Starting an IL-23 Medication for IBD: Induction, Maintenance, and Response Tracking

Starting an IL-23 medication for IBD means committing to a two-stage schedule: a short induction course of high-dose infusions, followed by long-term subcutaneous injections you give yourself at home. The interleukin-23 inhibitors approved for inflammatory bowel disease are risankizumab, sold as Skyrizi, mirikizumab, sold as Omvoh, and guselkumab, sold as Tremfya. Each has its own induction dose, its own maintenance interval, and its own week when the switch happens. Knowing those milestones in advance, and knowing what to record along the way, makes the first year easier to evaluate with your gastroenterologist.

How IL-23 Inhibitors Work and Why Ustekinumab Is Different

Interleukin-23 is a signaling protein built from two subunits, p19 and p40. Ustekinumab, the older drug in this general family, binds the p40 subunit shared by both IL-12 and IL-23, so it blocks two pathways at once. Risankizumab, mirikizumab, and guselkumab bind p19 instead, which is unique to IL-23, leaving IL-12 signaling intact. That distinction matters when reading trial data, because ustekinumab is usually the active comparator rather than a class member.

The regulatory timeline differs by drug. Risankizumab was approved for moderately to severely active Crohn's disease in 2022 and for ulcerative colitis in June 2024, making it the first IL-23-specific inhibitor covering both conditions. Mirikizumab was approved by the FDA on October 26, 2023 for ulcerative colitis and its label now also covers moderately to severely active Crohn's disease. Guselkumab, first approved in 2017 for plaque psoriasis, now carries indications for both moderately to severely active ulcerative colitis and Crohn's disease.

Induction: Three Doses Over Eight Weeks

All three drugs use the same induction rhythm of weeks 0, 4, and 8, but the doses are not interchangeable and differ by diagnosis. For Crohn's disease, risankizumab is given as 600 mg intravenously at weeks 0, 4, and 8; for ulcerative colitis the induction dose is 1,200 mg intravenously on the same schedule. Mirikizumab induction is 300 mg intravenously for ulcerative colitis and 900 mg intravenously for Crohn's disease, each at weeks 0, 4, and 8.

Guselkumab is the one IL-23 inhibitor that can be induced without an infusion. Induction can be 200 mg intravenously at weeks 0, 4, and 8, or 400 mg subcutaneously given as two 200 mg injections on the same three-visit schedule. The subcutaneous route was tested in the GRAVITI trial, where 56.1% of guselkumab-treated Crohn's patients reached clinical remission at week 12 compared with 21.4% on placebo.

Maintenance: The Week 12 Handoff

Week 12 is the pivot point for most patients. Risankizumab maintenance is 180 mg or 360 mg subcutaneously starting at week 12, then every 8 weeks. Mirikizumab maintenance is more frequent, at 200 mg subcutaneously every 4 weeks for ulcerative colitis and 300 mg every 4 weeks for Crohn's disease, both beginning at week 12. Guselkumab offers two maintenance patterns, either 100 mg subcutaneously at week 16 and every 8 weeks thereafter, or 200 mg at week 12 and every 4 weeks, with the label advising the lowest effective dosage.

The practical consequence is a change in where care happens. Induction ties you to an infusion center, while maintenance moves the drug into your refrigerator and makes your specialty pharmacy the critical link. A four-week interval leaves less margin for a shipping delay than an eight-week one.

When to Expect a Response

Trial data give reasonable expectations for the first year. In the Crohn's disease induction trials ADVANCE and MOTIVATE, week 12 CDAI clinical remission with risankizumab 600 mg was 45% in ADVANCE versus 25% on placebo, with endoscopic response at 40% versus 12%. For ulcerative colitis, the risankizumab program reported clinical remission at week 12 in 20.3% of patients versus 6.2% on placebo, rising to 40.2% at week 52 on 180 mg maintenance versus 25.1%.

Guselkumab in ulcerative colitis showed a similar pattern in QUASAR, with clinical remission in 23% at induction week 12 versus 8% on placebo, and 50% at maintenance week 44 on 200 mg every 4 weeks versus 19%. Mirikizumab in Crohn's disease met both coprimary endpoints in VIVID-1, where 45.4% of patients had a week 12 clinical response plus week 52 CDAI remission compared with 19.6% on placebo. Remission rates roughly double between week 12 and week 48 across these programs, so an incomplete response at the end of induction does not necessarily mean the drug has failed.

Head-to-head data exist as well. In the SEQUENCE trial, risankizumab produced clinical remission at week 24 in 58.6% of Crohn's patients versus 39.5% with ustekinumab, and guselkumab was superior to ustekinumab at week 48 across multiple endpoints in GALAXI-2 and GALAXI-3.

What to Track From the First Dose

Three categories of information make the week 12 and week 52 conversations concrete. The first is symptoms, specifically daily stool frequency, rectal bleeding, abdominal pain, and urgency, because these are the same components that define clinical remission in the trials your gastroenterologist is comparing you against.

The second is laboratory results. The American Gastroenterological Association suggests combining biomarkers with symptoms rather than symptoms alone when monitoring ulcerative colitis, using fecal calprotectin under 150 micrograms per gram to rule out active inflammation. The parallel Crohn's disease guidance uses fecal calprotectin above 150 micrograms per gram or CRP above 5 mg/L to rule in active inflammation.

The third is access dates: each infusion, the week 12 transition, prior authorization approval and expiration, pharmacy shipments, and any dose given late. A gap between doses is easy to forget and hard to reconstruct months later, yet it is often the first thing worth checking when symptoms return.

Safety Monitoring During Induction and Beyond

Screening happens before the first dose. The risankizumab label directs clinicians to evaluate for tuberculosis infection and to obtain liver enzymes and bilirubin before initiating treatment in IBD patients, with continued monitoring through induction. Guselkumab likewise requires baseline liver enzyme and bilirubin evaluation. Mirikizumab labeling flags serious hypersensitivity reactions including anaphylaxis, increased infection risk, tuberculosis, hepatotoxicity, and avoidance of live vaccines.

Common adverse reactions across these labels include upper respiratory infections, joint pain, headache, injection site reactions, and abdominal pain. Logging when a side effect started and how close it fell to a dose gives your care team something more useful than a general impression.

An IL-23 inhibitor is a commitment measured in years, and the record built during the first twelve months becomes the baseline every later decision is compared against. Dates of infusions and injections, the symptoms present at week 12 and week 52, and the calprotectin and CRP values alongside them tell a clearer story than any single clinic visit can, and they turn the question of whether the drug is working into something answerable with evidence.