What is the proper administration and dosing of lactulose (osmotic laxative)?

How to Give Lactulose

For constipation, start lactulose at 15-30 mL (10-20 g) once daily in the evening, titrating every few days to achieve 2-3 soft bowel movements per day, with a maximum dose of 60 mL (40 g) daily. 1, 2

Route of Administration

Oral Administration (First-Line)

• Administer 15-30 mL (10-20 g) orally once daily, preferably in the evening to optimize compliance and minimize dose-dependent gastrointestinal side effects 1, 3
• If patients cannot take medications orally, administer via nasogastric tube 4
• The dose may be adjusted every day or two to produce 2-3 soft stools daily 2

Rectal Administration (Severe Cases Only)

• For severe hepatic encephalopathy (West-Haven grade 3 or higher) when oral/NG routes are not feasible, mix 300 mL lactulose with 700 mL water or normal saline 4
• Administer as a retention enema via rectal balloon catheter 3-4 times per day 4
• The enema solution must be retained in the intestine for at least 30-60 minutes 4, 2
• Do NOT use cleansing enemas containing soap suds or other alkaline agents beforehand 2

Dosing by Clinical Indication

For Constipation

• Initial dose: 15-30 mL (10-20 g) once daily in the evening 1, 3
• Titration: Increase every few days based on response, up to maximum 60 mL (40 g) daily 1, 2
• Goal: 2-3 soft, non-forced bowel movements daily 1
• Position as second-line therapy after over-the-counter options fail 5, 1

For Hepatic Encephalopathy (Overt)

• Acute phase: 30-45 mL (20-30 g) every 1-2 hours orally until patient has at least 2 bowel movements per day 4
• Maintenance: 20-30 g orally 3-4 times per day 4
• Titrate to achieve 2-3 soft stools per day 4
• Continue long-term therapy to prevent recurrence 2

Pediatric Dosing

• Infants: 2.5-10 mL daily in divided doses 2
• Older children and adolescents: 40-90 mL total daily dose 2
• If initial dose causes diarrhea, reduce immediately; if diarrhea persists, discontinue lactulose 2

Critical Monitoring and Side Effect Management

Expected Side Effects

• Bloating and flatulence occur in approximately 20% of patients and are dose-dependent 5, 3
• Starting at lower doses (10-20 g daily) and titrating upward minimizes these gastrointestinal side effects 5, 3
• Abdominal pain and cramps are common and may limit clinical use 3

Serious Adverse Effects Requiring Monitoring

• Monitor serum potassium levels, especially in high-risk populations (elderly, patients on diuretics, hepatic encephalopathy patients on high doses) 3
• Check baseline serum potassium before initiating lactulose and during dose titration 3
• Excessive dosing can cause hypokalemia and hypernatremia 1, 3
• Assess for clinical signs of hypokalemia (muscle weakness, cardiac arrhythmias) 3

Special Population Considerations

• Use with caution in first trimester of pregnancy 1, 3
• Monitor diabetic patients carefully due to carbohydrate content which may require glucose management adjustment 1
• Elderly patients have reduced renal potassium conservation, making them more susceptible to hypokalemia 3

Timeline for Clinical Response

• Improvement may occur within 24 hours but may not begin before 48 hours or even later 2
• For hepatic encephalopathy, reversal of coma may take place within 2 hours of the first enema in some patients 2
• When transitioning from rectal to oral route, start oral lactulose before stopping enema entirely 2

Common Pitfalls to Avoid

• Do not use lactulose as first-line therapy when over-the-counter options haven't been tried for constipation 1
• Do not use alkaline cleansing enemas before lactulose retention enemas 2
• Do not continue lactulose if diarrhea persists in pediatric patients 2
• If inadequate response after 2-4 weeks at maximum tolerated dose (up to 60 mL daily), or if bloating is intolerable, consider adding or switching to senna for short-term use 5