Lactulose

About Lactulose

Lactulose is poorly absorbed, so it reaches the colon virtually unchanged. There, bacteria break it down, mainly to lactic acid, which raises the water content of the stool and softens it; the acid conditions also trap ammonia in the colon as ammonium, which the laxative effect carries out, lowering blood ammonia. For constipation the usual adult dose is 15 to 30 mL (10 to 20 g) of solution a day, up to 60 mL, or 10 to 20 g a day from packets, up to 40 g; a normal bowel movement can take 24 to 48 hours. For hepatic encephalopathy, adults usually take 30 to 45 mL three or four times a day, adjusted every day or two to produce two or three soft stools a day; treatment may start with hourly doses, or with a retention enema for someone in or near a coma, and long-term use helps prevent recurrence.

There is no boxed warning. Lactulose contains some galactose and lactose, so it is not for anyone on a low-galactose diet and is used with caution in diabetes. Gas, bloating, belching and cramps are common, especially at first, and nausea and vomiting can occur; too high a dose causes diarrhea, which can lead to loss of fluid, low potassium and high sodium. The constipation labels call for periodic electrolyte checks in older, frail patients who take it for more than six months, and say safety and effectiveness in children have not been established. Because hydrogen gas from the colon is a theoretical hazard during electrocautery at colonoscopy, the bowel is first cleansed with a non-fermentable solution.

The solution comes in one strength, 10 g per 15 mL, but each product’s label names its use: some are labeled for constipation, others, including Enulose and Generlac, for hepatic encephalopathy. Those labels give doses for infants and older children, warn that infants can develop low sodium and dehydration, and advise against other laxatives, especially at the start, because their loose stools can make the lactulose dose look adequate. Constulose, a constipation product, has been discontinued. Single-dose packets of crystals, dissolved in half a glass (4 ounces) of water, are labeled for constipation; they have been sold as Kristalose and, since September 2025, as Lactulose Crystalline, both made under the same FDA approval.

Taking Lactulose

How to take it

Exactly as prescribed: usually once a day for constipation and three or four times a day for liver disease. To improve the taste, MedlinePlus suggests mixing the dose with half a glass of water, milk or fruit juice. Dissolve a packet in half a glass (4 ounces) of water.

If you miss a dose

Take it as soon as you remember, unless it is almost time for the next dose; then skip the missed dose. Do not take a double dose to make up for a missed one.

Storage

At room temperature, tightly closed, out of reach of children; do not freeze. The solution may darken normally, but do not use it if it turns very dark or cloudy; freezing can thicken it until it will not pour, and it returns to normal at room temperature. Use a take-back program rather than flushing it.

Interactions to know about

Antacids that are not absorbed can blunt its effect in the colon. For hepatic encephalopathy, other laxatives are avoided, especially at first, and anyone also taking an oral antibiotic such as neomycin is watched closely.

This summarizes the official prescribing information. Your prescriber’s and pharmacist’s instructions, and the leaflet that comes with your medicine, take priority.

Why the cash price for Lactulose differs from pharmacy to pharmacy

Lactulose solution is an old generic from several companies and costs pharmacies little, so a quote depends mostly on volume: a constipation dose lasts a while in one bottle, while encephalopathy doses can use a pint every few days. Unit-dose cups are a separate package from bottles, with their own price.

Packets are a separate product, made under one FDA approval for both Kristalose and Lactulose Crystalline, and a pharmacy may need to order them. Solution and packets are different dosage forms, so one cannot be switched for the other without the prescriber’s approval.

Ways to pay less for Lactulose without insurance

• Ask for generic lactulose solution, and ask whether it is on the pharmacy’s flat-price generic list.
• Ask the prescriber to write a quantity that matches a full bottle size, such as a pint or a quart, and once the dose is settled, ask for a ninety-day supply.
• If packets are prescribed and quotes are high, ask the prescriber whether the solution would suit you.
• Compare more than one pharmacy, since quotes for the same volume can differ.
• Upload the prescription to Script Unlock so licensed pharmacies can quote their cash price. You pay the pharmacy directly.

Questions to ask your pharmacist about Lactulose

1. 1.How many milliliters is my dose, and how should I measure it?
2. 2.How many bowel movements a day should I aim for, and when should I call about diarrhea?
3. 3.Is it safe with my diabetes?
4. 4.Can I take it with my antacid or my antibiotic?

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