Children Are Not Small Adults: One Dose Doesn’t Fit All

One dosage is insufficient for children, who are not miniature adults. The phrase "children are not small adults" is essential to paediatrics, particularly when it comes to medication dosage. Because of the numerous physiological and developmental differences between children and adults, it is incorrect and possibly dangerous to directly scale up adult medicine dosages.

Principal Causes of One Dose Not Fitting All

The processes involved in drug absorption, distribution, metabolism, and excretion (ADME) are not just miniature representations of adult physiology.  Growth and maturation alter these systems, resulting in nonlinear correlations between body size and the body's ability to digest medicines. Drug metabolism and excretion are impacted by the liver and kidneys' immature state in children, particularly in neonates and infants. As an example, throughout the first six to eight months of life, renal function matures. Additionally, immature organs may hamper drug clearance, requiring lower doses or longer dosing intervals. Compared to adults, children have distinct ratios of muscle, fat, and water in their bodies. For example, infants may need larger dosages of water-soluble medications to reach therapeutic concentrations due to their increased body water content. Infants' lower plasma protein concentrations can change how drugs are distributed, resulting in different peak concentrations and effects than those of adults. Enzymes that break down drugs, like CYP450 isoenzymes, mature at varying rates. Children may remove some medications more quickly or more slowly, necessitating dose modifications. In fact, because of their greater metabolic rates, children between the ages of two and ten may require dosages of some medications that are up to 50% higher than those of adults. Drug response and safety can be greatly impacted by genetics and developmental stage, which makes dose recommendations even more difficult. 

The Drawbacks of Linear Dose Scaling

Many people believe that a child should simply take less medication based on their weight if an adult takes a particular dosage. A 4-kg infant, for instance, might be given a dose that is 1/20 times that of an adult 80-kg individual. However, this reasoning disregards children's distinct and evolving physiology. Drug absorption, distribution, metabolism, and excretion are all impacted by their unique and ever-changing organs, enzymes, and body makeup. Despite the fact that paediatric dosages are frequently determined by kilogramme or body surface area, under- or over-dosing might result from linear scaling, such as administering a 4 kg kid 1/20th the dose of 80kg adult. Children may require lower dosages of some medications because of slower metabolism or excretion, while others require larger weight-adjusted doses to reach therapeutic levels. Although allometric scaling and other empirical scaling techniques are employed, they have drawbacks and could not always accurately forecast the dosage.

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Real Life Examples

Paracetamol: One frequent medication used to treat pain and fever is paracetamol. The World Health Organisation (WHO) states that 3 grams is the recommended daily dosage (DDD) for adults. However, the weight-based suggested dosage for kids is 15 mg/kg, four times a day. A 1-year-old child weighing roughly 10 kg would require 600 mg per day, which is only 20% of the adult DDD. The daily dosage for a 16-year-old teen may reach 3.5–4 grams, which is actually more than the adult DDD. This demonstrates that there is a nonlinear relationship between dose, weight, and age. Toxicology or inefficient treatment may result from administering too much or too little.

Phenoxymethylpenicillin: Antibiotic dosages, such as that of phenoxymethylpenicillin, also differ significantly: The dosage for a 1-year-old with tonsillitis is roughly 20% of the adult dosage. The dosage for a 16-year-old may be higher than that for an adult, particularly for diseases like otitis (ear infection), when the dosage is double that of tonsillitis. We run the risk of underdosing or overdosing if we merely scaled the dose by weight, which could have negative consequences. 

Grey Baby Syndrome: Grey baby syndrome, occurs when newborns are given the antibiotic chloramphenicol at dosages meant for older children or adults, is a terrible example from medical history. The inability of newborns' livers to metabolise drugs effectively can result in toxic accumulation, heart failure, and death.

How Do Physicians and Pharmacists Get It Accurate?

To determine the appropriate dosage, paediatricians employ a number of techniques:

• By weight (mg/kg)

• By body surface area (BSA), especially for chemotherapy

• By age group, since organ maturity and drug metabolism change over time

They also take into account the child's health, organ function, and the characteristics of the particular medicine. Personalised medicine and precision dosing are being utilised more and more to further customise treatment. 

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Some formulas are used to calculate the dose for paediatric patients that are:

When it comes to managing medications for children, pharmacists are essential. By addressing the particular hazards connected to organ immaturity and developmental variability in children, their proficiency in dosage, education, monitoring, and error prevention guarantees that kids receive the safest and most efficient treatment available.

Risks Associated with Giving Children Adult Drug Doses Without Modifications

Because of the basic physiological differences between children and adults, giving adult medicine doses to children without making the appropriate changes carries serious hazards. The following are the main risks and practical adverse effects:

Conclusion

Without the right modifications, giving children adult dosages of medications can have serious, even deadly, consequences. Children and adults have different physiological characteristics, and factors such as age, weight, organ maturity, body composition, and heredity affect how they react to drugs. As a result, medicine dosage for children needs to be customised rather than merely reduced from adult dosages. This customised strategy reduces the possibility of toxicity or subtherapeutic dose while optimising therapeutic efficacy. A healthcare provider should always be consulted before administering any medication to a child.

References:

1. Factors and Mechanisms for Pharmacokinetic Differences between Pediatric Population and Adults

2. Pediatric Pharmacokinetics Refresher for Pharmacists

3. WHO Model List of Essential Medicines for Children - 8th list, 2021

4. Paediatric pharmacokinetics: key considerations

5. How and when to take phenoxymethylpenicillin

6. Paracetamol: updated dosing for children to be introduced