Loperamide

Loperamide is an opioid-receptor agonist used mainly for its peripheral gastrointestinal effects. It reduces propulsive motility and has an antisecretory action, providing a symptomatic role in selected diarrheal disorders. Veterinary use is largely empirical and most often involves dogs. Transporter-mediated restriction of brain exposure contributes to its usual peripheral pharmacologic profile.

Group

Peripheral opioid antidiarrhoeal

Mechanism of Action

Loperamide activates mu-opioid receptors in the intestinal wall, reducing excitatory neurotransmitter release, propulsive contractions and secretory activity. Increased transit time and segmentation can enhance fluid and electrolyte absorption. P-glycoprotein normally limits central nervous system exposure, so the expected effect is predominantly intestinal. Longer intestinal residence and reduced secretion can produce firmer stools.

Dose Rates

Dogs

Use / stage	Dose	Route	Schedule	Instructions
Symptomatic diarrhoea	0.12 mg/kg	PO	Every 8–12 h	Do not use in: ABCB1-associated opioid sensitivity
Symptomatic diarrhoea	0.08 mg/kg	PO	Every 8 h	Up to 5 days; Do not use in: ABCB1-associated opioid sensitivity, Suspected invasive enteric infection; Short-term use; do not mask infection or ileus.
Symptomatic diarrhoea	0.1–0.2 mg/kg	PO	Every 8–12 h	Up to 5 days; Do not use in: ABCB1-associated opioid sensitivity, Suspected invasive enteric infection; Short-term use; do not mask infection or ileus.
Symptomatic diarrhoea	0.1 mg/kg	PO	Every 8 h	Up to 5 days; Do not use in: ABCB1-associated opioid sensitivity, Suspected invasive enteric infection; Short-term use; do not mask infection or ileus.
Symptomatic diarrhoea	0.08 mg/kg	PO	Every 6–8 h	Up to 5 days; Do not use in: ABCB1-associated opioid sensitivity, Suspected invasive enteric infection; Short-term use; do not mask infection or ileus.
Symptomatic diarrhoea	0.1–0.2 mg/kg	PO	Every 6–12 h	Up to 5 days; Do not use in: ABCB1-associated opioid sensitivity, Suspected invasive enteric infection; Short-term use; do not mask infection or ileus.
Chemotherapy-associated diarrhoea	0.08 mg/kg	PO	Every 8 h	Do not use in: ABCB1-associated opioid sensitivity

Cats

Use / stage	Dose	Route	Schedule	Instructions
Symptomatic diarrhoea	0.08–0.16 mg/kg	PO	Every 12 h
Symptomatic diarrhoea	0.04–0.06 mg/kg	PO	Every 12 h	Feline opioid antidiarrhoeal use is controversial; excitement may occur.

Rabbits

Use / stage	Dose	Route	Schedule	Instructions
Staged diarrhoea treatment	Reference only	PO		0.1 mg/kg every 8 hours for 3 days, then once daily for 2 days; the staged schedule must remain explicit. The described dose is delivered in 1 mL water.

Mice

Use / stage	Dose	Route	Schedule	Instructions
Staged diarrhoea treatment	Reference only	PO		0.1 mg/kg every 8 hours for 3 days, then once daily for 2 days; the staged schedule must remain explicit. The described dose is delivered in 1 mL water.

Rats

Use / stage	Dose	Route	Schedule	Instructions
Staged diarrhoea treatment	Reference only	PO		0.1 mg/kg every 8 hours for 3 days, then once daily for 2 days; the staged schedule must remain explicit. The described dose is delivered in 1 mL water.

Gerbils

Use / stage	Dose	Route	Schedule	Instructions
Staged diarrhoea treatment	Reference only	PO		0.1 mg/kg every 8 hours for 3 days, then once daily for 2 days; the staged schedule must remain explicit. The described dose is delivered in 1 mL water.

Hamsters

Use / stage	Dose	Route	Schedule	Instructions
Staged diarrhoea treatment	Reference only	PO		0.1 mg/kg every 8 hours for 3 days, then once daily for 2 days; the staged schedule must remain explicit. The described dose is delivered in 1 mL water.

Guinea pigs

Use / stage	Dose	Route	Schedule	Instructions
Staged diarrhoea treatment	Reference only	PO		0.1 mg/kg every 8 hours for 3 days, then once daily for 2 days; the staged schedule must remain explicit. The described dose is delivered in 1 mL water.

Chinchillas

Use / stage	Dose	Route	Schedule	Instructions
Staged diarrhoea treatment	Reference only	PO		0.1 mg/kg every 8 hours for 3 days, then once daily for 2 days; the staged schedule must remain explicit. The described dose is delivered in 1 mL water.

Indications

Short-term symptomatic treatment of selected acute nonspecific diarrhea in dogs, with limited controlled veterinary efficacy evidence.
Specialist symptomatic management of selected treatment-associated diarrhea in dogs, including some anticancer-drug-associated cases.

Contraindications

ABCB1-associated opioid sensitivity
Avoid when decreased intestinal motility would be harmful.
Suspected enteric infection, obstructive/acute abdominal disease or hepatic encephalopathy requires particular caution; central excitation can occur in cats.

Interactions

P-glycoprotein inhibitors such as ketoconazole can increase central nervous system penetration.

Adverse effects

Constipation and ileus
Profound sedation or central depression in susceptible dogs

Toxicity

Naloxone can reverse central opioid effects; support ventilation when needed and watch for recurrent toxicity.

Preparations

Preparation	Form	Strength	Route
Loperamide 2 mg tablet	Tablet	2 mg / tablet	PO
Loperamide 2 mg capsule	Capsule	2 mg / capsule	PO
Loperamide 0.2 mg/mL oral liquid	Oral Liquid	0.2 mg / mL	PO
Loperamide 1 mg/7.5 mL oral liquid	Oral Liquid	1 mg / 7.5 mL	PO

Monitoring and Administration

Assess the cause of diarrhoea and hydration. Avoid prolonged treatment.

Small dogs and collie-related breeds merit particular caution; do not infer safety from a usual peripheral mechanism.