Source: Health Products Regulatory Authority (ZA) Revision Year: 2022 Publisher: PHARMACARE LIMITED, Healthcare Park, Woodlands Drive, Woodmead, 2191
Category and Class: A 3.1 Antirheumatics (anti-inflammatory agents) Pharmacotherapeutic group: Anti-inflammatory and antirheumatic products, nonsteroids, acetic acid derivatives and related substances.
ATC code: M01AB01
Indomethacin has analgesic, anti-inflammatory and antipyretic properties. Like the salicylates and related anti-inflammatory medicines, indomethacin inhibits the biosynthesis of prostaglandins; this action may be the basis of its antiinflammatory and antipyretic properties and certain of its other effects. Since indomethacin is an inhibitor of prostaglandin synthesis, its mode of action may be due to a decrease of prostaglandins in peripheral tissues. It inhibits motility of polymorphonuclear leucocytes and like salicylates, it uncouples oxidative phosphorylation in supratherapeutic concentrations and depresses the biosynthesis of mucopolysaccharides.
Indomethacin affords relief of symptoms; it does not alter the course of the underlying disease.
Following a single oral dose, indomethacin is readily absorbed from the gastrointestinal tract, attaining peak plasma concentrations of approximately 1 and 2 mcg/mL, respectively, at about 2 hours. Orally administered indomethacin is virtually 100% bioavailable, with 90% of the dose absorbed within 4 hours.
Indomethacin exists in the plasma as the parent medicine and its dimethyl, desbenzoyl, and desmethyl-desbenzoyl metabolites, all in the unconjugated form. About 60% of an oral dosage is recovered in urine as medicine and metabolites (26% as indomethacin and its glucuronide), and 33% is recovered in faeces (1,5% as indomethacin).
Peak plasma concentrations are reached about 2 hours after a dose. About 99% of indomethacin is bound to plasma proteins and indomethacin is distributed into synovial fluid, the central nervous system and the placenta. Low concentrations can be detected in breast milk.
Equal fractions of indomethacin are eventually absorbed following I.M. or oral administration. However, indomethacin is significantly more rapidly absorbed following I.M. administration with peak plasma levels appearing one hour sooner than following oral administration.
Indomethacin is eliminated via renal excretion, metabolism, and biliary excretion. Indomethacin undergoes appreciable enterohepatic circulation. The mean half-life of indomethacin is estimated to be about 4,5 hours. With a typical therapeutic regimen of 25 or 50 mg three times daily, the steady-state plasma concentrations of indomethacin are an average 1,4 times those following the first dose.
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