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N797 Therapeutic drug monitoring after thiopurine initiation improves drug efficacy

Dijkstra-Heida W.*1, Smids C.1, van Luin M.2, Huisman-de Waal G.3, de Leest M.1, Horjus Talabur Horje C.1, Wisse J.1, Wahab P.1, Groenen M.1

1Rijnstate Hospital, IBD centre, Gastroenterology and Hepatology, Arnhem, Netherlands 2Rijnstate Hospital, Pharmacy, Arnhem, Netherlands 3IQ healthcare, Radboud Insitute for Health Sciences, Nijmegen, Netherlands


Thiopurines are effective in the maintenance treatment of inflammatory bowel disease (IBD). However, 20–30% of IBD patients discontinue the Thiopurine within 3 months after initiation due to adverse events or failure of therapy. Our aim was to evaluate the protocol of adjusting dose of Thiopurines, based on the level of metabolites (6-TGN and 6-MMP), on the percentage of patients continuing to use the drug.


This is a retrospective cohort study in adult IBD patients. Two groups of 50 patients were compared. Weight based dosage of mercaptopurine (1–1.5 mg/kg)in the control group (2012–2013) was compared to metabolite level based dosage of mercaptopurine in the therapeutic drug monitoring (TDM) intervention group (2015–2016) (Figure 1). Primary outcome was the percentage of patients still using mercaptopurine 3 months after starting the drug. Secondary outcomes were the number of adverse events and the number of IBD patients with a corticosteroid-free clinical remission at 3 months.

Figure 1. Therarpeutic drug monitoring.


Patients characteristics were similar in the two groups. The number of patients using a Thiopurine after 3 months was 92% in the intervention group and 76% in the control group. Adverse events were reported in 46% of patients in the intervention group and in 66% of patients in the control group. Corticosteroid-free after 3 months were 70% of patients in the intervention group and 56% patients in the control group.


We conclude that therapeutic drug monitoring based dosage is superior to weight based dosage at the initiation of Thiopurine therapy. 3 Months after starting treatment, in the therapeutic drug monitored group, more patients still use Thiopurines, less patients have adverse events and more patients are steroid free compared to weight based dosage group. Further evaluation is needed to study effect on long term remission of IBD.