Loperamide HCl

What is this medication for?

• Symptomatic treatment of non-infectious diarrhea; adjunct for chemotherapy-induced diarrhea (e.g., toceranib)
• Controversial — many clinicians avoid (excitatory reactions)

How is it given?

Give exactly as your veterinarian prescribed — never change the dose or stop on your own unless your veterinarian has told you to.

• Symptomatic therapy only — never masks infectious diarrhea or toxic ingestion without addressing the cause.

What if I miss a dose?

• Give it as soon as you remember — unless it is almost time for the next dose (then skip the missed one; never double up).
• Call your clinic if you miss more than one dose in a row.

Side effects — what should I watch for?

Effects listed as common in this handout

• CNS depression at 0.06 mg/kg in MDR1-mutant dogs (Documented (APCC))
• Excitatory behavior (Reason for feline controversy)

Worth a phone call to your veterinarian

• Paralytic ileus, toxic megacolon, pancreatitis (Potential/serious)

⚠️ Contact your veterinarian or an emergency clinic IMMEDIATELY if you notice

• Constipation, bloat, drowsiness (Usual-dose effects)

Before starting (or refilling), tell your veterinarian if your pet:

• has or has had: ABCB1-1Δ (MDR1) mutant dogs; untested "white-feet" herding breeds (Collies, Shelties, Aussies); diarrhea from toxic ingestion until toxin cleared; narcotic hypersensitivity
• has or has had: Acute abdominal conditions (masks diagnosis), head trauma/↑ICP, respiratory disease, hepatic disease with encephalopathy (hepatic coma risk), hypothyroidism, Addison's, severe renal insufficiency, geriatric/debilitated; suspected enteric infections

• is pregnant, nursing, or used for breeding
• is taking any other medications, supplements, or flea/tick products, including:
  • P-gp inhibitors (amiodarone, carvedilol, erythromycin, ketoconazole, itraconazole)
  • Other CNS/respiratory depressants

Storage and handling

Room temperature. OTC capsules/tablets 2 mg; liquid 0.2 mg/mL for small-patient titration.

Good to know

• The MDR1/ivermectin-sensitivity connection is the exam pearl: the same P-glycoprotein mutation that causes ivermectin toxicity in Collies lets loperamide into the brain — check "white-feet" breeds before recommending an OTC antidiarrheal.
• Naloxone reverses severe loperamide depression (higher doses may be needed); avoid apomorphine for emesis induction in overdose (additive CNS depression).
• Symptomatic therapy only — never masks infectious diarrhea or toxic ingestion without addressing the cause.
• Cats: use only with deliberate caution and clear rationale; excitatory reactions are the documented concern.