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What Factors Affect a Pediatric Dosage?

By Alex Terris
Updated: Mar 03, 2024

There are a number of factors that could affect the correct pediatric dosage of a medication, although the factors most commonly used in calculations are age and weight. Weight is usually especially important, because it can greatly affect the amount of a drug required to have the desired effect. Other factors that could affect dosages for children include the gender of the child, race and whether the drug is to be taken before or after meals.

Being able to calculate pediatric dosage correctly is essential for anyone prescribing or administering medication to children. A dosage that’s too low may not have the desired effect, while too much of a particular drug can cause unwanted side effects or even death. The two most important factors affecting dosage are weight and age, although there are many others that may need to be taken into consideration.

Weight is usually the factor that has the most effect on the correct dosage. To calculate a child’s dosage, the weight of the child is usually divided by the average adult weight to form a ratio. The adult dosage, which is commonly calculated for a 24-year-old adult, is then multiplied by this ratio to calculate the correct child’s dosage. This method for calculating the dosage is known as Clark’s Rule.

Age is another important factor when calculating a pediatric dosage. In most cases, the younger a child is, the less medication he or she needs to take to produce the desire effect. Calculating a pediatric dosage using a child’s age is similar to the calculation for weight, except the dosage ratio is found by dividing the age of the child by that age plus 12 years. This ratio is then multiplied with the adult dosage to calculate the correct child’s dosage.

Although age and weight are the most commonly used factors when calculating a pediatric dosage, others may have an effect. Females, for example, often require smaller doses than males. The genetic makeup of the child also may affect how he or she reacts to a particular drug, so this may need to be taken into account. Other potential factors include race, the time of day a medication is given and how frequently the drug needs to be taken. The various factors make it essential for a doctor or pharmacist to calculate pediatric dosage, because such professionals are trained to understand the different factors involved.

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Discussion Comments
By bear78 — On Dec 23, 2014

All over the counter pediatric drugs already have a calculation on the label for dosage levels by age and weight. And if we need a prescription drug, my son's pediatrician does the calculation for us and tells us how much my son needs. So I've never had to make a calculation for a dosage myself. But if I do, I'll just follow the formula given here. So far, the dosages given by drug manufacturers and the pediatrician have worked just fine.

By literally45 — On Dec 22, 2014

@ddljohn-- I don't think it's always due to race but I do know that different people have different tolerance levels to medication. A lower dose is effective for some people and this difference can be seen also in childhood.

I think that parents in time understand their child's tolerance levels for medications. My younger daughter for example, who is four, gets affected more by drugs than my older daughter. If I give her the recommended dose, she experiences many side effects. If the medication causes drowsiness for example, it wall cause extreme drowsiness for my daughter and put her to sleep for hours.

I told her doctor this when I noticed and we lowered the dose a little bit. The drug worked better at a slightly lower dose and my daughter had less side effects. So it's not possible to generalize this for all children. Each child is different.

By ddljohn — On Dec 22, 2014

I obviously understand why age and weight is important for determining a pediatric dosage. These factors are actually important for everyone -- child, teenager or adult. But I don't see how gender and race could affect the dosage needed.

I have a son and daughter and my son has not need a larger dose than my daughter. I don't think that two children of different gender but same age and weight should require different doses. I also don't understand what race has anything to do with dosage.

By Melonlity — On Dec 14, 2014

@Vinzenzo -- Like it or not, the fact that companies can get sued so easily has led to them being cautious in the way you have described. I don't have a problem at all with that as the threat of getting sued to kingdom come and losing a bunch of cash tends to keep companies honest.

By Vincenzo — On Dec 13, 2014

It is very important to remember that drug companies build in a substantial "fudge factor" when coming up with recommended dosages for children. That is because they want to make sure to leave enough room to avoid a bunch of lawsuits from parents who didn't read the directions properly.

I am not saying to go nuts and disregard dosage amounts when giving medicine to kids. No, you should stick with those. All I am saying is that the level suggested by drug manufacturers is probably safe.

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