Finding the right dosing for obese pediatric patients

Determining the correct medication dosing for obese pediatric patients is extremely challenging and data on the subject is limited, according to Brady Moffett, PharmD, MPH, clinical pharmacy specialist at Texas Children’s Center and assistant professor of pediatrics at Baylor College of Medicine.

Moffett recently addressed the challenges - and provided some dosing guidance - during the Wolters Kluwer Clinical Drug Information webinar “Drug Disposition in Obese Pediatric Patients.”

“We use weight-based dosing, and there are a lot of concerns about what the maximum dose is. It is difficult to reconcile that an adult may be getting a lower dose than an 11 year-old patient,” Moffett said. “There are also a lot of concerns about overdosing.”

Confounding issues

The challenges start with the fact that much of the literature on drug dosing differs on the definition of “obese.” Moffett follows the guideline that obesity in pediatric patients between the ages of two and 18 is determined by a Body Mass Index (BMI) greater than the 95th percentile for age and sex; while an “overweight” patient has a BMI in the 85th-to-94th percentile range.

Another factor to consider is that obese patients typically have decreased metabolic activity, a major element in determination of the effective dose. However, obesity may decrease the metabolism of certain medications such as propranolol, so higher doses may be needed in certain cases.

Another confounding issue is the lack of dosing data in the pediatric population. Moffett and colleagues conducted a web search for dosing of obese pediatric patients admitted to the hospital and receiving acetaminophen, morphine, and hydrocodone. “We came up with almost nothing on pediatric obese dosing of these medications,” he said.

Of the limited data available, some studies indicate that obese pediatric patients may require a higher dose of certain medications, such as warfarin, than non-obese pediatric patients would receive.  “[For warfarin], we may need to increase the maximum dosing guidelines for initial dosing,” Moffett said.

Helpful steps

To determine the correct dosing for pediatric patients, Moffett offered the following suggestions:

· Identifying obese pediatric patients is the first step. “Identify who is obese and who is not. For many patients, it is really difficult to tell unless there are objective measures,” he said.

· Develop a best practices guideline for dosing in obese pediatric patients. As a guide, pharmacists can refer to the American Journal of Health-System Pharmacy clinical report “Development of recommendations for dosing of commonly prescribed medications in critically ill obese children.”

· Use serum concentration monitoring when available.  

· Closely monitor obese pediatric patients’ medication dosing and outcomes. Then, report on the experiences so that everyone has the knowledge.