1. Clinical Overview
Mesalazine (5-aminosalicylic acid or 5-ASA) is a first-line, locally acting anti-inflammatory aminosalicylate drug primarily used for the treatment of mild to moderate ulcerative colitis and maintenance of remission. It acts topically on the colonic mucosa to reduce inflammation. In the Indian context, it is a cornerstone therapy for inflammatory bowel disease (IBD), available in various oral and rectal formulations.
| Onset | Duration | Bioavailability |
|---|---|---|
| Therapeutic effect for induction of remission typically begins within 2-4 weeks of starting therapy. Symptomatic relief (e.g., reduced diarrhea) may be seen earlier. | The anti-inflammatory effect is sustained as long as therapeutic concentrations are maintained at the colonic mucosa. For maintenance therapy, continuous daily dosing is required. | Oral bioavailability is highly formulation-dependent. For pH-dependent delayed-release tablets (e.g., Asacol), it is approximately 20-30%. For sustained-release formulations, it is designed to be minimal in the upper GI tract, with primary release in the colon. |
2. Mechanism of Action
Mesalazine's primary mechanism is topical anti-inflammatory action on the colonic mucosa. It is a prodrug/site-specific agent that acts locally. Its exact mechanism is multifactorial: it inhibits cyclooxygenase and lipoxygenase pathways, reducing prostaglandin and leukotriene synthesis; scavenges reactive oxygen species; inhibits neutrophil chemotaxis and degranulation; and interferes with nuclear factor kappa B (NF-κB) activation, thereby reducing the production of pro-inflammatory cytokines (TNF-α, IL-1, IL-6).
3. Indications & Uses
- Treatment of mild to moderate active ulcerative colitis
- Maintenance of remission in ulcerative colitis
4. Dosage & Administration
Adult Dosage: Active Disease: 2-4.8 g/day in 2-3 divided doses. Common Indian regimen: 500mg tablets: 4-6 tablets per day (2-3 g/day). Maintenance: 1.5-3 g/day in 2-3 divided doses. Common: 2-4 tablets per day (1-2 g/day).
Administration: Swallow tablets whole with a full glass of water; do NOT crush, chew, or break. Take with or after food to reduce GI upset. For pH-dependent tablets (e.g., Asacol), consistency in timing relative to meals is important. Do not take antacids within 1-2 hours of dose as they may alter pH-dependent release.
5. Side Effects
Common side effects may include:
- Headache
- Nausea, vomiting, dyspepsia
- Abdominal pain
- Diarrhea (may mimic disease flare)
- Flatulence
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Warfarin | Mesalazine may potentiate anticoagulant effect, increasing INR and bleeding risk. | Major |
| Azathioprine / 6-Mercaptopurine | Concurrent use may increase risk of blood dyscrasias (leukopenia, pancytopenia). | Major |
| Non-Steroidal Anti-Inflammatory Drugs (NSAIDs) | May increase risk of nephrotoxicity (additive renal effects). | Major |
| Lactulose | May lower colonic pH, potentially affecting release of pH-dependent mesalazine formulations. | Moderate |
| Thiopurine Methyltransferase (TPMT) Inhibitors | May alter metabolism of thiopurines if used concurrently, increasing toxicity risk. | Moderate |
| Digoxin | Mesalazine may reduce absorption of digoxin. | Moderate |
7. Patient Counselling
- DO swallow the tablet whole with plenty of water.
- DO take it regularly, even when you feel well, if on maintenance therapy.
- DO inform all your doctors and dentists you are taking this medicine.
- DO keep all scheduled blood (CBC, creatinine) and urine tests.
- DON'T crush, chew, or break the tablet.
- DON'T take antacids at the same time.
- DON'T stop taking the medicine suddenly without consulting your doctor, even if symptoms improve.
8. Toxicology & Storage
Overdose: Acute overdose may cause severe nausea, vomiting, diarrhea, abdominal pain, tinnitus, vertigo, headache, hyperventilation, sweating, tachycardia, drowsiness, confusion, and metabolic acidosis. High doses can lead to renal failure and CNS effects (convulsions, coma).
Storage: Store below 30°C in a cool, dry place, protected from light and moisture. Keep the bottle tightly closed. Keep out of reach of children. Do not use after the expiry date printed on the pack.