Clarks rule and Youngs ruleClark's rule and Young's rule are two of several different methods of calculating pediatric dosages. These methods are used when either the manufacturer has not recommended dosages for children or the prescriber has requested them to be used. The best explanation for these is simply that children vary so much in weight, size, tolerances, etc. Clark's RuleClark's Rule uses Weight in Lbs, NEVER in Kg.Here is the formula: Adult Dose X (Weight ÷ 150) = Childs Dose Example 11 year old girl / 70 Lbs 500mg X (70 ÷ 150) = Child's Dose 500mg X ( .47 )= Child's Dose 500mg X .47 = 235mg Child's Dose = 235Mg By Zita Schmitt, CPhT Young's RuleYoungs Rule uses age.(which makes it easier to remember, the word young refers to age) Here is the formula: Adult Dose X (Age ÷ (Age+12)) = Child's Dose Example 11 year old girl / 70 Lbs 500mg X (11 ÷ (11+12)) = Child's Dose 500mg X (11 ÷ 23) = Child's Dose 500mg X .48 = Child's Dose Child's Dose = 240mg By Zita Schmitt, CPhT Dosage based on weightOften drugs are prescribed based on an adults or childs weight in order to more accurately dose. The calculation is very simple and easy to perform. However, you must pay close attention to whether the dosage has been prescribed per Kg or Lbs.Example: 132 Lb woman is prescribed Acyclovir 5mg/kg First convert Lbs. to Kg (132 ÷ 2.2) = 60kg The prescription calls for 5mg per kg 60 x 5mg = 300mg By Zita Schmitt, CPhT Where would you like to go now? Back to Math Homepage Back to Homepage Site Map Clarks rule - top of page Accurate dosage calculations are very important in pharmacy. The tutorial on this website is strictly for the purpose of practicing and preparing for the PTCB or ExCPT exams. Pharmacy Technicians are relied on to calculate standard and non-standard dosages every day. However, a pharmacist is ultimately responsible for all medications and will have the final call on which methods, formulas and calculations are to be used. This website is for informational, educational and entertainment purposes only. Always consult a licensed medical doctor or pharmacist before determining any dosage calculation. If you have any questions, please use the contact page |
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