Hepalac Mechanism of Action

Pharmacodynamics: Mechanism of Action: Lactulose, a synthetic disaccharide analog of lactose containing galactose and fructose, decreases blood ammonia concentrations and reduces the degree of portal - systemic encephalopathy.
The human GI tissue does not have an enzyme capable of hydrolysis of this disaccharide; as a result, oral doses pass to the colon virtually unchanged. After reaching the colon, lactulose is metabolized by bacteria resulting in the formation of lactic acid, formic acid, acetic acid and carbon dioxide. These products produce an increased osmotic pressure and slightly acidify the colonic contents, resulting in an increase in stool water content and stool softening. Because the colonic contents are more acidic than the blood, ammonia can migrate from the blood into the colon. The acid colonic contents convert NH₂ to the ammonium ion [NH₄]⁺, trapping it and preventing its absorption. The laxative action of the lactulose metabolites then expels the trapped ammonium ion from the colon.
Pharmacokinetics: Lactulose is poorly absorbed. When given orally, only small amounts reach the blood. Urinary excretion is ≤ 3% and is essentially complete within 24 hours. Lactulose does not exert its effect until it reaches the colon. Transit time through the colon may be slow; therefore, 24 to 48 hours may be required to produce a normal bowel movement.
Onset: Constipation: up to 24 - 48 hours to produce a normal bowel movement.
Encephalopathy: at least 24 - 48 hours.
Absorption: not appreciable.
Metabolism: Via colonic flora to lactic acid and acetic acid requires colonic flora for drug activation.
Excretion: Primarily feces, urine (≤ 3%).