Young's Rule is an equation used to calculate pediatric medication dosage based on the age of the patient, as well as the known recommended adult dose. The definition of Young's Rule is the age of the patient, divided by the age added to twelve, all multiplied by the recommended adult dose. This formula appears below:

[Age / (Age + 12)] x Recommended Adult Dose = Pediatric Dose

Young's Rule can be applied to quickly approach a situation in which the patient's weight is unknown. Other approaches to pediatric dosing that also use age include Webster's Rule and Fried's Rule. 

If the weight of the patient is known, Clark's Rule or the Body Surface Area rule can be implemented.[1]

Pediatric dosing based on one's age has the potential for suboptimal therapeutic levels due to the broad range of potential weight, especially with increasing childhood obesity.[2][3]

In situations where the pediatric patient's weight is unknown, for instance, at the point of injury, then Young's Rule can be safely implemented if their age and the recommended adult dosing are known. Additionally, certain classes of medications require weight-based dosing, such as antibiotics and antiepileptics. Ultimately, age-based dosing has demonstrated to be a safe and effective approach. However, caution should be used depending on the class of the drug.[4][5]