Therapeutic drug monitoring in inflammatory bowel disease: The dawn of reactive monitoring

Table 1 Association between various thresholds for serum drug concentrations and clinical outcomes

Drug	Serum drug level	Clinical outcome
Infliximab (IFX)
IFX	< 2 μg/mL for CD/UC at week 14	Increased incidence of IFX antibodies[52]
IFX	> 2.1 μg/mL at week 14 in UC	Associated with mucosal healing[53]
IFX	≥ 3 μg/mL during maintenance	Clinical remission[48]
IFX	> 3 μg/mL at week 14 or 22 in CD	Sustained response[54]
IFX	3-7 μg/mL during maintenance	Remission[16]
IFX	≥ 7 μg/mL during maintenance	Mucosal healing[48]
IFX	< 7 μg/mL at week 14 in luminal CD	Absence of primary response[53]
IFX	> 9.2 μg/mL at induction week 2 in CD	Fistula response at weeks 14 and 30[56]
IFX	≥ 10 μg/mL at induction week 6	Clinical response[48]
IFX	> 15 μg/mL at week 6 in UC	Associated with mucosal healing[53]
IFX	≥ 20 μg/mL at induction week 2	Clinical response[48]
IFX	≥ 22 μg/mL at week 6 in UC	Clinical response at week 8[55]
IFX	≥ 25 μg/mL at induction week 2	Mucosal healing[48]
Adalimumab (Ada.)
Ada.	≥ 3 μg/mL during maintenance	Clinical response[48]
Ada.	≥ 5 μg/mL post induction (week 14)	Clinical response[48]
Ada.	≥ 7 μg/mL post induction (week 14)	Mucosal healing[48]
Ada.	≥ 8 μg/mL during maintenance	Mucosal healing[48]
Ada.	< 12 μg/mL at week 14 in luminal CD	Absence of primary response[53]
Ustekinumab (UST)
UST	≥ 1 μg/mL during maintenance	Clinical response[48]
UST	≥ 3.5 μg/mL post induction (week 8)	Clinical response[48]
UST	≥ 4.5 μg/mL during maintenance	Mucosal healing[48]
Vedolizumab (VDZ)
VDZ	≥ 12 μg/mL during maintenance	Clinical response[48]
VDZ	≥ 14 μg/mL during maintenance	Mucosal healing[48]
VDZ	≥ 15 μg/mL post induction (week 14)	Clinical response[48]
VDZ	≥ 17 μg/mL post induction (week 14)	Mucosal healing[48]
VDZ	≥ 24 μg/mL at induction (week 6)	Clinical response[48]
VDZ	≥ 28 μg/mL at induction (week 2)	Clinical response[48]

Many studies that looked at exposure response relationship studies of anti-tumor necrosis factor drugs have demonstrated that specific drug concentration thresholds are associated with certain clinical outcomes, such as clinical response, improvement in biochemical markers, endoscopic remission, and mucosal healing.