Clark's rule

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Clark's rule is a medical term referring to a mathematical formula used to calculate the proper dosage of medicine for children aged 2–17.[1]


The procedure is to take the child's weight in pounds, divide by 150 lb, and multiply the fractional result by the adult dose to find the equivalent child dosage. For example, if an adult dose of medication calls for 30  mg and the child weighs 30 lb, divide the weight by 150 (30/150) to obtain 1/5 and multiply 1/5 times 30 mg to get 6 mg.

Clark's rule is not used clinically, but it is a popular dosage calculation formula for pediatric nursing instructors.[citation needed]

The formula was named after Dr Cecil Belfield Clark (1894–1970), a Barbadian physician who served in London Boroughs for 50 years and was an early advocate for homosexuality rights.[citation needed]

Fried's rule[edit]

Similar to Clark's rule is Fried's rule, by which the formula is modified to be used for infants.[2] The formula is nearly identical, except with the child's weight replaced by the infant's age in months.

Fried's rule was named after Dr Kalman Fried (1914–1999), an Israeli geneticist and pediatrician who developed his own formula while treating and observing children at the University of Jerusalem affiliated Hospital – Hadassah Medical Center in the 1960s. Dr Fried though was more renowned as a geneticist rather than a pediatrician.[citation needed]

Young's rule[edit]

The earlier Young's rule[1] for calculating the correct dose of medicine for a child is similar: it states that the child dosage is equal to the adult dosage multiplied by the child's age in years, divided by the sum of 12 plus the child's age.

Young's rule was named after Dr Thomas Young (1773–1829), an English polymath, physician and physicist.[3]


  1. ^ a b "Clark's rule and Young's rule". Pharmacy Tech Study. Retrieved 14 February 2018.
  2. ^ "Fried's rule". Pharmacy Tech Test. Retrieved 14 February 2018.
  3. ^ Robinson, Andrew (2006). The Last Man Who Knew Everything. Oneworld Publications. p. 2. ISBN 978-1851684946.

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