Acetaminophen Dose Prescribed for Children Often Incorrect

Steven Fox

May 27, 2011

May 27, 2011 — Primary care physicians in Scotland often incorrectly prescribe the analgesic/antipyretic paracetamol to pediatric patients, giving less than the recommend doses to older children or exceeding recommended doses in young children.

That is the principal finding from a study of nearly 36,000 children aged 0 to 12 years that was published online May 18 in the British Journal of Clinical Pharmacology. The authors say it is the first study to describe patterns of paracetamol prescribing by primary care physicians in the United Kingdom. Paracetamol, which is the international nonproprietary name for the drug, is called acetaminophen in the United States, per the US Alternate Name Council.

Senior author James McLay, MBChB, PhD, from the Division of Applied Health Sciences, University of Aberdeen, Royal Aberdeen Children's Hospital, Scotland, said he and his team found that more than half of the prescriptions written by primary care physicians failed to comply with current recommendations from the British National Formulary for Children. "Paracetamol off label prescribing is common in primary care, with relatively high levels of potential overdosing in the youngest children and potential underdosing in the oldest children," Dr. McLay and colleagues write.

The source of the data was 35,839 children aged 0 to 12 years who were included in the Scottish Practice Team Information database in 2006.

During the study year, primary care physicians wrote a total of 4423 paracetamol prescriptions for pediatric patients. About 49% were written for children aged 1 to 5 years.

Eighteen percent of paracetamol prescriptions were off-label, the researchers said, and accounting for repeat prescriptions, nearly 23% of children were exposed to off-label uses of the drug. "A further 15% of prescriptions contained no dosage instruction at all," the researchers said.

About 11% of all prescriptions were classified as underdosing, and 2.9% as overdosing. An additional 15% of the prescriptions contained no dosing information other than "as required."

The researchers said that age was significantly linked to nonrecommended dosing. Young children (those aged 1 - 3 months) were found to be at the greatest risk of being overdosed. About 27% of prescriptions recommended an actual or a potential overdose, and a quarter of the children aged 6 to 12 years were given an actual or potential underdose.

In total, 57.2% of all the prescriptions written failed to follow the current recommendations of the British National Formulary for Children, the authors said.

"The reasons for these prescribing patterns are unclear, however it is possible that in the absence of reports relating to underdosing and treatment failure, primary care physicians have been sensitised by earlier reports of paracetamol overdosing and hepatotoxicity," the authors write.

In addition, "[i]t is recognised that up to 50% of parents do not understand official dosage recommendations for medicines such as paracetamol, and absence of dosing instructions can leave parents in a state of confusion, or strengthen the public perception that paracetamol is harmless," Dr. McLay and colleagues write.

Dosing Acetaminophen Based on Age, Not Weight, "Is Trouble"

Similar concerns in the United States were reflected in a set of new recommendations from an advisory panel of the US Food and Drug Administration (FDA) that were issued just last week, with the panel saying pediatric doses of acetaminophen should be based first on a child's weight, then on age.

In addition to that recommendation, the panel also said that for use in children younger than 2 years, acetaminophen should be labeled only for reduction of fever. For children older than 2 years, the drug can be labeled for both fever reduction and pain relief.

The American Academy of Pediatrics' Committee on Drugs was one of the groups that testified at the FDA. Daniel Frattarelli, MD, who acts as chair for that committee, provided several comments on the current Scottish study, via email, to Medscape Medical News.

"This study underscores the importance of proper dosing of all medications for children." Dr. Frattarelli noted. He added that in the United States, acetaminophen is given by parents as an over-the-counter drug, "so for most kids, the incorrect prescribing by physicians discussed in this article isn't a problem."

Pediatricians dose acetaminophen by weight, but the current over-the-counter FDA labeling for acetaminophen is by age, and Dr. Frattarelli acknowledged that this can lead to trouble.

"Going to a school recital will show that there is a lot of variability in the sizes of kids who are the same age, let alone those over several years. So when parents are told to dose by age instead of weight, there are 2 potential problems: the larger child may not receive as much drug as his or her body needs, and so may suffer from decreased efficacy, while the smaller child may receive too much and be at greater risk for toxicity."

He said he feels the recent push to change recommendations to weight-based dosing for acetaminophen is a positive step.

"Another potential source of incorrect dosing is in the measurement. Parents often use a silverware teaspoon to measure liquid medications, not realizing that these are inaccurate," he said. The recent recommended changes also address that concern and would require manufacturers of liquid acetaminophen to include a measuring device clearly marked in milliliters, using the standard "mL" abbreviation.

One other change is that the advisory panel recommended that to avoid parental confusion, all solid pill forms of acetaminophen for children be available in a single concentration.

Another member of the FDA Committee on Drugs, Ian Paul, MD, professor of pediatric health sciences at the Penn State College of Medicine, Hershey, said in a telephone interview with Medscape Medical News: "Certainly we know that parents sometimes misuse medications, and [we] know that parents aren't necessarily properly informed about the drugs they're giving their children."

He pointed out, however, that acetaminophen is the most widely used drug in children — period — and that there are many products that contain that agent, either as the sole ingredient or as 1 of several ingredients.

"So it's not surprising there would be some confusion among [general practitioners] and parents about proper dosing." He said he hopes the new recommendations help clarify some of these issues.

The study was supported by the Scottish Medicines for Children Network. The authors, Dr. Frattarelli, and Dr. Paul have disclosed no relevant financial relationships.

Br J Clin Pharmacol. Published online May 18, 2011. Full text

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