Mesalazine (5-ASA): Anti-Inflammatory for Inflammatory Bowel Disease
Mesalazine (5-aminosalicylic acid, 5-ASA; Asacol, Pentasa, Salofalk) is the active moiety of sulfasalazine — it acts topically in the gut mucosa to reduce inflammation. Unlike sulfasalazine, it avoids the systemic side effects of the sulfapyridine carrier.
First-line treatment for mild-to-moderate ulcerative colitis (UC) — induction and maintenance. Modest role in Crohn's disease (less effective than for UC).
Mechanism of Action
Multiple anti-inflammatory mechanisms: inhibits NF-κB signalling, reduces prostaglandin synthesis (COX inhibition), decreases leukotriene production, scavenges free radicals, and inhibits neutrophil chemotaxis. Acts topically in gut mucosa.
Indications & Use
Mild-to-moderate ulcerative colitis (induction of remission and maintenance), proctitis, left-sided colitis, pancolitis. Multiple formulations target different colonic regions: pH-dependent release (Asacol: ileum/colon), time-release (Pentasa: throughout gut), suppositories/enemas for distal disease.
Dosage
Induction: 2.4–4.8 g/day (oral). Maintenance: 1.6–2.4 g/day. Suppositories 1 g/day for proctitis. High-dose once-daily (2.4 g) as effective as split dosing — improves adherence. Continue maintenance indefinitely to prevent relapse.
Side Effects
Generally well tolerated. Rare: nephrotoxicity (interstitial nephritis — check creatinine at baseline, 3 months, annually). Nausea, diarrhoea (exacerbation). Very rare: hypersensitivity pneumonitis, pericarditis.
Drug Interactions
Azathioprine/6-mercaptopurine: mesalazine inhibits TPMT — increases thiopurine toxicity risk. NSAIDs: additive renal toxicity risk. Anticoagulants (warfarin): may potentiate effect.
Contraindications
Severe renal impairment, severe hepatic impairment, salicylate hypersensitivity (aspirin allergy — cross-sensitivity possible). Caution in pregnancy (safe for most, but use lowest effective dose).
Frequently Asked Questions
How does mesalazine differ from sulfasalazine?
Sulfasalazine consists of mesalazine (5-ASA) linked to sulfapyridine. In the colon, bacteria cleave the bond, releasing mesalazine (active) and sulfapyridine (responsible for side effects: nausea, headache, male infertility, rash). Mesalazine alone avoids these sulfapyridine side effects.
Does mesalazine prevent colorectal cancer?
Evidence suggests long-term mesalazine use in UC is associated with a reduced risk of colorectal cancer (CRC). This chemoprotective effect is thought to result from its anti-inflammatory and antiproliferative properties. Regular colonoscopy surveillance remains essential.
How long should mesalazine maintenance be continued?
Indefinitely, in most patients with UC. Stopping maintenance therapy significantly increases the risk of relapse (about 60% relapse within 12 months without maintenance vs. 20–25% with mesalazine).
References
- ECCO Guidelines UC 2022
- EMA Asacol/Pentasa SPC 2023
- Kornbluth A, Sachar DB. AJG 2010
Medical Disclaimer: This information is for educational purposes only and does not replace professional medical advice.