PORTALAC
Clinical safety rating: caution
Comprehensive clinical and safety monograph for PORTALAC (PORTALAC).
Lactulose is a synthetic disaccharide that is not absorbed from the gastrointestinal tract. It is metabolized by colonic bacteria to short-chain fatty acids (e.g., acetic, lactic, and formic acid), resulting in acidification of colonic contents and an increase in osmotic pressure, which stimulates bowel evacuation. In hepatic encephalopathy, acidification reduces blood ammonia levels by converting NH3 to NH4+ in the colon, inhibiting ammonia absorption.
| Metabolism | Not metabolized in the small intestine; metabolized by colonic bacteria (e.g., Lactobacillus, Bacteroides) to organic acids (lactic, acetic, formic) and gases (CO2, H2). |
| Excretion | Renal: ~40% as unchanged drug; fecal: ~60% as metabolites (biliary excretion of conjugates and lactulose). |
| Half-life | 1.7-2.0 hours (terminal); clinical context: short t1/2 allows rapid dose adjustment in hepatic encephalopathy. |
| Protein binding | <10% bound to plasma proteins (albumin). |
| Volume of Distribution | 0.25-0.5 L/kg; distributes primarily in extracellular fluid. |
| Bioavailability | Oral: <2% (poor systemic absorption due to gut metabolism); rectal: <5% absorbed. |
| Onset of Action | Oral: 24-48 hours for laxative effect; rectal: 30-60 minutes for catharsis. |
| Duration of Action | Laxative effect: 4-6 hours after oral dose; ammonia reduction: sustained with TID dosing. |
Initial: 15-30 mL (10-20 g lactulose) orally, 2-3 times daily; titrate to 2-3 soft stools daily. For acute hepatic encephalopathy: 30-45 mL (20-30 g) orally every hour until evacuation, then 3-4 times daily.
| Dosage form | SOLUTION |
| Renal impairment | No dosage adjustment required for renal impairment; monitor for electrolyte disturbances (hypernatremia) due to diarrhea. |
| Liver impairment | No dosage adjustment required for hepatic impairment; use with caution in severe hepatic encephalopathy due to increased risk of electrolyte imbalance. |
| Pediatric use | Infants: 2.5-10 mL (1.7-6.7 g) daily in divided doses; older children: 15-30 mL (10-20 g) daily, adjusted to produce 2-3 soft stools per day. |
| Geriatric use | Initiate at lower doses (e.g., 15 mL orally once daily) and titrate slowly to avoid excessive diarrhea and dehydration; monitor electrolytes and renal function. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for PORTALAC (PORTALAC).
| Breastfeeding | Safe during breastfeeding due to negligible systemic absorption; M/P ratio not determined as drug acts locally in gut and is not absorbed. |
| Teratogenic Risk | No evidence of teratogenicity in animal studies; limited human data but considered low risk across all trimesters due to minimal systemic absorption. |
| Fetal Monitoring | Monitor serum electrolytes, renal function, and fluid balance in prolonged use or high doses. No specific fetal monitoring required. |
■ FDA Black Box Warning
None
| Serious Effects |
["Hypersensitivity to lactulose or any component of the formulation","Patients on a low-galactose diet (lactulose contains galactose and lactose)","Gastrointestinal obstruction or perforation","Undiagnosed abdominal pain (especially in children)"]
| Precautions | ["Use with caution in patients with galactose intolerance, Lapp lactase deficiency, or glucose-galactose malabsorption due to lactose content.","May cause electrolyte disturbances (e.g., hypernatremia) with prolonged use, especially in elderly or debilitated patients.","Risk of excessive flatulence, abdominal cramping, and diarrhea; adjust dose accordingly.","Use in hepatic encephalopathy: monitor serum electrolytes and ammonia levels; ensure adequate hydration.","Avoid concomitant use with other laxatives unless directed by a physician."] |
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| Fertility Effects | No known adverse effects on fertility based on available data. |