What is the recommended dosing for lactulose (lactulose)?

Lactulose Dosing Recommendations

The FDA-approved dosing for lactulose in constipation is 30-45 mL (20-30 grams) three to four times daily, adjusted every 1-2 days to produce 2-3 soft stools daily. 1

Dosing by Indication

For Constipation:

• Initial dose: 30-45 mL (20-30 grams) orally 3-4 times daily 1
• Maintenance dose: Adjust every 1-2 days to achieve 2-3 soft bowel movements daily 1
• Alternative dosing: Some evidence supports once-daily dosing of 20g in the evening, which showed similar efficacy to twice-daily dosing 2

For Hepatic Encephalopathy:

• Initial/acute treatment: 30-45 mL every 1-2 hours until at least two soft bowel movements occur 3, 1
• Maintenance dose: 30-45 mL orally every 6-8 hours, titrated to maintain 2-3 soft bowel movements daily 3
• Rectal administration (for comatose patients): 300 mL lactulose mixed with 700 mL water or saline as retention enema for 30-60 minutes, repeatable every 4-6 hours 1

For Pediatric Patients:

• Infants: 2.5-10 mL daily in divided doses 1
• Older children and adolescents: 40-90 mL total daily dose 1

Dosing Considerations

Efficacy Factors:

• Lactulose works by exerting an osmotic laxative effect in the colon to promote peristalsis 4
• Clinical response may take 24-48 hours or longer to manifest 1
• In elderly patients, lactulose significantly increases bowel movement frequency compared to placebo (p<0.02) 5
• Lactulose reduces fecal impactions and need for enemas in elderly patients 4, 5

Dose Adjustment:

• If diarrhea occurs, particularly in pediatric patients, reduce the dose immediately 1
• If no defecation occurs for more than 48 hours, consider doubling the dose 4
• Once laxative effect is achieved in hepatic encephalopathy, reduce to maintenance dose 1

Side Effects and Precautions

Common Side Effects:

• Bloating and flatulence (dose-dependent) are very common and may limit use 4, 3
• Abdominal cramping may occur, especially at higher doses 4

Important Precautions:

• Overdosing can cause dehydration, hypernatremia, and paradoxically precipitate hepatic encephalopathy 3
• Avoid cleansing enemas containing soap suds or alkaline agents when using rectal lactulose 1
• For diabetic patients with mild constipation, lactulose may not significantly increase blood sugar levels 4

Practical Administration Tips

• For constipation resistant to initial therapy, lactulose can be increased up to 40g (60 mL) daily 4
• In hepatic encephalopathy, continuous long-term therapy is indicated to prevent recurrence 1
• For elderly patients, lactulose has shown superior efficacy compared to glucose in relieving constipation symptoms 5
• When transitioning from rectal to oral administration in hepatic encephalopathy, start oral dosing before completely stopping rectal administration 1

Lactulose remains a valuable option for chronic idiopathic constipation when over-the-counter therapies fail, despite the very low certainty of evidence supporting its use 4. For hepatic encephalopathy, it is considered first-line therapy with stronger evidence supporting its use 3.