Therapeutic drug monitoring (TDM), which involves measurement of drug or active metabolite levels and anti-drug antibodies, is a promising strategy that can be used to optimize inflammatory bowel disease therapeutics. It is based on the premise that there is a relationship between drug exposure and outcomes, and that considerable inter-individual variability exists in how patients metabolize the drug (pharmacokinetics) and the magnitude and duration of response to therapy (pharmacodynamics). Therefore, the American Gastroenterological Association has prioritized clinical guidelines on the role of TDM in the management of inflammatory bowel disease. To inform these clinical guidelines, this technical review was developed in accordance with the GRADE (Grading of Recommendations Assessment, Development, and Evaluation) framework for interventional and prognostic studies, and focused on the application of TDM for biologic therapy, specifically anti-tumor necrosis factor-α agents, and for thiopurines. Focused questions address the benefits and risks of a strategy of reactive TDM (in patients with active inflammatory bowel disease) to guide treatment changes compared with empiric treatment changes, and the benefits and risks of a strategy of routine proactive TDM (during routine clinical care in patients with quiescent disease) compared with no routine TDM. Additionally, the review addresses the benefits and risks of routine measurement of thiopurine methyltransferase enzyme activity or genotype before starting thiopurine therapy compared with empiric weight-based dosing and explores the performance of different trough drug concentrations for anti-tumor necrosis factor agents and thiopurines to inform clinical decision making when applying TDM in a reactive setting. Due to a paucity of data, this review does not address the role of TDM for more recently approved biologic agents, such as vedolizumab or ustekinumab.

Data from the infliximab safety database suggest that infliximab exposure during pregnancy results in outcomes that do not differ from those in the U.S. population of pregnant women and pregnant women with CD not exposed to infliximab. No increased risk of adverse outcome was detected, however, follow-up of larger numbers of pregnant women exposed to infliximab will be necessary to definitively exclude any fetal risk.

Background: The CD40/CD40L system, a key regulator and amplifier of immune reactivity, is activated in inflammatory bowel disease (IBD) mucosa. Aims: To determine whether plasma levels of sCD40L are elevated in Crohn's disease (CD) and ulcerative colitis (UC) patients compared with normal controls, to investigate the cellular source of sCD40L, and to explore CD40L induction mechanisms. Patients: CD, UC, and normal control subjects were studied. Methods: The concentration of sCD40L in plasma and supernatants of freshly isolated platelets and autologous peripheral blood T cells (PBT) was measured by ELISA. Surface CD40L expression level was measured by flow cytometry in resting and thrombin activated platelets, and unstimulated and CD3/CD28 stimulated PBT before and after coculture with human intestinal microvascular endothelial cells (HIMEC). Results: Compared with normal controls, plasma sCD40L levels were significantly higher in both CD and UC patients and proportional to the extent of mucosal inflammation. Platelets from IBD patients displayed a significantly higher surface CD40L expression than those from control subjects, and released greater amounts of sCD40L than autologous PBT. Contact with IL-1b activated HIMEC induced significant upregulation of CD40L surface expression and release by platelets. Conclusions: Elevated levels of sCD40L in the circulation of IBD patients reflect enhanced surface expression and release of CD40L by platelets. This phenomenon translates to an increased platelet activation state apparently induced by passage through an inflamed mucosal microvascular bed, a conclusion supported by the positive correlation of plasma sCD40L levels with the extent of anatomical involvement by IBD. These results suggest that platelet-endothelial interactions critically contribute to activation of the CD40 pathway in IBD.

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