[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Pharmacology](https://durgical.com/en/pharmacology/) › Inflammatory bowel disease: pathogenesis and treatment # Inflammatory bowel disease: pathogenesis and treatment What Crohn's disease and ulcerative colitis are, why they happen, and how medicines, nutrition and supportive care are combined, in adults and children. Updated Nov 12, 2026 On this page - The basics Key points - Goals and drug classes in brief - Microbiome manipulation - Paediatric IBD - Memory aid - Example drugs - Clinical Pathogenesis: ulcerative colitis versus Crohn's disease - Treatment Supportive therapy - Safety IBD in pregnancy - Study Test yourself - Connections Connections Inflammatory bowel disease (IBD) is chronic, relapsing inflammation of the gut from an abnormal immune response to gut microbes in genetically susceptible people. Ulcerative colitis and Crohn's disease differ in location, depth and cytokine profile, which shapes treatment. This page covers pathogenesis, microbiome-based approaches, supportive care, and IBD in children and in pregnancy; the drug classes have their own pages. ## Key points - Ulcerative colitis: continuous mucosal inflammation of the colon from the rectum upward; Crohn's disease: patchy transmural inflammation anywhere, most often near the ileocaecal valve. - Crohn's disease has a Th1-type profile (IL-12, IL-23, interferon gamma, TNF alpha); ulcerative colitis resembles Th2 (IL-13); Th17 cells matter in both. - Treatment aims to induce and maintain remission and heal the mucosa, not only relieve symptoms. - Probiotics may help ulcerative colitis and pouchitis but show no clear benefit in Crohn's disease; faecal transplant is proven for recurrent C. difficile, not yet for IBD. - Loperamide and antispasmodics help mild disease but are avoided in severe colitis because of toxic megacolon. - In pregnancy, controlling disease activity improves outcomes; mesalazine, glucocorticoids, thiopurines and anti-TNF drugs are used, methotrexate and JAK inhibitors are contraindicated. ## Pathogenesis: ulcerative colitis versus Crohn's disease Both diseases arise from an inappropriate immune response to commensal gut bacteria in people with genetic susceptibility, with environmental factors and a disturbed microbiome (dysbiosis) contributing. Ulcerative colitis is confluent inflammation of the colonic mucosa that starts at the rectum and extends a variable distance (proctitis, left-sided colitis, pancolitis). Crohn's disease is transmural and patchy, can affect any part of the gut and causes strictures, fistulas and abscesses. Their cytokine profiles differ: Crohn's disease is driven by IL-12, IL-23, interferon gamma and TNF alpha (Th1-type), ulcerative colitis resembles a Th2 response with IL-13, and IL-23-driven Th17 cells feed both. These pathways are the targets of anti-TNF, anti-IL-12/23, anti-integrin and JAK-inhibitor therapy. ## Goals and drug classes in brief - Aminosalicylates (mesalazine, sulfasalazine): mainly mild to moderate ulcerative colitis. - Glucocorticoids, including gut-targeted budesonide: induce remission, used short term only. - Thiopurines and methotrexate: steroid-sparing maintenance. - Biologics (anti-TNF, anti-integrin, anti-IL-12/23) and small molecules (JAK inhibitors, S1P receptor modulators): moderate to severe disease. - Antibiotics: abscesses, fistulas and septic complications; surgery treats complications but does not cure Crohn's disease. ## Microbiome manipulation Because dysbiosis is part of IBD, changing the microbiome is an attractive idea. Antibiotics such as metronidazole and ciprofloxacin treat perianal and fistulising Crohn's disease and pouchitis. Probiotics, live bacteria given by mouth, have shown benefit in ulcerative colitis and pouchitis in some studies, but not in Crohn's disease, and colonisation is usually transient. Most are sold as supplements, not approved drugs, and they carry infection risk in very ill or immunosuppressed people. Faecal microbiota transplantation, instilling stool from a screened donor, is an approved option to prevent recurrent C. difficile infection; trials in IBD have given mixed results, and donor material can transmit infections despite screening. ## Supportive therapy - Antidiarrhoeals (loperamide, diphenoxylate) reduce stool frequency and urgency in mild disease, but are contraindicated in severe colitis because they can trigger toxic megacolon. - Antispasmodics such as dicycloverine ease cramps; also avoided in severe disease or suspected obstruction. - Bile-acid sequestrants treat bile-salt diarrhoea after ileal resection. - Iron, folate and vitamin B12 are replaced as needed; calcium and vitamin D help prevent bone loss. - NSAIDs are avoided for pain; cannabis is under study but its benefit is not established. ## Paediatric IBD Children and adolescents are the group with the fastest-rising incidence and often present with more severe disease, sometimes with growth failure, perianal disease or extraintestinal features as the first sign. The same drugs are used as in adults. Exclusive enteral nutrition, a liquid formula as the only food for some weeks, is as effective as glucocorticoids in Crohn's disease and supports growth. Before immunosuppression, vaccination status is reviewed and latent tuberculosis is excluded; inactivated vaccines can be given during treatment, live vaccines are not recommended. ## IBD in pregnancy IBD often affects people of reproductive age. Quiet disease improves fertility and pregnancy outcomes, so the aim is to keep remission while limiting fetal exposure. Mesalazine and glucocorticoids are widely used and generally considered safe; thiopurines have not shown more adverse outcomes; anti-TNF antibodies have a low risk, and certolizumab pegol hardly crosses the placenta. Methotrexate is absolutely contraindicated, and JAK inhibitors are avoided in pregnancy and breastfeeding because of animal teratogenicity and transfer into milk. ## Memory aid UC is Up from the rectum, Unbroken and sUperficial; Crohn's is Cobblestone, Complete thickness and can be anywhere from Cheek to Can. ## Test yourself Think of the answer, then tap the question to see it. ## How does the distribution of inflammation differ between ulcerative colitis and Crohn's disease? UC is continuous and mucosal, from the rectum upward in the colon; Crohn's is patchy and transmural and can affect any part of the gut. ## Why are antidiarrhoeals avoided in severe ulcerative colitis? Slowing the inflamed colon can precipitate toxic megacolon; they are kept for mild disease in selected cases. ## Which IBD drug is absolutely contraindicated in pregnancy? Methotrexate; JAK inhibitors are also avoided in pregnancy and breastfeeding. ## What is the advantage of exclusive enteral nutrition in children with Crohn's disease? It can induce remission as well as glucocorticoids while supporting growth, without steroid side effects. [Add to my cards (4)](https://durgical.app/estudiar/?add=/en/pharmacology/topics/inflammatory-bowel-disease-pathogenesis-and-treatment/) [More Pharmacology questions →](https://durgical.com/en/practice/?f=pharmacology) ## Example drugs - [Mesalazine](https://durgical.com/en/pharmacology/mesalazine/) - [Sulfasalazine](https://durgical.com/en/pharmacology/sulfasalazine/) - [Budesonide](https://durgical.com/en/pharmacology/budesonide/) - [Azathioprine](https://durgical.com/en/pharmacology/azathioprine/) - [Mercaptopurine](https://durgical.com/en/pharmacology/mercaptopurine/) - [Methotrexate](https://durgical.com/en/pharmacology/methotrexate/) - [Infliximab](https://durgical.com/en/pharmacology/infliximab/) - [Adalimumab](https://durgical.com/en/pharmacology/adalimumab/) - [Certolizumab pegol](https://durgical.com/en/pharmacology/certolizumab-pegol/) - [Vedolizumab](https://durgical.com/en/pharmacology/vedolizumab/) - [Ustekinumab](https://durgical.com/en/pharmacology/ustekinumab/) - [Tofacitinib](https://durgical.com/en/pharmacology/tofacitinib/) - [Ozanimod](https://durgical.com/en/pharmacology/ozanimod/) - [Metronidazole](https://durgical.com/en/pharmacology/metronidazole/) - [Ciprofloxacin](https://durgical.com/en/pharmacology/ciprofloxacin/) - [Loperamide](https://durgical.com/en/pharmacology/loperamide/) - [Dicycloverine](https://durgical.com/en/pharmacology/dicycloverine/) - [Cyanocobalamin](https://durgical.com/en/pharmacology/cyanocobalamin/) - [Ferrous sulfate](https://durgical.com/en/pharmacology/ferrous-sulfate/) ## Connections ## Related classes 8 - [Aminosalicylates (5-ASA)](https://durgical.com/en/pharmacology/classes/aminosalicylates/) - [Corticosteroids (glucocorticoids)](https://durgical.com/en/pharmacology/classes/corticosteroids/) - [Antiproliferative immunosuppressants](https://durgical.com/en/pharmacology/classes/antiproliferative-immunosuppressants/) - [TNF inhibitors](https://durgical.com/en/pharmacology/classes/tnf-inhibitors/) - [Interleukin inhibitors](https://durgical.com/en/pharmacology/classes/interleukin-inhibitors/) - [JAK inhibitors](https://durgical.com/en/pharmacology/classes/jak-inhibitors/) - [Antidiarrhoeals](https://durgical.com/en/pharmacology/classes/antidiarrhoeals/) - [Bile acid sequestrants](https://durgical.com/en/pharmacology/classes/bile-acid-sequestrants/) [← All of pharmacology](https://durgical.com/en/pharmacology/) Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given. Sources: [Treatment for Crohn's Disease](https://www.niddk.nih.gov/health-information/digestive-diseases/crohns-disease/treatment) (National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), 2026); [Probiotics: Usefulness and Safety](https://www.nccih.nih.gov/health/probiotics-what-you-need-to-know) (National Center for Complementary and Integrative Health (NCCIH), 2026); [FDA Approves First Orally Administered Fecal Microbiota Product for the Prevention of Recurrence of Clostridioides difficile Infection](https://www.fda.gov/news-events/press-announcements/fda-approves-first-orally-administered-fecal-microbiota-product-prevention-recurrence-clostridioides) (U.S. Food and Drug Administration, 2023). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/pharmacology/topics/inflammatory-bowel-disease-pathogenesis-and-treatment/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/pharmacology/topics/inflammatory-bowel-disease-pathogenesis-and-treatment/