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Lactulose for Dogs and Cats

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General drug information and indications

Lactulose is a non-digestible synthetic sugar which acts as a stool softener to treat chronic constipation in dogs and cats. Lactulose draws water into the intestine to soften the stool. It is particularly useful for the management of animals with chronic mega-colon.

Lactulose is also used in animals with liver disease to lower the blood ammonia levels. It is generally given orally two to four times a day. Your veterinarian may administer lactulose in an enema when an animal is being treated for severe liver failure.

Like many other drugs in veterinary medicine, this drug is not FDA approved for use in animals and is not available from a veterinary pharmaceutical manufacturer. Instead, it is compounded by a specialty pharmacy.

How to Give this Medication

Give this medication to your pet exactly as your veterinarian prescribes. If you miss giving your pet a dose of lactulose, give the next dose as soon as you remember or, if it is close to the next scheduled dose, return to the regular schedule. Do not double dose to catch up.

When using lactulose to manage chronic constipation, the treatment goal is 2-3 soft stools daily.

Cats frequently don't like the taste of this medication. You may need to work with your veterinarian to find a flavor that works best for your pet.

Wash your hands after giving your pet this medication.

Side Effects

Be sure to discuss any side effects with your veterinarian immediately.

The most common side effects in dogs and cats are digestive upset including diarrhea, excess gas and stomach cramping.


Keep this and all drugs out of reach of children. This drug should only be given to the animal for which it was prescribed. Do not give this medication to a person. Federal law restricts this drug to use by or on the order of a licensed veterinarian.

Lactulose should not be used with other laxatives. Because lactulose can cause diarrhea, it should be used carefully in animals that might be dehydrated or have electrolyte imbalances.

Lactulose may change the insulin requirements in a diabetic animal. Your veterinarian may choose to perform additional glucose monitoring.

Drug Interactions

Be sure to review with your veterinarian any medications or supplements your pet may be receiving.

Oral antacids and some oral antibiotics may decrease the effects of lactulose.


If you suspect your pet or another animal was accidentally overdosed or has eaten this medication inadvertently, contact your veterinarian or the A.S.P.C.A.'s Animal Poison Control Center at 888.426.4435. Always bring the prescription container with you when you take your pet for treatment.

If you or someone else has accidentally ingested this medication call the National Capital Poison Center at 800.222.1222.


Different strengths or dosage forms of lactulose may have different storage requirements. Read the labeling or ask your pharmacist for the storage requirements of the prescription you receive.

Dosage Forms Available from Wedgewood Pharmacy for Companion Animals

Learn more about the dosage forms available from Wedgewood Pharmacy

About the Author

Dr. Barbara Forney

Dr. Barbara Forney is a veterinary practitioner in Chester County, Pennsylvania. She has a master's degree in animal science from the University of Delaware and graduated from the University of Pennsylvania School of Veterinary Medicine in 1982.

She began to develop her interest in client education and medical writing in 1997. Recent publications include portions of The Pill Book Guide to Medication for Your Dog and Cat, and most recently Understanding Equine Medications published by the Bloodhorse.

Dr. Forney is an FEI veterinarian and an active member of the AAEP, AVMA, and AMWA.