indication

For the treatment of active ulcerative proctitis.

pharmacology

Mesalazine (INN, BAN), also known as Mesalamine (USAN) or 5-aminosalicylic acid (5-ASA), is an anti-inflammatory drug used to treat inflammation of the digestive tract (Crohn's disease) and mild to moderate ulcerative colitis. Mesalazine is a bowel-specific aminosalicylate drug that is metabolized in the gut and has its predominant actions there, thereby having fewer systemic side effects. As a derivative of salicylic acid, 5-ASA is also an antioxidant that traps free radicals, which are potentially damaging by-products of metabolism.

mechanism of action

Although the mechanism of action of mesalazine is not fully understood, it appears to be topical rather than systemic. Mucosal production of arachidonic acid metabolites, both through the cyclooxygenase pathways, i.e., prostanoids, and through the lipoxygenase pathways, i.e., leukotrienes and hydroxyeicosatetraenoic acids, is increased in patients with chronic inflammatory bowel disease, and it is possible that mesalazine diminishes inflammation by blocking cyclooxygenase and inhibiting prostaglandin production in the colon.

toxicity

Oral, mouse: LD₅₀ = 3370 mg/kg; Oral, rat: LD₅₀ = 2800 mg/kg; Skin, rabbit: LD₅₀ = >5 gm/kg. There have been no documented reports of serious toxicity in man resulting from massive overdosing with mesalamine. Under ordinary circumstances, mesalazine absorption from the colon is limited.

biotransformation

Rapidly and extensively metabolized, mainly to N-acetyl-5-ASA (Ac-5-ASA) in the intestinal mucosal wall and the liver. Ac-5-ASA is further acetylated (deactivated) in at least 2 sites, the colonic epithelium and the liver.

absorption

20 to 30% absorbed following oral administration. 10 to 35% absorbed from the colon (rectal suppository) - extent of absorption is determined by the length of time the drug is retained in the colon.

half life

The mean elimination half-life was 5 hours for 5-ASA and six hours for N-acetyl-5-ASA following the initial dose. At steady state, the mean elimination half-life was seven hours for both 5-ASA and N-acetyl-5-ASA.

route of elimination

Approximately 28% of the mesalamine in Asacol tablets is absorbed after oral ingestion, leaving the remainder available for topical action and excretion in the feces. It is excreted mainly by the kidney as N-acetyl-5-aminosalicylic acid.

drug interactions

Azathioprine: Mesalazine may increase the toxicity of thiopurine, azathioprine.

Mercaptopurine: Mesalazine may increase the toxicity of thiopurine, mercaptopurine.

Thioguanine: Mesalazine may increase the toxicity of thiopurine, thioguanine.