I don't know why it took me 28 years to come up with this formula. Makes my life that much easier. So you are writing for amoxicillin suspension 400 mg/5mLs. Not sure why anyone would use the 250/5 or 125/5 as 400/5 still gives you a good sig amount.
Anyway, as everyone knows the dosing for an ear infection is 90 mg/kg/day divided bid. So, I would have an 11 kg kid and think 11 X 90 = 990 mg divided by 2 = around 495 mg bid = divided by 80 = 6.19 mLs bid. (Obviously you round it off)
But you can simply remember 0.56 (I suppose 0.55 is fine) times the kgs and you have the ~ same amount each time, i.e., 0.56 times 11 = 6.16 mLs. Works every time. You could do it with other sigs but I use 400 mg/5mLs so often, It saves you time and you will make less errors.
