Aminosalicylates
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- Widely used in inflammatory bowel disease (IBD) and as a disease-modifying antirheumatic drug (DMARD).
- First developed as a combination of an anti-inflammatory + antibiotic component.
⚗️ Mechanism
- Composed of 5-ASA (mesalazine, anti-inflammatory) bound to sulfapyridine (antibiotic) via an azo bond.
- In the colon, bacterial enzymes split the azo bond → releasing both components.
- 🟢 5-ASA: local anti-inflammatory effect in bowel mucosa.
- 🟠 Sulfapyridine: systemic absorption, responsible for many side effects, but may also contribute to DMARD action.
🔬 Other 5-ASA Formulations (IBD-specific)
- Olsalazine: 2 × 5-ASA molecules linked by azo bond, cleaved in colon.
- Balsalazide: 5-ASA linked to inert carrier molecule, released by colonic bacteria.
- Asacol: Mesalazine with pH-sensitive coating (dissolves at pH 6–7).
- Pentasa: Mesalazine with slow release throughout small bowel → useful in Crohn’s disease.
- Mesalazine (active form): local anti-inflammatory in bowel.
🧠 Mode of Action
- Inhibits COX enzymes and thromboxane A₂ synthesis → ↓ prostaglandins.
- Suppresses plasma cell production of immunoglobulins (↓ IgA, IgM, RF).
- Reduces inflammatory mediators → useful in IBD and arthritis.
📌 Indications
- Ulcerative colitis (induction + maintenance of remission).
- Crohn’s disease (less clear benefit, more for colonic disease).
- Rheumatoid arthritis (as a DMARD).
- Ankylosing spondylitis, psoriatic arthritis, juvenile idiopathic arthritis.
⚠️ Side Effects
- Common: Rash, nausea, headache, anorexia.
- Hematological: ↓ WCC, neutropenia, thrombocytopenia, haemolytic anaemia, methaemoglobinaemia.
- GU: Reversible azoospermia → male infertility (counsel patients).
- Urine: Orange/yellow discolouration.
- Autoimmune: Can induce positive dsDNA antibodies.
- Rare: Pulmonary fibrosis, Stevens–Johnson syndrome, hepatitis.
🔗 Interactions
- Patients who are slow acetylators are at increased risk of toxicity from sulfapyridine.
- Caution with other myelosuppressive drugs (e.g., azathioprine, methotrexate).
💉 Dose
- Start: 500 mg OD → titrate over 2–3 weeks to 2–4 g/day in divided doses.
- Use enteric-coated tablets to reduce GI upset.
🧪 Monitoring
- FBC & LFTs: every 2 weeks for 3 months, then every 3 months long-term.
- Renal function: monitor (risk of nephrotoxicity with 5-ASA compounds).
- Check for G6PD deficiency (risk of haemolysis).
📚 References
