5-Aminosalicylic Acid (5-ASA)

5-Aminosalicylic Acid (5-ASA) also known as Mesalazine (INN, BAN) or Mesalamine (USAN) is an anti-inflammatory drug used to treat inflammatory bowel disease, such as ulcerative colitis and mild-to-moderate Crohn’s disease. Mesalazine is a bowel-specific aminosalicylate drug that acts locally in the gut and has its predominant actions there, thereby having few systemic side effects.

As a derivative of salicylic acid, mesalazine is also thought to be an antioxidant that traps free radicals, which are potentially damaging byproducts of metabolism.

Mesalazine is the active moiety of sulfasalazine, which is metabolized to sulfapyridine and mesalazine.

Mesalazine is the active component of the prodrug balsalazide along with the inert carrier molecule 4-aminobenzoyl-beta-alanine.

Dosage and Administration

Induction of Remission of Ulcerative Colitis

Adults: PO 2.4 to 4.8 g tablets once daily with a meal for up to 8 wk. PO 1 g controlled-release capsules 4 times daily for up to 8 wk.

Maintenance of Remission of Ulcerative Colitis

Adults: PO 1.6 g delayed-release tablets daily, in divided doses. PO 1.5 g once daily in the morning.

Treatment of Active, Mild to Moderate Distal Ulcerative Colitis, Proctosigmoiditis, or Proctitis

Adults: PR 4 g in 60 ml rectal suspension enema as rectal instillation once a day for up to 6 wk, preferably at bedtime, retained for 8 h.

Treatment of Active, Mild to Moderate Ulcerative Colitis

Adults: PO 800 mg delayed-release tablets 3 times daily (2.4 g/day) for 6 wk. PO 1 g controlled-release capsules 4 times daily for up to 8 wk.

Treatment of Active Ulcerative Proctitis

Adults: PR 1,000 mg rectal suppository once daily at bedtime. Retain suppository in rectum for at least 1 to 3 h for max benefit for up to 6 wk. PR 4 g in 60 ml rectal suspension enema as rectal instillation every day for up to 6 wk, preferably at bedtime, retained for 8 h.

Side effects

Commonly: Diarrhea, Nausea, Cramping, Flatulence.

Uncommonly: Headache, Exacerbation of the colitis, Hypersensitivity reactions (including rash, urticaria aka hives, interstitial nephritis and lupus erythematosus-like syndrome), Hair loss.

Rarely: Acute pancreatitis, Hepatitis, Nephrotic syndrome, Blood disorders (including agranulocytosis, aplastic anaemia, leukopenia, neutropenia, thrombocytopenia), Fever.

Mesalazine avoids the sulfonamide side effects of sulfasalazine (which contains additional sulfapyridine), but carries additional rare risks of Allergic lung reactions, Allergic myocarditis, Methaemoglobinaemia.

Monitoring

As a result of the small risks of kidney, liver and blood disorders, blood tests should be taken before and after starting treatment. Patients are advised to report any unexplained bleeding, bruising, purpura, sore throat, fever or malaise that occurs during treatment so that a full blood count can be urgently taken.