BACKGROUND AND AIMS: Golimumab has been approved recently to treat refractory 
moderate-to-severe ulcerative colitis [UC]. To date it is not clear why a 
considerable fraction of patients do not respond, or lose initial response, to 
golimumab therapy. Our aim was to investigate whether a low golimumab serum 
concentration and/or a positive anti-golimumab antibody status reduces the 
efficacy of this drug in patients with UC.
METHODS: Serum samples of 21 patients with moderate-to-severe UC were collected 
during the first 14 weeks of golimumab therapy. For measurement of golimumab 
serum concentrations, both a tumour necrosis factor [TNF]-coated enzyme-linked 
immunosorbent assay [ELISA] and a sandwich-type ELISA were developed. 
Anti-golimumab antibodies were measured using a bridging ELISA and a 
newly-developed drug-tolerant immunoassay. Clinical response and mucosal healing 
were assessed 14 weeks after start of treatment.
RESULTS: Out of 21 patients, 10 [48%] reached partial clinical response at Week 
14. Median [interquartile range] serum golimumab concentration was significantly 
higher in partial clinical responders than in non-responders: 10.0 [7.8-10.5] 
µg/ml versus 7.4 [4.8-8.3] µg/ml at Week 2 [p = 0.035] and 5.1 [4.0-7.9] µg/ml 
versus 2.1 [1.8-4.2] µg/ml at week 6 [p = 0.037]. Four out of 21 UC patients 
developed anti-golimumab antibodies, detectable only using a drug-tolerant 
immunoassay, and three had a partial clinical response at that time. Clinical 
non-responders had a significantly more severe colitis, indicated by a higher 
endoscopic Mayo score at baseline compared with partial clinical responders [p = 
0.048].
CONCLUSION: Adequate exposure to golimumab drives clinical response. A worse 
disease at baseline influences clinical response rate negatively.