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Lactulose

Osmotic laxative / Hepatic encephalopathy treatment
Last reviewed 19 Apr 2026 · PetCare.AI Editorial Team
Species
Dog, Cat
Brands
3 available
Interactions
1 documented
Formulations
1

Mechanism of action

Synthetic disaccharide metabolized by colonic bacteria to organic acids, creating osmotic gradient drawing water into the colon; also traps ammonia in the gut lumen as ammonium

At a glance

Class
Osmotic laxative / Hepatic encephalopathy treatment
Schedule
OTC
Storage
Store below 25°C, do not freeze

Dosing

🐕

Dog

Constipation
Dose
0.5–1 mL/kg
Route
PO
Frequency
BID to TID
Max dose
30 mL/dose; 90 mL/day
Duration: Adjust to effect (soft formed stool)
Hepatic encephalopathy
Dose
0.5–1 mL/kg
Route
PO, Rectal (retention enema)
Frequency
TID to QID
Max dose
30 mL/dose; 120 mL/day
Duration: Ongoing; titrate to 2–3 soft stools/day
🐈

Cat

Constipation / Megacolon
Dose
0.5–1 mL/kg
Route
PO
Frequency
BID to TID
Max dose
5 mL/dose; 15 mL/day
Duration: Adjust to effect
Hepatic encephalopathy
Dose
0.5–1 mL/kg
Route
PO
Frequency
BID to TID
Max dose
5 mL/dose; 15 mL/day
Duration: Ongoing

Formulations

🧴

Oral solution — 1

Strength
10g/15mL (66.7%)
Available in India

Storage

Store below 25°C, do not freeze

Safety

Absolute contraindications — do not use

  • GI obstruction

Use with caution

  • Diabetes mellitus
    Contains galactose and lactose; minimal absorption but monitor

Adverse effects

Common
Flatulence
Abdominal cramping
Diarrhoea (over-dosing)
Serious
Dehydration and electrolyte imbalances (excessive dosing)

Monitoring parameters

Stool frequency and consistencyAmmonia levels (hepatic encephalopathy)Hydration status

Interactions

Moderate — 1

Neomycin
moderate
Both used for hepatic encephalopathy (lactulose: acidifies colon trapping NH3; neomycin: kills ammonia-producing bacteria). Neomycin may also kill bacteria that ferment lactulose to lactic acid, potentially reducing lactulose efficacy.
Management: Combination is clinically used but evidence of antagonism exists. Monitor ammonia levels and clinical response. Some clinicians avoid combining.

Brands

International

Duphalac
Abbott

India

Looz
Sun Pharma
Laxose
Cipla

FAQs

Frequently asked questions

›What is Lactulose?
Lactulose is a osmotic laxative / hepatic encephalopathy treatment used in pets. Synthetic disaccharide metabolized by colonic bacteria to organic acids, creating osmotic gradient drawing water into the colon; also traps ammonia in the gut lumen as ammonium
›What is Lactulose used for in pets?
Lactulose is used in veterinary medicine for: Constipation; Hepatic encephalopathy; Constipation / Megacolon.
›What is the Lactulose dose for dogs?
For dogs, Lactulose is typically dosed as follows — Constipation: 0.5–1 mL/kg PO BID to TID; Hepatic encephalopathy: 0.5–1 mL/kg PO/Rectal (retention enema) TID to QID. Always consult your veterinarian for a dose tailored to your pet's weight, age, and condition.
›What is the Lactulose dose for cats?
For cats, Lactulose is typically dosed as follows — Constipation / Megacolon: 0.5–1 mL/kg PO BID to TID; Hepatic encephalopathy: 0.5–1 mL/kg PO BID to TID. Always consult your veterinarian for a dose tailored to your pet's weight, age, and condition.
›What are the side effects of Lactulose?
Common: Flatulence, Abdominal cramping, Diarrhoea (over-dosing). Serious (call your vet immediately): Dehydration and electrolyte imbalances (excessive dosing).
›Does Lactulose need a prescription?
Lactulose is available over the counter. Even so, you should consult your veterinarian before giving any medication to your pet.
›When should Lactulose not be used?
Do not use Lactulose if: GI obstruction.

References

References

Textbooks & handbooks

  • Plumb, D.C. Plumb's Veterinary Drug Handbook. 10th ed., Wiley-Blackwell, 2023.
  • Vail, D.M., Thamm, D.H., & Liptak, J.M. (eds.). Withrow & MacEwen's Small Animal Clinical Oncology. 6th ed., Saunders/Elsevier, 2020.
  • Riviere, J.E., & Papich, M.G. (eds.). Veterinary Pharmacology and Therapeutics. 10th ed., Wiley-Blackwell, 2018.
  • National Research Council. Nutrient Requirements of Dogs and Cats. National Academies Press, Washington DC, 2006.
  • The Merck Veterinary Manual. Merck & Co., Online edition. https://www.merckvetmanual.com/

Clinical guidelines & consensus

  • Fletcher, D.J., Boller, M., Brainard, B.M., et al. "RECOVER Evidence and Knowledge Gap Analysis on Veterinary CPR." Journal of Veterinary Emergency and Critical Care, 2012;22(S1):S102–S131.
  • American Animal Hospital Association. 2018 AAHA Diabetes Management Guidelines for Dogs and Cats. AAHA Press.

Journals & peer-reviewed studies

  • Hogan, D.F., Fox, P.R., Jacob, K., et al. "Secondary prevention of cardiogenic arterial thromboembolism in the cat: The FAT CAT study." Journal of Veterinary Cardiology, 2015;17(Suppl 1):S306–S317.
  • Boswood, A., Häggström, J., Gordon, S.G., et al. "Effect of Pimobendan in Dogs with Preclinical Myxomatous Mitral Valve Disease and Cardiomegaly: The EPIC Study — A Randomized Clinical Trial." Journal of Veterinary Internal Medicine, 2016;30(6):1765–1779.
  • ASPCA Animal Poison Control Center. Toxicology and Poison Management Guidelines. American Society for the Prevention of Cruelty to Animals. https://www.aspca.org/pet-care/animal-poison-control

Regulatory & approvals

  • Central Drugs Standard Control Organisation (CDSCO), Government of India. Veterinary Drug Approval Registry, 1969–2026. Directorate General of Health Services. https://cdsco.gov.in/

Databases

  • Washington State University, College of Veterinary Medicine. Veterinary Clinical Pharmacology Laboratory (VCPL) — MDR1 Multidrug Sensitivity Database. https://vcpl.vetmed.wsu.edu/
Educational reference only
This information is provided for educational purposes and is not a substitute for professional veterinary advice, diagnosis, or treatment. Always consult a qualified veterinarian before administering any medication to your pet. Find a vet near you →