Lactulose

What is this medication for?

• Hepatic encephalopathy (prevention + treatment — trap ammonia as NH4+ in colon)
• Constipation (osmotic laxative; megacolon adjunct)

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.

• In feline megacolon: pairs with cisapride (prokinetic) + fiber; lactulose handles the stool texture, cisapride the motility.

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

• Flatulence, cramping, gastric distention (Common early, abates with time)
• Diarrhea + dehydration (= overdosage — reduce dose)
• Altered insulin requirement (Syrup contains free lactose/galactose)

Worth a phone call to your veterinarian

• Any new symptom that worries you.

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

• Trouble breathing, collapse, seizures, severe vomiting or diarrhea, facial swelling, or pale gums

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

• has or has had: Galactosemia (human)
• has or has had: Preexisting fluid/electrolyte imbalance (diarrhea worsens); diabetes mellitus

• is pregnant, nursing, or used for breeding
• is taking any other medications, supplements, or flea/tick products, including:
  • Oral antibiotics (neomycin)
  • Antacids (aluminum)

Storage and handling

Room temperature; avoid freezing. Syrup (10 g/15 mL) or crystals for solution.

Good to know

• The dose IS the stool: titrate to 2–3 soft stools per day — this is the exam answer and the practical rule.
• Dual mechanism in hepatic encephalopathy: osmotic catharsis + acidifying the colon so NH3 diffuses out of blood and is trapped as NH4+ (ionized, non-absorbable) in feces.
• Cats hate the syrup — Kristalose crystals in food or the enema route (HE crisis) solve compliance.
• In feline megacolon: pairs with cisapride (prokinetic) + fiber; lactulose handles the stool texture, cisapride the motility.