How to calculate child medicine dosage

Pediatric Dose Calculator

Created by Łucja Zaborowska, MD, PhD candidate

Reviewed by Bogna Szyk and Steven Wooding

Based on research by

Pan SD, Zhu LL, Chen M, Xia P, Zhou Q. “Weight-based dosing in medication use: what should we know?“ Patient Prefer Adherence (2016)

Last updated: Aug 06, 2022

• How to use the pediatric dose calculator?
• Dose frequency abbreviations
• How do you calculate pediatric doses?
• Child dose calculations examples

The pediatric dose calculator is a simple tool for computing the pediatric dosage for a child of a given weight. 👶

Our calculator allows you to convert values in mg or μg to a precise volume of the medication, using a wide range of units.

The article below is an essential part of our peds dosing calculator - keep on reading to discover all the necessary medical abbreviations, information on pediatric medication dosing, and tips on how to calculate the pediatric dose on your own.

Disclaimer: We try our best to make our Omni Calculators as precise and reliable as possible. However, this tool can never replace professional medical advice.

How to use the pediatric dose calculator?

Pediatric dosage is a complicated matter - we can't deny it. We decided to make things easier for you and explain step-by-step all the actions you need to take to receive the most accurate results.

1. Decide whether your dose is given in mg or μg.

   Milligrams (mg) are 1000 times greater unit than micrograms (μg) - 1 mg = 1000 μg.

2. Find out your type of dosage.

   Your dose in mg/μg might be given:

• per kilogram per day (e. g., mg/kg/day) - the most popular option

• per kilogram per dose (e.g., mg/kg/dose)

• per day (e.g., mg/day)

• per dose (e.g., mg/dose)

  The calculator will display the chosen dosage type underneath.

  Dosage type has a crucial impact on the value of the dosage!
  Only the first two types use the dosage calculator by weight; two latter ones rely on a predetermined amount of medication.

3. Finally, enter your dose amount in mg or μg.

   Double-check all the settings - you want to make sure that the pediatric drug dose calculator is computing exactly what you want it to calculate.

4. Choose the frequency. - check the section below.

5. Choose the weight of your child and a proper unit.

6. Enter your drug concentration.

   Choose the mass of the drug per given volume of the medication.

   The calculator will display the chosen concentration underneath.

7. Yay! Your results are here - it wasn't that hard, was it? 🎉

If you've already found out everything you need to know, you may as well try and discover our other child dose calculations:

• Ibuprofen dosage
• Paracetamol dosage calculator
• Simple dosage calculator
• Epinephrine dose for kids

Dose frequency abbreviations

Dose frequency might be quite misleading since all the abbreviations originate from the Latin language. Here we present a short, useful medical dictionary:

• dQ - once per day
• BID - twice per day
• TID - three times per day
• QID - four times per day
• q4 hr - once every four hours (6 times per day)
• q3 hr - once every three hours (8 times per day)
• q2 hr - once every two hours (12 times per day)
• q1 hr - once every hour (24 times per day)

How do you calculate pediatric doses?

There's one primary dose calculation formula for children:

▪️ mg/μg per kilogram per day

dose (volume) = (dose (mg/μg) * child's weight) / (concentration * frequency)

where:

• concentration is usually given in mg/mL
• child's weight is given in kg
• frequency means the number of times a chosen medication is given per day. E.g., q1 hr frequency has a value of 24.

However, this equation still has to be modified for every other type of dosage! Below, we enumerated all the available pediatric dosage calculations formulas:

▪️ mg/μg per kilogram per dose

dose (volume) = (dose (mg/μg) * child's weight) / concentration

▪️ mg/μg per day

dose (volume) = dose (mg/μg) / (concentration * frequency)

▪️ mg/μg per day

dose (volume) = dose (mg/μg) / concentration

Hey, how about discovering our other professional pediatric tools:

• Maintenance fluids 🚰
• Blood volume 💉
• Blood transfusion 💉
• Growth charts 📈

Child dose calculations examples

Our baby has a fever! 🤒🌡️👶

Still not sure how to calculate pediatric doses? We're going to focus on an mg/kg/day formula since it's the most complex one. Carefully follow the example below:

• We bought some paracetamol to lower the fever - its container states that this syrup's concentration is equal to 120 mg /5 mL. Our prescribed peds dose is 10 mg/kg. Our kid's 4.5 years old and weights 20 kg. We need two doses of paracetamol per day.

How much mL of paracetamol syrup do we need per day?

Let's use the following formula:

dose (volume) = (dose (mg/μg) * child's weight) / (concentration * frequency)

First, let's boil down the concentration:

120 mg/5 mL / 5 = 24 mg / 1 mL = 24 mg/mL

Then come back to the equation itself:

dose (volume) = (10 mg/kg * 10 kg) / (24 mg/mL * 2)

dose (volume) = 100 mg / 48 mg/mL

dose (volume) = 2.083 ≈ 2.1 mL - we need 2. 1 mL of paracetamol per dose, twice per day.

Yay, we got it! You're becoming the true pediatric dose master.

Łucja Zaborowska, MD, PhD candidate

Dosage (weight)

Dosage type

Frequency

Weight

Drug concentration

Dosage (volume)

Dosage

per dose

per 24h

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Clark's Rule - StatPearls - NCBI Bookshelf

Benjamin J. Delgado; Anthony O. Safadi; Tushar Bajaj.

Author Information

Last Update: July 5, 2022.

Definition/Introduction

Clark's rule is an equation used to calculate pediatric medication dosage based on the known weight of a patient and a known adult dose of medication to be used. Clark's rule equation is defined as the weight of the patient in pounds divided by the average standard weight of 150 pounds (68 kg) multiplied by the adult dose of a drug equals the pediatric medication dose, as is demonstrated below:      

• (Weight* divided by 150 lbs. ) x Adult Dose** = Pediatric Dosage

• (Weight*** divided by 68 kg) x Adult Dose** = Pediatric Dosage

*Weight of pediatric patient in pounds (lbs.)

**Adult dose is the recommended dosage for adult medication use

***Weight of pediatric patient in kilograms (kg)

Clark's rule is one of the known pediatric medication dosing rules described in the medical literature that utilizes the patient's weight to calculate medication dosage. Other equations that utilize pediatric weight to calculate medication dosing include Salisbury's rule, Penna's rule, and the Body Surface Area rule. Other methods besides Clark's rule that also utilize pediatric age to calculate radiopharmaceutical medication dosages used in nuclear imaging include Young's rule, Webster's rule, and Fried's rule.[1][2]

Issues of Concern

Pediatric Obesity and Medication Dosing

Data from 2011 to 2014 showed the prevalence of obesity among children and adolescents 2 to 19-year-old of age to be 17% in the United States and continues to increase. [3] In addition to the known numerous health complications and the development of comorbidities associated with pediatric obesity, this epidemic has created challenges to weight-based medication dosing because of the pharmacokinetic changes associated with obesity. For medication distribution, excess adipose tissue in obese pediatric patients has been described to affect a medication's volume distribution (the amount of medication in the body compared to plasma concentration). Lipophilic medications are more likely to have higher volume distribution into adipose tissue when compared to normal-weight pediatric patients. In contrast, hydrophilic medications may have increased or decreased volume distributions, altering the medication loading dose.[4] 

Due to the alterations in medication loading doses, obese pediatric patients may be at risk for either medication toxicity or sub-therapeutic medication therapy. Studies have described the use of ideal body weight for the calculation of hydrophilic medication loading dose, total body weight for lipophilic medications loading dose, and adjusted body weight for a partially lipophilic medication loading dose. [5][6] Pediatric obesity's effects on pharmacokinetic changes in medication absorption, metabolism, and excretion remain an area in need of further research.[4]

Clinical Significance

Medication dosing for pediatric patients is described to use either the following methods for medication dosing: age-based dosing, allometric scaling, body surface area-based dosing, and weight-based dosing; neither method is to be more superior to the other and varies based on a medication's chemical properties and the age of the patient.[7] Weight-based dosing is the most commonly used method for calculating recommended medication doses in pediatric clinical practice.[8] Some have thought that adult medication dosages are universally applied to pediatric patients when in fact, this is a misconception. Pediatric patient pharmacokinetics and pharmacodynamics vary in age, body weight, body surface area, and developmental growth and function of various organ systems compared to adults.[7] 

The absence of deliberate practice in correct pediatric medication dosing can have potential effects such as exposing the patient to suboptimal medication dosages and severe systemic toxicity, which may even result in fatalities.

Nursing, Allied Health, and Interprofessional Team Interventions

Nursing and pharmacy should be familiar with Clark's rule since they will be preparing/dispensing and administering the medications to infants and children. This way, they can add another layer of safety when administering drugs to children and reach out to the prescribing or ordering clinician if they suspect an incorrect dose when using Clark's rule. This interprofessional system of checks and balances can optimize patient outcomes. [Level 5]

Review Questions

• Access free multiple choice questions on this topic.

• Comment on this article.

References

1.

Elias GP, Antoniali C, Mariano RC. Comparative study of rules employed for calculation of pediatric drug dosage. J Appl Oral Sci. 2005 Jun;13(2):114-9. [PubMed: 20924533]

2.

Accorsi R, Karp JS, Surti S. Improved dose regimen in pediatric PET. J Nucl Med. 2010 Feb;51(2):293-300. [PubMed: 20080887]

3.

Ogden CL, Carroll MD, Lawman HG, Fryar CD, Kruszon-Moran D, Kit BK, Flegal KM. Trends in Obesity Prevalence Among Children and Adolescents in the United States, 1988-1994 Through 2013-2014. JAMA. 2016 Jun 07;315(21):2292-9. [PMC free article: PMC6361521] [PubMed: 27272581]

4.

Kendrick JG, Carr RR, Ensom MH. Pharmacokinetics and drug dosing in obese children. J Pediatr Pharmacol Ther. 2010 Apr;15(2):94-109. [PMC free article: PMC3018176] [PubMed: 22477800]

5.

Kendrick JG, Carr RR, Ensom MH. Pediatric Obesity: Pharmacokinetics and Implications for Drug Dosing. Clin Ther. 2015 Sep 01;37(9):1897-923. [PubMed: 26361823]

6.

Matson KL, Horton ER, Capino AC., Advocacy Committee for the Pediatric Pharmacy Advocacy Group. Medication Dosage in Overweight and Obese Children. J Pediatr Pharmacol Ther. 2017 Jan-Feb;22(1):81-83. [PMC free article: PMC5341538] [PubMed: 28337087]

7.

Bartelink IH, Rademaker CM, Schobben AF, van den Anker JN. Guidelines on paediatric dosing on the basis of developmental physiology and pharmacokinetic considerations. Clin Pharmacokinet. 2006;45(11):1077-97. [PubMed: 17048973]

8.

Pan SD, Zhu LL, Chen M, Xia P, Zhou Q. Weight-based dosing in medication use: what should we know? Patient Prefer Adherence. 2016;10:549-60. [PMC free article: PMC4835122] [PubMed: 27110105]

Children's dosage: measure correctly - Letidor

Despite the fact that the dosages are indicated in the instructions for the drug, the question: "How to calculate the amount of medicine for a child?" - I hear it very often. And this is good. It is much worse if the mother does not think about it and gives the baby an extra second or even third pill to enhance the effect.

But even if parents understand the meaning of children's dosage, they do not always know the practical details. For example, not all tablets can be cut in half, and not all teaspoons are equally useful in measuring five milliliters.

There are two main doses for any drug:

Maximum single dose - how much you can drink at one time.
Maximum daily is the total amount of medication per day.

They are especially important for over-the-counter products, the instructions for which parents rarely read, considering them harmless. Which is not true at all. These doses should not be exceeded in any case, the consequences can be varied, but always unpleasant, sometimes even downright dangerous. From the instructions, you can generally learn a lot of interesting things, for example, that acetylsalicylic acid should not be given to children under 12 years old.

Children's doses are calculated based on body weight. Age also matters, but if a too well-developed girl weighs 40 kg at 10 years old, she will need the same amount of the drug as a 15-year-old asthenic boy with the same weight. That is why all instructions indicate not only the age, but also the weight category of the child.

Example: Maximum daily doses of paracetamol (do not forget to count ALL paracetamol included in hot drinks, syrups, suppositories, etc.).

• up to 6 months (up to 7 kg) - 350 mg
• from 6 months to a year (up to 10 kg) - 500 mg
• 1-3 years (up to 15 kg) - 750 mg
• up to 22 kg) — 1 g
• 6–9 years (up to 30 kg) — 1.5 g
• 9–12 years (up to 40 kg) — 2 g

Important! There are no universal rules for calculating the dose that could guarantee the effectiveness and safety of the use of drugs in children, especially newborns. The pediatrician should correctly prescribe the drug.

Many people think that it is enough to split a tablet in half and the required dosage will be observed! You can break it only if there is a special groove. In other cases, special medicines with multiple doses are required. Why is it so?

Firstly, during production it is almost impossible to mix the mass to a homogeneous state and make sure that exactly 50% of the necessary ingredients are in the half. Studies have shown that this percentage ranges from 20 to 80. And the spread of dosages will be the higher, the more components in the drug.

Secondly, in addition to the main active ingredient in the tablet, there is also a lot of auxiliary, added not at all in a 1:1 ratio. And when dividing them, it will turn out less than what is required for the correct "work" of the medicine.

_ Important! Never replace "baby" doses with half or quarter "adult" doses. This is fraught with an overdose, especially in young children. _

Liquid dosage forms are sometimes measured incorrectly. Most people are sure that a teaspoon is 5 ml, a dessert spoon is 10 ml, and a tablespoon is 15 ml. But firstly, there are tablespoons and 20 ml each, and teaspoons - 7.5 ml each. Secondly, not everyone fills even a standard spoon exactly to the brim.

American scientists from Cornell University conducted a study, and it turned out that when using medium-sized spoons, patients receive 8.4% less of the drug, and when measuring the remedy with large spoons, 11.6% more. At the same time, every fifth participant in the experiment was sure that in both cases the medicine would give the same effect.

The consequences of a single over- or underdose are insignificant, but for people who have to take the medicine every 4-8 hours for several days, this difference between the recommended and actual dose can be significant.

_ Important! Use cutlery only if the medicine does not come with a special measuring container - a cap or a spoon. _

The most difficult situation is with the use of medicinal plants in children. Unfortunately, the recommendations on the packages, as a rule, apply only to adult patients. Many mothers brew herbs for a child “as written on the pack”, that is, an adult dose, and at the same time receive an overdose of a medicinal substance, which can result in allergic, toxic reactions, and deterioration in well-being. But the herbs will be completely innocent! So that they give only strength and health, we present the most commonly used children's dosages.

Dosages of herbs and herbs (based on 2 days):