Is there any way that you could check with the Dr who prescribed it? My DS has been prescribed 10 ml doses a couple of times since the age of 5, and I was told by the Dr that children should be prescribed the adult dose from that age. The pharmacy that I've taken the prescriptions to has always questioned the dosage when I've handed it over, so I'm not sure that they would be the ones to ask. 9 ml does seem an unusual dose too.
We got prescribed amoxicillin 2x 5ml 3 times a day for 5 days by a locus. We queried length of prescription with GO surgery as it was for Scarlet Fever and we though a longer course was needed. GP said that was almost Iv strengt antibiotics and reduced it down to 1 x 5mls for 7 days.
She also confirmed that it wouldn’t do any harm ( we had been giving him that for 2 days)
Just checked in the BNF and if it's the 250mg/5ml suspension then it is perfectly fine. 9ml would be 450mg. Standard dose is 250mg for 1-4 year olds (500mg for 5-11 year olds, so he's on the cusp really) but he can have up to 30mg per kilo (so if he's 25kg, that would be 750mg) three times a day so absolutely fine.