Review of commonly used age based weight estimates for paediatric drug dosing in relation to the pharmacokinetic properties of resuscitation drugs

Abstract

Aim To study which weight estimate calculation used in paediatric resuscitation results in optimal drug dosing, the calculations comprising of the three new Advanced Paediatric and Life Support (APLS) age based formulae or the UK Resuscitation Council age based formula. Method Commonly used drugs used in paediatric resuscitation were selected and a literature search conducted for each drug's pharmacokinetic properties, concentrating on the volume of distribution derived from its hydrophilic and hydrophobic properties and their relationship to body composition. Estimates of Actual Body Weight (ABW) to Ideal Body Weight (IBW) compared and, ABW estimates were calculated using both UK Resuscitation Council and APLS formulae. Hydrophobic drugs have a higher volume of distribution than hydrophilic drugs as they distribute preferentially to Fat Mass (FM). The larger the volume of distribution, the higher the initial dose required to achieve therapeutic plasma concentrations. ABW estimates are a good indicator of volume of distribution for hydrophobic drugs as it correlates well with FM. IBW estimates may be a better indicator of volume of distribution than ABW for hydrophilic drugs, as it correlates better with Lean Body Mass. This highlights potential variation between ABW and IBW which may result in toxic or sub-therapeutic dosing. Abstract G303(P) Table 1 Hydrophilic Amphiphilic Hydrophobic Adrenaline Amiodarone Atropine Sodium Bicarbonate Verapamil Calcium Gluconate Lidocaine Isoprenaline Diazepam Flecanide Midazolam Adenosine Lorazepam Salbutamol Phenytoin Magnesium Sulphate Thiopentone Aminophylline Benzyl penicillin Ceftriaxone Paracetamol Sodium Nitroprusside Prednisolone Morphine Hydrocortisone Suxamethonium Dexamethasone Chlorpheniramine Ketamine Mannitol Furosemide Labetalol Epoprostenol Digoxin Results The new APLS formulae, gives higher estimates of expected weight for a wider age range. This may be a more accurate reflection of ABW, than the UK Resuscitation Council, due to an increasing prevalence of obesity in children. The UK Resuscitation Council's formula appears to result in a lower estimate of weight, which may relate more closely to IBW than ABW. Abstract G303(P) Figure 1 Abstract G303(P) Table 2 Age UK Resuscitation CouncilWeight (kg) = 2 × (age in years + 4)(For ages 1 year-10 years) APLS formulae1-12 months Weight (kg) = (0.5 × age in months) + 41-5 years Weight (kg) = (2 × age in years) + 86-12 years Weight (kg) = (3 × age in years) + 7(For ages 1 month-12 year) 1 months - 4.5 6 months - 7 11 months - 9.5 1 year 10 10 2 years 12 12 3 years 14 14 4 years 16 16 5 years 18 18 6 years 20 25 7 years 22 28 8 years 24 31 9 years 26 34 10 years 28 37 11 years - 40 12 years - 43 Conclusion The main drugs used in paediatric resuscitation are hydrophilic, thus the APLS formulae may result in too much being given. Therefore the UK Resuscitation Council's single formula may be preferred. In addition the single fo...

Comparing the usability of paediatric weight estimation methods: a simulation study

“…Many studies have examined the predicted accuracy of estimation methods against a population’s true weight with no consensus of the ideal method,6 but few studies have examined their practical application in real-world settings. Age-based calculations tend to underestimate true weight but instead predict an ideal bodyweight which, due to the pharmacological properties of most resuscitation drugs, may be more suitable 7. The only other study comparable to ours applied both age and length-based methods to a cohort of 80 children in the USA, and found a 5% error of application rate, with device-based methods (eg, tapes) having the highest rate of application errors (25%) 8…”

The utility of pediatric age‐based weight estimation formulas for emergency drug dose calculations in obese children

“…The old and the new APLS formulas were selected because they have previously been postulated to be appropriate for estimating ideal body weight in obese children. 5,10 This was because these formulas approximated the 50th centile of weight-for-age, or the "ideal" child.…”

“…Because many drugs used in the resuscitation room are hydrophilic, it is essential that the emergency physician has an approach to manage emergency drug dosing in obese children. 5 Furthermore, because the use of age-based formulas is still common-despite an increasing body of evidence against themit was important to clarify whether they could potentially have a secondary role in the prediction of ideal body weight.…”

“…4 Some authors have suggested that some age-based formulas can predict ideal body weight accurately and, on that basis, are appropriate for emergency drug dose calculations in an emergency. 2,5 The relationship between these age-based formulas and ideal body weight has never been formally evaluated. Most of the existing dose scaling methods recommended for determining ideal body weight in obese children are tedious and complex to use.…”

Estimación del peso según la edad. Comparación de las fórmulas en una muestra peruana

“…Cuando se estima el peso del niño, el grado de error que es clínicamente aceptable, es difícil de definir, esto conlleva a que las fórmulas de estimación no estén exentas de discusión debido a que la magnitud del error aumenta con la edad, talla, hábitos, crecimiento puberal, etnia, etc. Considerar incluso que la constitución propia de la masa adiposa y masa libre de grasa es muy variable entre los niños y es difícil conocer estos datos; dos niños pueden tener la misma estimación del peso, pero diferencias sustanciales en las proporciones o la masa adiposa y la masa de cuerpo delgado 4 . Estas alteraciones y excesos que son comunes en niños obesos pueden modificar los datos de estimación y no ofrecer un valor real del peso al utilizar una fórmula de estimación 33,34 .…”