I am really sorry that your son has received wrong dosage. First thing to keep in mind is stop being anxious. Your child is going to be ok.
Recommended maximum dosage of paracetamol
is 75mg/kg/day and for ibugesic is 40mg/kg/day.
Assuming your child's weight as 10 kg, he has received 60mg/kg/day of para and 40mg/kg/day of ibugesic. Thank god he received only two doses a day.
Is there any test which can detect overdosage ?
At present he has not reached criteria for overdosage. But let him be under constant monitoring by pediatrician
. He will check his clinical wellbeing, and if needed can order blood paracetamol levels.
Liver function tests may also be needed if child becomes unwell like vomiting
Any side effects that can occur which we are not able to see externally ?
Only major side effect will be liver damage
which usually manifests as symptoms like vomiting. Child cannot be normal outside and severe damage cannot occur inside.
Good medications are available like N-acetylcysteine
which can be given if needed for the liver to recover.
Regarding rash, its a known side effect for ibugesic which can occur in 1-3% of people who take ibuprofen
. It has nothing to do with overdosage.
Don't worry everything will become alright.