeutic range using small dose adjustments without impacting disease activity, offsetting (at least partly) costs associated with dose escalation.