How Should Medications Be Dosed in Obese Children?

Jessica C. Stovel, RPh


September 03, 2013


How should medications be dosed in obese children?

Response from Jessica C. Stovel, RPh
Adjunct Assistant Professor, Department of Psychiatry, Division of Child and Adolescent Psychiatry, Schulich School of Medicine and Dentistry, University of Western Ontario, London, Ontario, Canada

Childhood obesity has been increasing dramatically over the past several years, with its prevalence doubling or tripling between the 1970s and 1990s in numerous countries worldwide.[1,2] In 2010, the World Health Organization estimated that over 42 million children younger than 5 years are overweight and about 75% of these are from developing countries.[3]

This population may be at risk for therapeutic failure or adverse drug effects. One retrospective study found a statistically significant difference in the overall mean dosing error rate per admission in overweight vs control children aged 5-12 years requiring antimicrobials or analgesics. Of interest, underdosing errors occurred most frequently.[4]

Healthy Weight, Overweight, or Obese?

The first step in selecting the most appropriate medication dose for a child is to determine whether the child a healthy weight, overweight, or obese.[5]

The Centers for Disease Control and Prevention recommends using the body mass index (BMI) (weight [kg]/height [m2]) as the primary way to determine whether a child aged 2-19 years is overweight or obese.[6] Although the BMI does not directly determine the specific amount of body fat, it does provide a reasonable indicator of the amount of body fat present.[6]

Once the BMI is calculated, it can then be compared with the reference BMI standards for other children and adolescents aged 2-19 years who are the same age and sex,[7] using the CDC BMI percentile:[6]

  • 5th to < 85th BMI percentile: healthy weight;

  • 85th to < 95th BMI percentile: overweight; and

  • ≥ 95th BMI percentile: obese.

Weight-based Dosing in Children

In general, the correct dose of a medication for a pediatric patient is calculated on the basis of their weight (mg/kg) or body surface area (mg/m2).[1,8] Age, as a surrogate for normal size and function, may also be considered.[1,7]

There are currently no data in the literature to suggest a specific weight at which the adult dose should be used. In general, however, the dose should no longer be increased on the basis of weight or body surface area once the maximum adult dose for a particular medication has been reached.[8,9] Alternatively, some literature suggests that weight-based dosing calculations are most appropriate in children weighing less than 35 or 40 kg.[5,10]

The Pediatric Pharmacy Advocacy Group (PPAG) recommends weight-based dosing for children younger than 18 years of age who weigh less than 40 kg. For those weighing more than 40 kg, clinicians should keep in mind that the dose or dose per day should never exceed the recommended adult dose for the specific indication or medication.[5]


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