Loperamide and Racecadotril

Mechanism

🚫 Loperamide

• Class: Intestinal peripheral μ-opioid receptor agonist.
• CNS effects: It is actively expelled from the blood-brain barrier by the efflux pump P-glycoprotein (P-gp) in normal doses.
• Does not exert central analgesic or addictive effects.

💧 Racecadotril

• Class: Selective inhibitor of the enzyme enolase/enrokephalin (Enkephalin peptidase).
• Mechanism: Selectively prolongs the half-life of endogenous enkephalins in the intestinal mucosa, reducing massive water secretion induced by toxins or inflammation.

Mechanism of action

Loperamide: It selectively binds to µ-type opioid receptors located on myenteric neurons of the gastrointestinal tract. Its activation drastically reduces intestinal peristalsis by inhibiting the release of acetylcholine and prostaglandins.

This molecular change prolongs gastrointestinal transit time, increases the absorption of fluids and electrolytes in enterocytes, and increases the basal tone of the internal anal sphincter in a coordinated manner.

Racecadotril: It is a prodrug hydrolyzed to its active metabolite, thiorphan. This is a highly selective and potent inhibitor of enkephalinase (neutral endopeptidase located in the membrane of epithelial cells of the small intestine).

Antisecretory Mechanism of Racecadotril

Endogenous neurotransmitter enkephalins act on mucosal δ-opioid receptors to inhibit gastric and colonic epithelial adenylate cyclase. By blocking enkephalinase, racecadotril prevents the physiological degradation of these enkephalins, thereby reducing excessive intracellular cAMP production induced by pathogens (such as cholera toxin or rotavirus) or inflammatory hormones. A selective reduction of the hypersecretion of water and chlorides towards the lumen is achieved without affecting in any way basal intestinal motility, reducing the duration of diarrhea without inducing secondary constipation.

Indicators and dose

Approved indications

• Loperamide: Symptomatic treatment of acute nonspecific diarrhea and chronic diarrhea in adults associated with inflammatory disease or intestinal resection.
• Racecadotril: Adjunctive treatment of acute diarrhea in infants (over 3 months of age), children and adults in combination with oral rehydration therapy.

Dosage and Clinical Adjustment

Loperamide (Adults):

• Acute diarrhea: Initial dose of 4 mg orally, followed by 2 mg after each subsequent liquid or semi-liquid stool. Do not exceed the dose of 16 mg per day. Discontinue treatment if there is no clinical improvement after 48 hours of continuous use.

Racecadotril:

• Adults: 100 mg orally three times a day in hard capsules, administered before main meals.
• Pediatrics (Infants over 3 months): Dosage adjusted by strict body weight: 9 kg: 10 mg three times a day; 9 - 13 kg: 20 mg three times a day; 13 - 27 kg: 30 mg three times a day. Administer dissolved in bottles or semi-solid foods.

Adjustment in Renal/Hepatic Failure: No large-scale clinical studies of racecadotril have been performed in these groups; caution is advised. No adjustment is required for loperamide.

Security

Contraindications

• Loperamide (Absolutes): Acute invasive diarrhea characterized by the presence of blood in feces (dysentery) and high fever (can prolong the contact of enteropathogens such as Salmonella, Shigella, Campylobacter with the mucosa). Pseudomembranous colitis associated with antibiotics. Severe acute ulcerative colitis (high risk of triggering toxic megacolon due to loss of motility). Contraindicated in children under 2 years of age due to the danger of fatal paralytic ileus.
• Racecadotril (Absolutes): Presence of marked invasive dysentery. Diarrhea associated with broad-spectrum antibiotics.

Adverse effects (ADRs)

• Loperamide: Noticeable rebound constipation, mild drowsiness, dizziness, xerostomia. QT prolongation and fatal ventricular arrhythmias only in cases of chronic abuse or massive intentional overdose (used as a recreational substitute for systemic opioids).
• Racecadotril: Occasional mild headache, vomiting, rare skin rashes or peripheral angioedema.

Safety for Use in Pregnancy

Loperamide: Category C. Its routine use during pregnancy is not recommended. It is compatible with breastfeeding as it is excreted in insignificant quantities.

Racecadotril: Its use is not recommended during pregnancy or during breastfeeding due to the lack of epidemiological safety data in humans.