That is a tough one because I think there is a 'normal' dose that you would start with (based on weight) then some babies need a larger dose than that to actually get it under control.

Most of the people I know who have got Losec for 8-10 week olds were put on 10mg per day, some stayed at that amount and some had it increased because 10mg didn't cut it. DD2 would have been about 3.5kg when she got it prescribed and her doctor said 5mg. I've recently upped it to 10mg because the really bad pain was making an appearance again with 5mg - I guess she had got big enough for the dose to need to increase??

I am definitely not a medical expert, so I am really not qualified to comment, but 2.5g sounds like a lower dose than what I've heard of other babies (even littlies like ours) having so I would suggest getting a second opinion on the dose, even if they tell you that the 2.5mg is correct, it is worth it for your peace of mind.