Jenk, what do you mean by Lactulose?
Over 10 years ago Buttercup was sick with tummy problems. We brought him to a Exotic Vet, he told us not to waste are money on medication to go buy Bio Best Plain Yogurt. He said it worked wonders on the bunnies and to be honest it always worked when we gave it to Buttercup, Wilbur and Jackie. We did give it to the others too. I didn't know about Ovol at that time. We just syringed it in his mouth slowly.
Never gave sub q's, would syringe H2O.
I'm not sure if this is the info you are looking for. I know many people on here don't agree with dairy products fir bunnies but they worked for me and it was a Vet who deals with rabbits that told me about it.