IBD it's types of it's subtypes which are important in term of pharmacotherapy
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I now have comprehensive content on all major IBD drug classes. Let me compile the full answer.
IBD: Types, Subtypes, and Pharmacotherapy
What is IBD?
Inflammatory Bowel Disease (IBD) is a spectrum of remitting and relapsing, chronic inflammatory intestinal conditions causing diarrhea, abdominal pain, bleeding, anemia, and weight loss. It is conventionally divided into two major subtypes: Ulcerative Colitis (UC) and Crohn's Disease (CD), with a lesser-recognized third entity, Microscopic Colitis. (Goodman & Gilman's, p. 1130)
The Two Major Subtypes
1. Ulcerative Colitis (UC)
| Feature | Detail |
|---|---|
| Location | Colon only - starts at anal verge, extends proximally |
| Depth | Mucosal/superficial inflammation |
| Pattern | Confluent (continuous), no skip lesions |
| Extent | Proctitis → left-sided colitis → pancolitis |
| Histology | Lymphocytic + neutrophilic infiltrates |
| Cytokine profile | TH2-type (IL-4, IL-13) |
| Curative surgery? | YES - colectomy is curative |
| CRC risk | Elevated after 7-8 years of disease |
2. Crohn's Disease (CD)
| Feature | Detail |
|---|---|
| Location | Any part of GI tract - most commonly ileocecal region |
| Depth | Transmural (full-thickness) inflammation |
| Pattern | Skip areas of normal mucosa |
| Complications | Strictures, fistulas, abscesses |
| Histology | Lymphocytes, macrophages, granuloma formation, submucosal fibrosis |
| Cytokine profile | TH1-type (IL-12, IL-23, IFN-γ, TNF-α) |
| Curative surgery? | NO - surgery is not curative |
| CRC risk | 4-20x general population risk |
Classifications of Drugs to Treat IBD
(Goodman & Gilman's Chapter 55, p. 1130-1138)
Class 1 - Mesalamine (5-ASA)-Based Therapy
The first-line for mild-to-moderate UC. Largely abandoned in Crohn's disease because the anti-inflammatory effects are topical/mucosal and have limited effect on the deeper (transmural) inflammation of CD.
| Drug | Mechanism | Formulation/Site of Release | IBD Use |
|---|---|---|---|
| Sulfasalazine | Prodrug: azo bond cleaved by colonic bacteria → 5-ASA (active) + sulfapyridine (carrier) | Released in colon | UC (mild-moderate); CD arthritis |
| Mesalamine (oral) | NF-κB inhibition, COX inhibition, free radical scavenging | Various pH-dependent release formulations to reach ileum/colon | UC induction + maintenance |
| Mesalamine (topical) | Same | Suppository, enema | Distal UC/proctitis |
| Olsalazine | Two 5-ASA molecules linked by azo bond | Colonic cleavage | UC |
| Balsalazide | 5-ASA linked to carrier (4-aminobenzoyl-β-alanine) | Colonic cleavage | UC |
Adverse effects of sulfasalazine (due to sulfapyridine component): headache, nausea, hemolytic anemia, oligospermia, hypersensitivity. The newer 5-ASA formulations avoid these by eliminating sulfapyridine.
Class 2 - Glucocorticoids
Indicated for moderate-to-severe IBD - both UC and CD. Used for induction of remission only, not maintenance (due to side effects and failure to maintain remission).
Patient response categories:
- Glucocorticoid-responsive - improve within 1-2 weeks, remain in remission on taper
- Glucocorticoid-dependent - respond but relapse on taper → shift to immunomodulators/biologics
- Glucocorticoid-resistant - do not respond at all → biologics required
| Drug | Key Pharmacology | Notes |
|---|---|---|
| Prednisone | Oral/IV; 40-60 mg/day initial; t½ ~3.5h (converted to prednisolone in liver) | Most common; taper 5 mg/week after response |
| Budesonide | High first-pass metabolism (CYP3A4); bioavailability 9-21%; t½ 2-3.6h | Preferred for mild-moderate ileal/right-sided CD - fewer systemic SE; also useful in UC |
| Triamcinolone | Oral; bioavailability ~90%; t½ 3-5h but receptor effect ~36h | For acute flares; no significant mineralocorticoid activity |
Adverse effects: Cushingoid features, skin thinning, osteoporosis, hypertension, hyperglycemia, psychiatric effects, HPA axis suppression.
Class 3 - Immunomodulatory Agents (Thiopurines + Methotrexate)
Used for steroid-dependent or steroid-resistant IBD, as steroid-sparing agents, and to maintain remission. Onset of action is slow (weeks to months).
Thiopurines
| Drug | Dose | Notes |
|---|---|---|
| Azathioprine (AZA) | 1.5-2.5 mg/kg/day | Prodrug → 6-mercaptopurine → 6-thioguanine nucleotides (active) |
| 6-Mercaptopurine (6-MP) | 1.5-2.0 mg/kg/day | Active sooner than AZA |
Metabolism pathway - three competing fates:
- XO → 6-thiouric acid (inactive)
- TPMT → 6-MMP (potentially hepatotoxic)
- HGPRT → 6-thioguanine nucleotides (active, also myelotoxic at high levels)
Critical pharmacogenomics point: TPMT polymorphism affects toxicity - ~1 in 300 have minimal TPMT activity → all drug shunted to 6-TGN → severe myelosuppression. Testing TPMT activity before starting therapy is recommended.
Uses: Maintain remission in both UC and CD; prevent postoperative CD recurrence; treat CD fistulas. Combined with infliximab, AZA is more effective than infliximab alone for mucosal healing.
Methotrexate
Used in CD (especially steroid-dependent CD); less evidence in UC. Inhibits dihydrofolate reductase → anti-inflammatory via adenosine pathway. Key adverse effects: hepatotoxicity (monitor LFTs), pneumonitis, teratogenicity (contraindicated in pregnancy).
Class 4 - Biological Therapies (Monoclonal Antibodies)
For moderate-to-severe IBD failing conventional therapy.
A. Anti-TNF-α Agents
| Drug | Route | Induction Dose | Maintenance | UC | CD |
|---|---|---|---|---|---|
| Infliximab (chimeric IgG1) | IV | 5 mg/kg at wks 0,2,6 | 5 mg/kg q8wks | ✓ | ✓ |
| Adalimumab (fully human) | SC | 160 mg, then 80 mg at wk2 | 40 mg q2wks | ✓ | ✓ |
| Certolizumab pegol (PEGylated Fab') | SC | 400 mg at wks 0,2,4 | 400 mg q4wks | - | ✓ |
| Golimumab (fully human) | SC | 200 mg, then 100 mg at wk2 | 100 mg q4wks | ✓ | - |
Important adverse effects of anti-TNF agents:
- Risk of serious infections (bacterial, fungal, opportunistic)
- TB reactivation - mandatory TB screening (PPD/IGRA) before starting
- Acute infusion reactions (infliximab) or injection site reactions
- Anti-drug antibody formation (most with infliximab due to chimeric nature)
- Contraindicated in severe CHF (infliximab)
- Possible increased risk of lymphoma
Mechanism note: Infliximab also binds membrane-bound TNF-α, causing lysis of TNF-expressing cells (antibody-dependent cytotoxicity) - this may explain its prolonged effect and efficacy in fistulizing CD.
B. Anti-Integrin Agents
| Drug | Target | Indication |
|---|---|---|
| Vedolizumab | α4β7 integrin (gut-selective) | Moderate-severe UC and CD |
| Natalizumab | α4 integrin (non-selective) | CD (restricted use due to PML risk) |
| Etrolizumab | β7 integrin | Phase III trials for UC/CD |
Vedolizumab - 300 mg IV at wks 0,2,6 then q8wks. Gut-selective mechanism means fewer systemic immune adverse effects than anti-TNF agents. Preferred when anti-TNF therapy has failed or is contraindicated.
Natalizumab - blocks leukocyte trafficking to gut AND brain → risk of Progressive Multifocal Leukoencephalopathy (PML) due to JC virus reactivation. Use restricted to CD refractory to other treatments with JC antibody testing required.
C. Anti-IL-12/23 Agent
| Drug | Target | Indication |
|---|---|---|
| Ustekinumab (fully human) | p40 subunit of IL-12 + IL-23 | Moderate-severe CD (also UC) |
Induction: IV 260-520 mg (weight-based). Maintenance: 90 mg SC q8wks. Long t½ (up to 120 days). Originally developed for psoriasis. Effective for induction and maintenance of remission in CD.
Class 5 - Small-Molecule Drugs (JAK Inhibitors)
| Drug | JAK selectivity | Indication |
|---|---|---|
| Tofacitinib | JAK1, JAK2, JAK3, TYK2 (primarily JAK1/3) | Moderate-severe UC |
| Upadacitinib | JAK1-selective | UC and CD |
| Filgotinib | JAK1-selective | UC |
Mechanism: Block JAK-STAT signaling cascade downstream of cytokine receptors → inhibit IL-2, IL-4, IL-6, IL-7, IL-9, IL-15, IL-21 signaling. Oral agents - advantage over biologics. Unlike biologics, do NOT generate neutralizing anti-drug antibodies.
Adverse effects: Increased infections, possible thromboembolism (at high doses), herpes zoster reactivation, lipid changes.
Class 6 - Microbiome-Based Therapies
- Antibiotics (metronidazole, ciprofloxacin): Mainly in CD - treatment of perianal fistulas and pouchitis
- Probiotics: Some evidence in UC maintenance (e.g., VSL#3), limited role in CD
- Fecal Microbiota Transplant (FMT): Emerging role, particularly in recurrent pouchitis after colectomy for UC
Drug Choice by IBD Subtype and Severity
Ulcerative Colitis - Step-up Approach
Mild-Moderate UC
→ 5-ASA (oral ± topical for distal disease)
→ If insufficient: Budesonide MMX or systemic steroids (prednisone)
Moderate-Severe UC
→ IV steroids (acute) or oral steroids
→ Add immunomodulator (AZA/6-MP) if steroid-dependent
→ Biologics: Anti-TNF (infliximab preferred), vedolizumab, ustekinumab
→ JAK inhibitor (tofacitinib, upadacitinib)
Refractory/Severe UC
→ IV cyclosporine or IV infliximab (rescue therapy)
→ Colectomy (curative)
Crohn's Disease - Key Differences from UC
5-ASA: NOT effective for maintaining CD remission
Mild-Moderate CD
→ Budesonide (ileocecal disease)
Moderate-Severe CD
→ Systemic steroids (induction) + immunomodulators (AZA/6-MP/MTX)
→ Anti-TNF agents (infliximab, adalimumab, certolizumab)
→ Vedolizumab
→ Ustekinumab (particularly if prior anti-TNF failure)
→ Upadacitinib (JAK1 inhibitor)
Fistulizing CD
→ Infliximab (best evidence)
→ AZA/6-MP as adjunct
→ Antibiotics (metronidazole/ciprofloxacin)
Third Subtype: Microscopic Colitis
Two forms: Collagenous Colitis and Lymphocytic Colitis. Presents with chronic watery, non-bloody diarrhea; normal colonoscopy but abnormal biopsies. Pharmacotherapy:
- Budesonide is the primary treatment (most evidence)
- Stop offending medications (NSAIDs, PPIs, SSRIs often implicated)
- Cholestyramine, bismuth, or mesalamine for mild disease
Key Pharmacotherapy Summary Table
| Drug Class | UC | CD | Notes |
|---|---|---|---|
| 5-ASA | First-line (mild-mod) | Not effective for maintenance | UC-specific |
| Budesonide | Moderate UC (MMX formulation) | Mild-mod ileal CD | Low systemic SE |
| Prednisone | Moderate-severe | Moderate-severe | Induction only |
| AZA/6-MP | Steroid-sparing, maintenance | Steroid-sparing, fistulas | Slow onset; check TPMT |
| Methotrexate | Limited | Yes (steroid-dependent) | Teratogenic |
| Infliximab | Yes | Yes | IV; best for fistulas |
| Adalimumab | Yes | Yes | SC; self-administered |
| Certolizumab | No | Yes | PEGylated Fab; safe in pregnancy |
| Golimumab | Yes | No | SC; UC only |
| Vedolizumab | Yes | Yes | Gut-selective; anti-integrin |
| Ustekinumab | Yes | Yes | Anti-IL-12/23 |
| Tofacitinib | Yes | Not approved | Oral JAK inhibitor |
| Upadacitinib | Yes | Yes | Oral JAK1 inhibitor |
Sources: Goodman & Gilman's The Pharmacological Basis of Therapeutics, Chapter 55 (Pharmacotherapy of Inflammatory Bowel Disease), pp. 1130-1138; Sleisenger and Fordtran's Gastrointestinal and Liver Disease
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