The term posology is derived from the Greek words “posos,” meaning how much, and “logos,” meaning science. It is a branch of medical science that deals with the dose or quantity of drugs that needs to be administered to a patient to get the desired pharmacological action.

Dosing of drugs in infants and children requires thorough consideration of the differences in the pharmacokinetics and pharmacology of a specific drug. The variation in the body composition and the maturity of liver and kidney functions are the potential sources of differences in pharmacokinetics with respect to age. One of the most arduous tasks in pediatric therapy is the calculation of dosage for children, particularly newborn babies, premature babies, infants, and very young children.

Various methods have been reported to calculate the dosage for children and infants, all of which calculate the child’s dose as a fraction of the adult dose. In general, the formulas used to calculate the child dose use the following criteria:

1. Age of the child
2. Body weight of the child
3. Body surface area of the child