Diphenoxylate hydrochloride

Diphenoxylate Hydrochloride (Lomotil, Lonox, Lomanate)

(for veterinary information only)

Brand Name: Lomotil, Lonox, Lomanate

Available in 2.5 mg tablets or as oral liquid


Intestinal motility refers to the ability of intestinal muscle to contract and move intestinal contents from the mouth end of the animal to the anal end.

Years ago it was thought that diarrhea was the result of excessive motility in the intestinal tract, that intestinal contents were rushed through prematurely in a sequence of muscular spasms. For years, diarrhea was symptomatically treated with medications designed to abolish intestinal muscle tone with the idea that these spasms could be prevented.  Results were disappointing.

More recently, the details of intestinal contractions have been elucidated.  There are many types of muscle contractions in the intestine. There is the forward-propelling peristaltic contraction that moves intestinal contents forward. There is the segmental contraction that can divide the intestine into small segments where different materials can be sequestered temporarily for absorption and digestion. There is also an overall general muscle tone or tonus to the intestinal tract and it is this tonus that controls the speed by which intestinal contents move.  More muscle tone/tonus means slower movement of intestinal contents, more absorption of water from the intestinal contents, and less tendency towards diarrhea. When this muscle tone is abolished, intestinal contents simply pour through the tract and diarrhea is worse.

How this Medication Works

Despite its inability to produce recreational euphoria, diphenoxylate hydrochloride is actually a member of the opiate class of drugs.  (A small amount of atropine is added to diphenoxylate to discourage abuse for recreational purposes; at recommended doses, the atropine causes no effects but if one tries to use larger quantities, the atropine produces unpleasant symptoms.)  Opiates have numerous effects that have made them beneficial - as well targets of abuse -  for centuries; one such beneficial effect is an increase in general muscle tone of the small intestine. As described above, increasing tonus means more absorption of water and nutrients and less diarrhea.

Loperamide is a similar drug and may be preferable for dogs as it is believed to have a faster onset of action and lasts longer. Definitive studies are lacking.

Side Effects

Side effects are not common with diphenoxylate hydrochloride but constipation and/or bloating are possibilities. Since diphenoxylate hydrochloride is an opiate, tranquilization is a possible side effect.

Interactions with other Drugs

Opiates should not be given to patients concurrently taking L-Deprenyl (Anipryl) or other monoamine oxidase inhibitors.  Actually serious reactions have only been observed between L-Deprenyl and meperidine (Demerol) but to be safe the warning has been extended to all opiates.

Tranquilizers and antihistamines should not be used with opiates as sedating properties may be overly enhanced.

Concerns and Cautions

Use of this medication may falsely elevate lab tests for pancreatitis (amylase and lipase levels).

Diphenoxylate hydrochloride should be stored at room temperature in light resistant containers.

This medication is contraindicated for diarrhea involving intestinal toxins parvovirus enteritis or patients with liver failure are good examples).  In these cases, the absorption enhancing effects of diphenoxylate hydrochloride could be a serious problem as one would not want to enhance the absorption of intestinal toxins.

Diphenoxylate hydrochloride should not be used in debilitated patients. Caution is recommended for patients with Addison's disease, increased intracranial pressures, hypothyroidism, liver disease, or severe kidney failure.

It is our policy not to give dosing information over the Internet.


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