interleukin 12 and interleukin 23 are inflammatory cytokines implicated in crohn s disease pathophysiology ustekinumab is a monoclonal antibody against the p40 subunit of interleukin 12 23 we performed a double blind cross over trial of the clinical effects of ustekinumab in 104 patients with moderate to severe crohn s disease population 1 patients were given subcutaneous placebo at weeks 0 3 then ustekinumab at weeks 8 11 subcutaneous ustekinumab at weeks 0 3 then placebo at weeks 8 11 intravenous placebo at week 0 then ustekinumab at week 8 or intravenous ustekinumab at week 0 then placebo at week 8 furthermore an open label trial evaluated the effects of 4 weekly subcutaneous injections or 1 intravenous infusion of ustekinumab in 27 patients who were primary or secondary nonresponders to infliximab population 2 in population 1 clinical response rates for the combined groups given ustekinumab and placebo were 53 and 30 p 02 respectively at weeks 4 and 6 and 49 and 40 p 34 respectively at week 8 in a subgroup of 49 patients who were previously given infliximab neither primary nor secondary nonresponders clinical response to ustekinumab was significantly greater than the group given placebo p 05 through week 8 in population 2 the clinical responses at week 8 to subcutaneous and intravenous ustekinumab were 43 and 54 respectively there was no increase in the number of adverse or serious adverse events in patients given ustekinumab through week 8 compared with placebo ustekinumab induced a clinical response in patients with moderate to severe crohn s disease especially in patients previously given infliximab.