Lactulose is used as a stool softener in cases of constipation and xifaxan is used to fight some causes of diarrhea. But both are treatments for preventing the buildup of ammonia in the blood due to compromised liver function. The ammonia is produced mainly by bacteria in the intestines, from where it is absorbed into the bloodstream. Ordinarily the liver converts this ammonia into urea, which is excreted in urine. If liver function is compromised then ammonia is not effectively removed in this way.
Lactulose works in a few ways to help reduce ammonia circulating in the blood. It helps to draw water, containing ammonia, back into the intestines; it promotes the excretion of ammonia from the bowels; and it helps to promote the growth of intestinal bacteria that do not produce ammonia (which can replace the bacteria that do produce ammonia).
Xifaxan is an antibiotic that is prepared especially to work in the intestines and it directly kills the bacteria that produce ammonia. This reduces the amount of ammonia that gets into the bloodstream in the first place.
Both lactulose and Xifaxan are broadly but not completely effective at lowering levels of circulating ammonia, and some people may do better with one treatment than the other. Also, both have their downsides. Lactulose can lead to intestinal discomfort and it can be difficult for people to maintain their lifestyle if they have to take a laxative two or three times a day. Xifaxan has side effects which can include intense abdominal pain, and a small percentage of people may be allergic to the drug. (Allergies to lactulose are much rarer.)
It is always best to find out from the doctor directly why they have chosen or switched treatments in a particular case. In general, two reasons that a doctor may switch between lactulose and Xifaxan are to see if one is more effective than the other for a particular patient or because the patient may have an easier time with one treatment than the other.
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