Racecadotril, also known as acetorphan, is an antidiarrheal medication which acts as a peripheral enkephalinase inhibitor.[3] Unlike other opioid medications used to treat diarrhea, which reduce intestinal motility, racecadotril has an antisecretory effect — it reduces the secretion of water and electrolytes into the intestine.[3] It is available in France (where it was first introduced in ~1990) and other European countries (including Germany, Italy, the United Kingdom, Spain, Portugal, Poland, Finland, Russia and the Czech Republic) as well as most of South America and some South East Asian countries (including China, India and Thailand), but not in the United States. It is sold under the tradename Hidrasec, among others.[4]Thiorphan is the active metabolite of racecadotril, which exerts the bulk of its inhibitory actions on enkephalinases.[5]
Medical uses
Racecadotril is used for the treatment of acute diarrhea in children and adults and has better tolerability than loperamide, as it causes less constipation and flatulence.[6][7] Several guidelines have recommended racecadotril use in addition to oral rehydration treatment in children with acute diarrhea.[8]
Contraindications
Racecadotril has no contraindications apart from known hypersensitivity to the substance.[9][10]
Enkephalins are peptides produced by the body that act on opioid receptors with preference for the δ subtype.[11] Activation of δ receptors inhibits the enzyme adenylyl cyclase, decreasing intracellular levels of the messenger molecule cAMP.[7]
The active metabolite of racecadotril, thiorphan, inhibits enkephalinase enzymes in the intestinal epithelium with an IC50 of 6.1 nM, protecting enkephalins from being broken down by these enzymes. (Racecadotril itself is much less potent at 4500 nM.)[7][8] This reduces diarrhea related hypersecretion in the small intestine without influencing basal secretion. Racecadotril also has no influence on the time substances, bacteria or virus particles stay in the intestine.[10]
Pharmacokinetics
Some metabolites of racecadotril. top left: precursor to the active metabolite top right: active metabolite bottom row: inactive metabolites
Racecadotril is rapidly absorbed after oral administration and reaches Cmax within 60 minutes. Food delays Cmax by 60 to 90 minutes but does not affect the overall bioavailability. Racecadotril is rapidly and effectively metabolized to the moderately active S-acetylthiorphan the main active metabolite thiorphan, of which 90% are bound to blood plasma proteins. In therapeutic doses, racecadotril does not pass the blood–brain barrier. Inhibition of enkephalinases starts 30 minutes after administration, reaches its maximum (75–90% inhibition with a therapeutic dose) two hours after administration, and lasts for eight hours. The elimination half-life, measured from enkephalinase inhibition, is three hours.[7][8][9]
Thiorphan is further metabolized to inactive metabolites such as the methyl thioether and the methyl sulfoxide. Both active and inactive metabolites are excreted, mostly via the kidney (81.4%), and to a lesser extent via the feces (8%).[10]
Society and culture
Brand names
In France, Portugal and Spain it is sold as Tiorfan and in Italy as Tiorfix. In India it is available as Redotril and Enuff.[4] In the Philippines it is sold as Hidrasec.
^ abBrayfield A, ed. (13 December 2013). "Racecadotril". Martindale: The Complete Drug Reference. London, UK: Pharmaceutical Press. Retrieved 6 May 2014.
^Spillantini MG, Geppetti P, Fanciullacci M, Michelacci S, Lecomte JM, Sicuteri F (June 1986). "In vivo 'enkephalinase' inhibition by acetorphan in human plasma and CSF". European Journal of Pharmacology. 125 (1): 147–150. doi:10.1016/0014-2999(86)90094-4. PMID3015640.
