Well, it's not something toxic or strong I guess, but I definitly would not. Giving randomly human medizine without knowing if high acidicy is the problem (never heard of that with rabbits) is not a good idea.
What kind of gastro-intenstinal problems does he have? Can you give more info, also about his diet?
I don’t know what that is, so not sure. If your rabbit has just started to show signs of stasis (reduced appetite, small poops etc), you can use baby gas drops or simethicone. But if it has been more than 8 hours, it’s time for a rabbit-savvy vet