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Abstract
Aims Childhood obesity is increasing in the UK and worldwide. Recent Public Health England data confirms that in England 19.1% of year-6 school children are obese and 14.4% are overweight. It is also recognised that increased fat and lean masses in obese children affect pharmacokinetics and the distribution of drugs in tissues. Using the child’s Total Body Weight (TBW) to calculate doses could result in incorrect dosing. This study was prompted by an incident of drug toxicity in an obese child where a very large dose was administered based on TBW. We aim to assess whether paediatric doctors have knowledge about prescribing correct doses of medications for obese children by using methods to calculate the ‘Ideal Body Weight’ (IBW).
Method A questionnaire was sent to all paediatric trainees and consultants in the region asking whether they take into account the patient’s weight when prescribing for obese children, whether they understand ‘IBW’ and how to calculate it using the McLaren method.
Results Of the respondents, only 3% (3/109) calculated BMI and determined if the child was obese for its age when prescribing medications.
35% (38/109) of prescribers gave special considerations to the weight when calculating drug doses in obese children
16% (17/109) of prescribers are familiar with, and understand, the terms Total Body Weight (TBW), Ideal Body Weight (IBW), Adjusted Body Weight (ABW) and Lean Body Weight (LBW)
Conclusion The findings suggested that most paediatric prescribers did not ascertain if a child was obese when calculating drug doses. There was relatively poor understanding about the concept of IBW, which is the recommended weight to be used for dose calculations for certain drugs. We noted that although the British National Formulary for Children (BNFC) highlighted which drugs need IBW estimation, it did not provide a method for calculating it. These deficiencies should be addressed at the medical student and junior doctor level with appropriate prescribing training. In addition, the BNFC should include more guidance about calculating IBW in obese children to avoid potentially toxic errors.
9% (10/109) of prescribers knew how to calculate IBW using the McLaren method