Pulmonary Hydrogen and Methane and Plasma Ammonia after the Administration of Lactulose or Sorbitol

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Abstract
The gut microfloral metabolism of sorbitol and lactulose was investigated in 10 healthy control subjects and 10 patients with cirrhosis of the liver, by measuring the pulmonary excretion of the fermentational gases H2 and methane during 3 h. A possible acute effect on venous plasma ammonia aftr a single dose of sorbitol or lactulose was also investigated. No significant difference in fermentation gas excretion was found after ingestion of sorbitol compared with lactulose in healthy controls or cirrhotic patients (P > 0.05). Neither sorbitol nor lactulose had significant effect on plasma ammonia concentrations during the first 3 h after ingestion. Since both sorbitol and lactulose are extensively fermented by the colonic flora, the possibility of replacing lactulose with the much cheaper sorbitol in the treatment of portosystemic encephalopathy should be investigated. The suggested acute gut-ammonia trapping effect of lactulose caused by acidification of the gut lumen from fermentative end-products was not supported by the present findings.