Gastroprotective Pregnancy: B — considered safe; dibutyl phthalate excipient in some preparations may be harmful — use Pentasa or Salofalk in pregnancy

Mesalazine (5-Aminosalicylic Acid)

Brand names: Asacol, Mezavant, Octasa, Pentasa

Adult dose

Dose: Induction of remission (UC): 2.4–4.8g/day. Maintenance: 1.2–2.4g/day

Route: Oral / Rectal (suppository or enema)

Frequency: Once or divided doses daily

Max: 4.8g/day (oral induction)

Distal UC: rectal mesalazine (1g suppository OD or enema at night) superior to oral alone. Brand matters — each formulation releases drug at different intestinal sites. Do not switch brands without specialist advice.

Dose adjustments

Renal

Avoid in moderate to severe renal impairment (GFR <30) — mesalazine nephrotoxicity.

Hepatic

Avoid in severe hepatic impairment.

Clinical pearls

Renal monitoring: check U&E and creatinine at baseline, 3 months, then annually. Stop if creatinine rises — mesalazine nephritis.
Combined oral + rectal therapy is superior to either alone for extensive or left-sided UC.
Formulation matters: Pentasa releases from duodenum; Asacol/Octasa releases in distal ileum/colon; Mezavant: pH-dependent MMX release. Do not freely switch.
Long-term maintenance reduces colorectal cancer risk in UC — continue indefinitely in most patients.

Contraindications

Salicylate hypersensitivity
Severe renal impairment
Active peptic ulcer disease

Side effects

Interstitial nephritis (rare but serious — idiosyncratic)
Nausea, diarrhoea (often overlap with UC symptoms)
Headache
Worsening of colitis (paradoxical — rare)
Blood disorders (rare — agranulocytosis)

Interactions

Azathioprine: mesalazine inhibits TPMT enzyme — increases azathioprine toxicity risk
NSAIDs: additive renal toxicity
Warfarin: may enhance anticoagulant effect

Monitoring

U&E
creatinine (annually)
FBC (annually)
symptom response
stool frequency

Reference: BSG UC Guidelines 2019; NICE NG130 IBD; NICE BNF 84. Verify against your local formulary and the latest BNF before prescribing.

Curated clinical cross-links plus same-class fallbacks.

Calculators

Drugs

Pathways