If i switch from lactulose to neomycin, will it start working right away?

Maybe in your case: Assuming you have confusion due to your liver disease called hepatic encephalopathy, some people don't respond to lactulose over time or might not like the taste or bloating associated with it, so other medications like antibiotics (neomycin, Flagyl and rifaximin) are used. Antibiotics take a couple days to work. Neomycin requires your hearing to be checked as it can cause hearing loss.