What are the recommended lactulose doses for adults with hepatic encephalopathy, for adult constipation, and for children older than two years?

Lactulose Dosing Guidelines

For Hepatic Encephalopathy in Adults

For acute hepatic encephalopathy, initiate lactulose at 30-45 mL (20-30 g) every 1-2 hours until the patient produces at least 2 soft bowel movements per day, then titrate to a maintenance dose of 30-45 mL three to four times daily to maintain 2-3 soft stools daily. 1, 2

Acute Phase Dosing

• Start with 25-30 mL of lactulose syrup every 1-2 hours orally until achieving at least 2 soft or loose bowel movements per day 1
• The FDA-approved regimen specifies hourly doses of 30-45 mL to induce rapid laxation in the initial phase 2
• Clinical improvement may occur within 24 hours but can take up to 48 hours or longer 2

Maintenance Phase Dosing

• Once initial response is achieved, reduce to 30-45 mL (20-30 g) administered 3-4 times daily 3, 2
• The therapeutic goal is maintaining 2-3 soft stools per day, not exceeding this target 1, 3
• Continuous long-term therapy is indicated to prevent recurrence of hepatic encephalopathy 2

Rectal Administration (When Oral Route Contraindicated)

• For patients in impending coma, coma stage, or when aspiration risk exists, administer 300 mL lactulose mixed with 700 mL water or physiologic saline as a retention enema 4, 2
• Retain the solution for 30-60 minutes 4, 2
• Repeat every 4-6 hours as needed 2
• This approach delivers up to 1,200 mL (800 g) of lactulose daily when given 4 times daily 3

Critical Safety Warnings

It is a dangerous misconception that lack of effect from smaller doses should be remedied by much larger doses—overuse can cause aspiration, dehydration, hypernatremia, severe perianal skin irritation, and paradoxically precipitate hepatic encephalopathy. 1, 3

• Do not escalate doses beyond what produces 2-3 soft stools daily 1, 3
• If no response occurs after appropriate dosing, investigate precipitating factors (infection, GI bleeding, constipation, medications) rather than escalating lactulose indefinitely 3
• Monitor for perianal skin breakdown with chronic use 3

For Constipation in Adults

For chronic idiopathic constipation, start with 15-30 mL (10-20 g) daily and may increase to a maximum of 60 mL (40 g) daily if needed. 3, 2

Initial Dosing

• Begin with 15-30 mL (10-20 g or 1-2 packets) daily 3
• The usual adult oral dosage is 2-3 tablespoonfuls (30-45 mL) three or four times daily 2

Maximum Dosing

• The FDA-approved maximum dose for constipation is 40 g (60 mL or 2-4 packets) daily 3
• Adjust dosage every day or two to produce 2-3 soft stools daily 2

Common Side Effects

• Bloating and flatulence are dose-dependent and may limit use 3
• If diarrhea occurs, reduce dose immediately 2

For Children Older Than Two Years

For infants, the recommended initial daily oral dose is 2.5-10 mL in divided doses; for older children and adolescents, the total daily dose is 40-90 mL. 2

Pediatric Dosing Considerations

• Very little information exists on lactulose use in young children and adolescents 2
• The therapeutic goal remains producing 2-3 soft stools daily, same as adults 2
• If initial dose causes diarrhea, reduce immediately 2
• If diarrhea persists despite dose reduction, discontinue lactulose 2

Age-Specific Ranges

• Infants: 2.5-10 mL daily in divided doses 2
• Older children and adolescents: 40-90 mL total daily dose 2