Biologics and small molecules in IBD

01Purpose and principlesWhat the treatment does and how it fits into care.

Biologics are large parenteral molecules targeting extracellular inflammatory pathways. Anti-TNF agents include infliximab and adalimumab; vedolizumab targets gut lymphocyte trafficking; ustekinumab targets IL-12/23; newer agents selectively target IL-23. Small molecules are oral and have shorter pharmacokinetic persistence but broader systemic considerations: JAK inhibitors alter intracellular cytokine signalling, while S1P modulators reduce lymphocyte egress. NICE appraisals define funded populations and sequencing, and biosimilar availability changes cost. The prescriber must verify the live appraisal and product information rather than relying on a memorised list.

Selection is a shared risk-benefit decision. Perianal fistulising Crohn disease may favour anti-TNF after drainage and seton care. Coexisting axial inflammation or uveitis may influence class choice, while some gut-selective therapies may not treat systemic manifestations. Rapid severe UC may favour a fast-onset option, but thrombosis or cardiovascular risk can make an oral JAK inhibitor inappropriate. Pregnancy experience differs between agents and planned conception should be discussed before switching stable control. After starting, measure symptoms and objective inflammation early, optimise adherence and exposure where evidence supports it, then switch mechanism rather than perpetuating ineffective immunosuppression.

Key points

Advanced IBD therapy includes anti-TNF, anti-integrin, interleukin-targeted biologics, Janus kinase inhibitors and sphingosine-1-phosphate modulators; licensed and NICE-funded choices change frequently.
Choose from disease, location, fistulising or extra-intestinal phenotype, previous exposure, required speed, pregnancy plans, comorbidity, route, adherence and patient preference rather than a fixed universal ladder.
Before treatment, confirm objective inflammation and screen tuberculosis, hepatitis and other relevant infection, vaccination status, malignancy history and class-specific cardiovascular or thrombotic risk.
Anti-TNF therapy has strong experience in severe luminal and fistulising Crohn disease, but undrained abscess or uncontrolled infection must be treated before immunosuppression.
Vedolizumab is gut-selective in mechanism, while ustekinumab and selective IL-23 therapies target cytokine pathways; onset and effectiveness vary by disease and previous drug exposure.
Oral JAK inhibitors can act rapidly but MHRA class warnings require special caution in older people, smokers and those with cardiovascular, malignancy, venous-thromboembolism or serious infection risk.
Primary non-response, pharmacokinetic loss, immunogenicity and mechanistic failure need different responses; therapeutic drug monitoring is most established for anti-TNF medicines.
Do not continue expensive or hazardous treatment without an agreed objective induction endpoint, maintenance monitoring and a plan for infection, surgery, pregnancy and vaccination.

02Indications, selection and cautionsWho may benefit, who needs urgent treatment and important alternatives.

Primary non-response

Objective inflammation fails to improve during a complete induction despite adequate administration, suggesting the pathway may not be driving disease or exposure is insufficient.

Secondary loss of response

Initial objective benefit fades during maintenance because of immunogenicity, low drug exposure, non-adherence, infection, structural damage or true mechanistic escape.

Serious infection

Fever, focal symptoms, shingles, opportunistic infection or sepsis may be muted by immune therapy and requires prompt investigation before the next dose.

Infusion or injection reaction

Urticaria, wheeze, hypotension, fever or delayed arthralgia around administration needs severity-based acute care and later assessment of antibodies, excipients and rechallenge risk.

JAK-associated hazard

New chest pain, focal neurology, unilateral limb swelling, dyspnoea, shingles or serious infection during JAK inhibition requires urgent assessment and treatment interruption.

Paradoxical inflammation

Anti-TNF treatment can paradoxically provoke psoriasis-like skin disease and, rarely, other immune phenomena; distinguish this from allergy or infection before abandoning effective IBD control.

Red flags requiring action

Never start or continue an advanced immune therapy through uncontrolled sepsis, untreated active tuberculosis, major opportunistic infection or an undrained Crohn abscess.
Acute dyspnoea, pleuritic pain, leg swelling, myocardial or neurological symptoms on a JAK inhibitor needs emergency thrombotic and cardiovascular assessment.
Disseminated shingles, severe primary varicella or neurological infection in an immunosuppressed patient requires urgent antiviral and specialist management.
New jaundice or marked transaminitis may represent viral hepatitis reactivation, drug injury or another hepatobiliary emergency and should not wait for routine infusion review.
Anaphylaxis during infusion requires immediate emergency treatment; do not simply slow the infusion and continue without severity assessment.

03Assessment before treatmentTests and checks that guide safe selection.

Investigation order

Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.

01
Objective disease activity assessmentFirst step
Why
Confirm that active inflammation justifies escalation and provide a response baseline.
Interpretation and limitations
Use calprotectin, CRP, endoscopy or phenotype-appropriate imaging; active symptoms from fibrosis, infection or functional disease will not necessarily improve with stronger immunosuppression.
02
Tuberculosis screening
Why
Identify active or latent infection before therapies that can permit reactivation.
Interpretation and limitations
Combine history, exposure, chest imaging and interferon-gamma or local testing; immunosuppression can cause false-negative tests, and suspected active disease needs specialist exclusion.
03
Hepatitis B, hepatitis C and HIV screen
Why
Detect infection that changes prophylaxis, treatment choice and monitoring.
Interpretation and limitations
Interpret hepatitis surface antigen, core antibody and surface antibody together; isolated core positivity may still carry reactivation risk and merits hepatology or virology advice.
04
Full blood count, renal, liver and lipid profile
Why
Create class-specific safety baselines and identify contraindications.
Interpretation and limitations
Cytopenia or liver injury affects most options, while lipids, renal function and cardiovascular assessment are particularly important for selected oral small molecules.
05
Anti-TNF trough concentration and antibodies
Why
Investigate objectively confirmed secondary loss of response.
Interpretation and limitations
Low exposure without antibodies may support pharmacokinetic optimisation, high antibodies may support a class or agent change, and adequate exposure with inflammation suggests mechanistic failure.
06
Pregnancy and vaccination review
Why
Align treatment timing with conception, infant exposure and preventable infection.
Interpretation and limitations
Check live-vaccine implications for the patient and exposed infant using current UK specialist guidance; avoid destabilising effective disease control through unplanned cessation.

04Treatment approachPreparation, options, escalation and aftercare.

01SELECTChoose a mechanism, not merely a brandFirst stepModerate to severe objective IBD activity needs advanced steroid-sparing therapy.

1Confirm diagnosis, inflammatory target, luminal versus fistulising phenotype, previous drug response, need for speed and whether surgery or drainage better addresses structural disease.
2Screen infection, vaccination, malignancy, cardiovascular and thrombosis risk, organ function, pregnancy plans and medicine interactions before narrowing the class choice.
3Compare current NICE-funded efficacy, safety, route, monitoring, extra-intestinal effect, infusion access and patient priorities through specialist shared decision-making.
4Document induction regimen, treatment target, assessment date, maintenance plan and what symptoms require withholding treatment or contacting the IBD service.

02STARTInitiate with complete safeguardsA specific biologic or small molecule has been selected and current commissioning criteria are met.

1Complete tuberculosis and viral screening, baseline bloods and vaccinations, treating latent or active infection through the relevant specialist pathway.
2Reconcile concurrent immunomodulators and corticosteroid taper, assessing whether combination therapy benefits outweigh age, infection and malignancy risk.
3Provide written administration, missed-dose, storage, travel, infection, surgery, pregnancy and urgent-contact advice appropriate to the exact medicine.
4Arrange early clinical and objective induction review rather than defaulting directly to long-term repeat prescriptions.

03OPTIMISEExplain loss of responseSymptoms recur after an initial response to an advanced treatment.

1Verify administration and adherence, exclude infection and structural complications, and confirm inflammatory recurrence using biomarker, endoscopy or imaging.
2For anti-TNF and selected other classes, obtain properly timed drug and antibody testing when the result will guide a pharmacokinetic or immunogenic decision.
3Optimise dose or interval only when underexposure is plausible and supported, change within class for selected immunogenicity, or switch mechanism for adequate-exposure failure.
4Reassess after the change against a defined target and discuss surgery if focal damage or refractory disease makes continued medical cycling low value.

04TOXICITYManage class-specific adverse eventsNew infection, infusion reaction, thrombotic event, cytopenia, liver injury, dermatological or neurological symptoms occur during therapy.

1Assess severity and withhold the next dose of a clinically significant suspected culprit while contacting the prescribing IBD or acute medical team.
2Treat anaphylaxis, sepsis, thrombosis, severe zoster or organ failure through the emergency pathway before debating long-term IBD alternatives.
3Identify infection, paradoxical inflammation, disease manifestation and unrelated illness using targeted tests; not every symptom represents drug allergy.
4Decide restart, prophylaxis, class switch or permanent withdrawal from severity, causality, remaining options and disease risk, documenting advice across all prescribers.

05Regimens, contraindications and interactionsTreatment details and the circumstances that modify them.

Anti-TNF treatment for moderate to severe luminal and fistulising Crohn disease and active UC, including selected rescue use.

Infliximab

Weight-based intravenous induction and maintenance using the licensed specialist protocol.

Screen tuberculosis and hepatitis; avoid active serious infection, monitor infusion reaction, heart failure, demyelination, immunogenicity, skin cancer and combination-immunosuppression risk.

Gut-selective anti-integrin therapy for moderate to severe UC or Crohn disease after specialist selection.

Vedolizumab

Intravenous or subcutaneous induction and maintenance according to the licensed formulation.

Assess infection and liver symptoms, confirm ongoing response and remember that gut selectivity may not control systemic extra-intestinal disease; route switching follows product guidance.

Targets IL-12/23 or selective IL-23 pathways in eligible moderate to severe Crohn disease or UC.

Interleukin-targeted biologic

Agent-specific parenteral induction followed by scheduled subcutaneous specialist maintenance therapy.

Indications differ by molecule and evolve; screen infection and tuberculosis, monitor liver or hypersensitivity risks from the SmPC and verify current NICE commissioning.

Offers rapid systemic pathway inhibition for eligible moderate to severe UC and selected Crohn disease indications.

Janus kinase inhibitor

Oral induction then maintenance regimen selected by disease response and risk.

Apply MHRA restrictions for age, smoking, cardiovascular disease, malignancy and thrombosis; screen infection, vaccinate against zoster where appropriate and monitor blood, liver and lipids.

Reduces lymphocyte trafficking for eligible moderate to severe ulcerative colitis.

S1P receptor modulator

Oral titration and maintenance schedule following the exact licensed product instructions.

Cardiac conduction, macular oedema, liver injury, lymphopenia, infection, blood pressure and rebound considerations require product-specific baseline and follow-up assessment.

06Complications, monitoring and follow-upAdverse effects, response and longer-term review.

Confirm induction response using symptoms plus objective inflammation within the agent-appropriate period; discontinue or change therapy when the agreed benefit is absent.
At every dose or prescription, screen interval infection, antibiotics, planned surgery, pregnancy, vaccination, new malignancy and class-specific symptoms.
Follow blood count and liver testing for most agents, adding lipids, renal, ECG, ophthalmic or other surveillance according to the small-molecule SmPC and individual risk.
For anti-TNF loss of response, use properly timed levels and antibodies only after inflammation is confirmed and adherence or infection assessed.
Record biosimilar and formulation accurately across pharmacy, infusion, inpatient and patient-held records to prevent duplicated or missed dosing.
Review corticosteroid withdrawal, nutrition, extra-intestinal disease, quality of life and surgical options rather than treating biomarker normalisation as the sole outcome.

07Special situationsVariants, exceptions and circumstances that change the usual approach.

Fast onset has a trade-off

An oral small molecule may act quickly and clear faster, but systemic pathway inhibition introduces cardiovascular, thrombotic, infectious and reproductive considerations absent from convenience alone.

Gut selectivity is contextual

A bowel-selective mechanism can be attractive for systemic safety, but it may leave axial, skin or eye inflammation needing separate control.

Abscess is not drug failure

Fistulising Crohn disease with a collection first requires drainage and sepsis care. Escalating immune therapy before source control answers the wrong problem.

Immunogenicity is actionable

Neutralising antibodies can lower anti-TNF exposure, particularly after interruptions. Accurate drug history and levels can avoid a blind mechanism switch.

The live appraisal governs access

NICE recommendations change as new comparisons and prices emerge. Verify current disease, prior-treatment and commercial-arrangement criteria at prescribing time.

Do not destabilise pregnancy planning

Active IBD itself harms pregnancy outcomes. Changes around conception need joint IBD and obstetric medicine advice rather than reflex withdrawal of every immune therapy.

08Common pitfallsFrequent interpretation and management errors.

01
Choosing an advanced therapy from route or advertising familiarity without confirming phenotype, objective inflammation and comparative safety.
02
Starting anti-TNF treatment for perianal Crohn disease before draining a collection and coordinating seton management.
03
Using a JAK inhibitor without documenting smoking, cardiovascular, thrombotic, malignancy and serious infection risk under MHRA advice.
04
Continuing maintenance indefinitely after a complete primary non-response because the induction prescription is already authorised.
05
Calling symptoms loss of response without excluding infection, non-adherence, bile-acid diarrhoea or a fixed stricture.
06
Interpreting an anti-TNF trough concentration without dose timing, antibody result and objective inflammatory evidence.
07
Stopping effective treatment abruptly for planned pregnancy without specialist counselling on maternal disease risk and infant vaccination.