|Systematic (IUPAC) name|
|Legal status||OTC (CA) GSL (UK) OTC (US)|
|Bioavailability||Not significantly absorbed from the gut|
|Half-life||9.1 to 14.4 hours (average 10.8 hours)|
34552-83-5 (with HCl)
|Mol. mass||477.037 g/mol (513.506 with HCl)|
| (what is this?)
Loperamide (pron.: //), a piperidine derivative, is an opioid drug used against diarrhea resulting from gastroenteritis or inflammatory bowel disease. In most countries it is available generically and under brand names such as Lopex, Imodium, Dimor, Fortasec, Lopedium, and Pepto Diarrhea Control. It was developed at Janssen Pharmaceutica.
Medical uses 
Mechanism of action 
Like morphine, it works by decreasing the activity of the myenteric plexus, which decreases the tone of the longitudinal smooth muscles but increases the tone of circular smooth muscles of the intestinal wall. This increases the amount of time substances stay in the intestine, allowing for more water to be absorbed out of the fecal matter. Loperamide also decreases colonic mass movements and suppresses the gastrocolic reflex.
Crossing the blood–brain barrier 
Concurrent administration of P-glycoprotein inhibitors such as quinidine and its other isomer quinine (although much higher doses must be used), PPIs like omeprazole (Prilosec OTC) and even black pepper (piperine as the active ingredient) could potentially allow loperamide to cross the blood–brain barrier. It should however be noted that only quinidine with loperamide was found to produce respiratory depression, indicative of central opioid action.
Many physicians and pharmacists believe that loperamide does not cross the blood–brain barrier. In fact, however, loperamide does cross this barrier, although it is immediately pumped back out into non–central nervous system (CNS) circulation by P-glycoprotein. While this mechanism effectively shields the CNS from exposure (and thus risk of CNS tolerance/dependence) to loperamide, many drugs are known to inhibit P-glycoprotein and may thus render the CNS vulnerable to opiate agonism by loperamide.
However, loperamide has been shown to cause a mild physical dependence during preclinical studies, specifically in mice, rats, and rhesus monkeys. Symptoms of mild opiate withdrawal have been observed following abrupt discontinuation of long-term therapy with loperamide.
The use of loperamide (Imodium) in children under 2 years is not recommended. There have been rare reports of fatal paralytic ileus associated with abdominal distention. Most of these reports occurred in the setting of acute dysentery, overdose, and with very young children less than two years of age. In 1990, all pediatric formulations of the antidiarrheal loperamide (Imodium and others) were banned in Pakistan.
Treatment should be avoided in the presence of high fever or if the stool is bloody (dysentery). It is of no value in diarrhea caused by cholera, Shigella or Campylobacter. Treatment is not recommended for patients that could suffer detrimental effects from rebound constipation. If there is a suspicion of diarrhea associated with organisms that can penetrate the intestinal walls, such as E. coli O157:H7 or salmonella, loperamide is contraindicated.
Adverse effects 
Adverse drug reactions (ADRs) associated with loperamide include abdominal pain and bloating, nausea, vomiting and constipation. Rare side-effects associated with loperamide are paralytic ileus, dizziness and rashes.
See also 
- Dextromethorphan - another opioid medication prescribed for non-analgesic purposes
- Methylnaltrexone - a Mu opioid antagonist (in contrast to the Mu opioid agonist loperamide) that does not cross the blood brain barrier so as to not affect CNS
- Simethicone - an anti-gas frequently combined with loperamide in medications
- Traveler's diarrhea
- Active carbon
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