computation for giving medicine to infants?

is it based on the freight? if it is an "infant medicine," such as children's ibuprofen suspension, it is base on weight, or consignment and age for some drugs.
if it is an adult medication, probability are 1) the medication is completely unsafe for children or 2) it is impossible to give a small adequate dose without using some remarkably accurate instruments (balances that go to six decimal places, etc.).
for prescription meds, the best piece is to visit your doctor, enjoy him/her examine your child, and ask all your question there. most answers you can bring back from YA! aren't going to be of any use because these people don't know you or your household. (much of pharmacokinetics is genetic. gender and age also play foremost roles.)
for over-the-counter, ask for a consult at your local pharmacy. i've never been anywhere that charges for this service, they singular sell medication. advice is free. they enjoy various charts and medical reference that most people don't own access to, and they can tell you an appropriate dose if it isn't specified on the bunch insert.
just hang on to in mind that any chemical that go through the body needs to be metabolized. usually this is done by metabolic enzymes within a healthy liver, but a child's liver may be too unused to handle enduring compounds. an active drug may be safe while its metabolic byproducts can be toxic, and if the liver doesn't clear those away quickly adequate, your treatment may do more harm than well brought-up.
best to ask your doc on this one
Some are based on solidity, some on age, some on other bases. You must consult your doctor.