Calculating Pediatric Herbal Dosing

While I’ve been working on the herbal medicine volume for the past year or so, it’s only been in the past six that I’ve felt the urgency of completing the task.  And I’m happy to report that I’m getting close—maybe just another two weeks.  A lot depends on how many holes I find in the material already compiled.  Saturday night I found some omissions that need to be remedied, and pediatric herbal dosing is one of them.

Previous blog articles addressed the issue of calculating pediatric dosages of medications when you only have adult formulations.  Parents found themselves in difficulty when the US experienced shortages of children’s Tylenol and amoxicillin a year or so ago. 

Anyway, it suddenly dawned on me that this new herbal book lacked any guidelines for pediatric dosing.  And the whole reason I started writing the blog and books was for my children and grandchildren.  Duh.

Over the years, several formulas for calculating pediatric dosages have been developed.  I reviewed several of the online calculators, most of which go to great lengths to make simple calculations confusing.

Here are some of the most common formulas:

Clark’s Rule:  Divide the weight in pounds by 150 to obtain an approximate fraction of the adult dose.  For a 50-pound child the calculation would be 50 divided by 150, or one-third of the adult dose.[i]  This calculation should only be used for children aged 2-17 years.

Cowling’s Rule:  Divide the age of the child at her next birthday by 24.  For a 6-year-old girl, divide 6 by 24, or one-fourth of the adult dose.[ii]

Fried’s Rule:  Divide the age of the infant in months by 150.  For a 6-month old baby, that is 0.04.  Multiply that by the adult dose to yield the infant dosage.  Use this calculation for infants.

Salisbury’s Rule:  For children less than 30 kg, multiply the weight in kilograms by 2 to obtain the percentage of the adult dose.  For a child that weighs 15 kg, multiply that by 2 to obtain 30, or 30% of the adult dose. 

For children over 30 kg but less than 70 kg, add 30 to the weight in kilograms to obtain the percentage of the adult dose.  For a child that weighs 50 kg, add 50 to 30 to obtain 80, or 80% of the adult dose.[iii]

Young’s Rule:  Take the child’s age, we’ll use 6 years again, and divide it by 12+ the age of the child, in our case 6 years.  So that would be 6 divided by 12+6, or one-third, for a dose of one-third of the adult dose.[iv]  This calculation can be used when the weight of the patient is not known.

As with all calculations for administered the appropriate dosage, double-check calculations, and even better, have someone else double-check.  All of these rules are just approximations.  You never want to overdose or underdose a patient, and for that reason, performing a few different calculations and then averaging the results wouldn’t be a bad idea, either. 

Links to related posts:

Prepping for Pediatric Drug Dosing 

Candy Flavorings to Add to the Medicine Chest  

Alternative Methods of Administering Medicine 

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[i] Benjamin J. Delgado, et al., Clark’s Rule, StatPearls, 30 July 2023, https://www.ncbi.nlm.nih.gov/books/NBK541104/ (accessed 22 January 2024).

[ii] Calculations for pediatric dosages, Basicmedical Key, https://basicmedicalkey.com/calculations-for-pediatric-doses/ (accessed 22 January 2024).

[iii] I Mahmood, A Simple Method for the Prediction of Therapeutic Proteins (Monoclonal and Polyclonal Antibodies and Non-Antibody Proteins) for First-in-Pediatric Dose Selection: Application of Salisbury Rule, Antibodies (Basel), 21 October 2022, Vol 11 No 4, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9590058/ (accessed 22 January 2024).

[iv] Christian I. Wade, et al., Young’s Rule, StatPearls, 8 April 2023, https://www.ncbi.nlm.nih.gov/books/NBK554603/ (accessed 22 January 2024).