Antimotility Drug

Loperamide

A peripherally acting opioid agonist that slows the gut, used for acute and chronic diarrhea and high ileostomy output.

Drug card

Class: Antimotility drug
How it works: Activating gut mu-opioid receptors to slow peristalsis
Used for: Acute diarrhea, and chronic diarrhea in bowel disease
Reducing output from an ileostomy
Known for: Constipation
QT prolongation, torsades and cardiac arrest at high doses

Study it as a flashcard, and it comes back before you forget it.

Mechanism of action

How does loperamide work?

Binds mu-opioid receptors in the gut wall, cutting acetylcholine and prostaglandin release, so peristalsis slows, transit time lengthens, stools firm up and anal sphincter tone rises. It is a P-glycoprotein substrate with few central effects at normal doses; very high doses, or P-glycoprotein and CYP3A4 or CYP2C8 inhibitors, raise its central and cardiac effects.

Uses

What is loperamide used for?

Acute diarrhea, and chronic diarrhea in bowel disease
Reducing output from an ileostomy

Side effects

Side effects of loperamide

ConstipationKnown for
QT prolongation, torsades and cardiac arrest at high dosesKnown forSerious
Abdominal cramps and bloating
Nausea
Dizziness
Drowsiness and tiredness
Paralytic ileus and toxic megacolonSerious
Breathing depression in children under 2Serious
Urinary retention
Severe skin reactions (such as SJS/TEN)Serious
AnaphylaxisSerious

Known for marks what an exam expects you to know it for.

Watch for

Cautions and what sets it apart

Doses above the recommended maximum, often taken for opioid withdrawal, have caused torsades and cardiac arrest.
Avoid with QT-prolonging drugs and with inhibitors of CYP3A4, CYP2C8 or P-glycoprotein such as itraconazole and gemfibrozil.
Contraindicated under 2 years, in dysentery, bacterial enterocolitis, C. difficile colitis and acute ulcerative colitis.

Good to know: Misused in very large doses to ease opioid withdrawal or for a mild high; such doses have caused fatal heart rhythms.

Remember it

A way to remember it

An opioid that stays in the gut.

Loperamide acts on mu-opioid receptors in the gut wall and has few central effects at normal doses, so its main effect is a slower bowel; constipation is the usual side effect, and huge doses can cause dangerous heart rhythms.

Written for biofideX

Its class

Antimotility drugs

Antimotility drugs are opioid agonists that act on mu-opioid receptors in the wall of the gut. They reduce the release of acetylcholine and prostaglandins there, which damps propulsive peristalsis, so gut contents move more slowly and more water and salt are absorbed. They also tighten the anal sphincter, easing urgency. They treat the symptom, not the cause of the diarrhea.

Easily mixed up with antimuscarinics and stimulant laxatives.

Sources

Checked against

Written for biofideX in plain words, after checking these references:

For learning pharmacology, not for treatment decisions: no doses are given, and a prescriber, pharmacist or the product's own label is the word on any one patient. Spotted a mistake? Tell us and we'll correct it.

Practice it

Stomach and gut

Loperamide is one of 15 drugs practiced together here: their classes, how they work, what they treat and what they're known for.

Start Practicing

Or browse every drug card