Pediatric Dose Calculations Based on Age, Body Weight and Body Surface Area

Throughout childhood and adolescence, pediatrics refers to diseases that affect children. New-borns are defined as newborns to 1 month old; infants 1 month to 1 year of age; early childhood is defined as 1 up to 5 years; late childhood is defined as 6 through 12 years, and adolescents are classified as 13-17 years of age 1.

During the first month after birth, infants are considered neonates.

One who is between one month and one year old.

The adolescent stage encompasses the ages of 13 and 17.

Children's dosage depends on factors such as their age and weight, their health status, their respiratory system, and the stage of development of their body systems for drugs metabolism (e.g., liver enzymes) and elimination (e.g., kidneys). Newborns are not capable of fully developing these biological functions and systems. It begins during the second year of life that the nervous and renal systems are developed. Antimicrobial agents are frequently introduced to newborns, infants, and young children, who mainly excrete them through their kidneys. Because antibiotics are the most commonly prescribed drugs in these populations, this is especially relevant in this case. Drugs can accumulate in the body and cause overdose and toxicity if the rate of drug elimination is not considered properly.

When dealing with pediatric patients as well as adults, body weight plays a key role in dose calculation. The safe pediatric dose is calculated by two different methods. The calculation is measured in milligrams or micrograms per kilogram based on body weight or in square meters and based on body surface area (BSA). Chemotherapeutic agents are often measured by the BSA method since it is more accurate. Milligrams per kilogram is what it is called in most other places. A microgram per kilogram dose may be used for medications given in small amounts.

Rules-based on age

Age was used as the foundation of the first rules. Augustsberger pointed out that Dilling's rule (age/20) dates back to the 8th century. Age/20, (4age)20, and age/(age12) is the most commonly used in figure 1, plotted using ages weighted by the standard tables. Age determines weight considerably (between the 3rd and 97th percentiles); it was 25 percent to 20 percent at 10 kg at 1 year, and it was 45 to 26 percent at 40 kg at 13 years. This leads to a very unreliable set of rules. The BSA curve for normal-sized children is best fitted to the weight (age) 20 estimate if weight is unavailable.

Rules-based on weight

The first weight proportional regimen for drug therapy, according to Professor A.J. Clark of Edinburgh, was established in 1861. His first rule was: the fraction of an adult dose equal to the weight (lb) per 150 grams. Augsberger made this method more accurate by substituting multiplication for division and adding ten, resulting in: ((1.5wt (kg))10) percent of an adult dose. In practice, this rule is not quoted widely because it is difficult to calculate. At 60 kg, it reaches 100%, which is the best fit to the BSA curve that can be made.



Despite its disadvantages, mg kg dosages have been very popular due to their attractive simplicity.

1. Using it effectively requires knowledge of diverse dosages of drugs (n mg kg), as well as different doses for different ages;
2. The mathematics in the bedside rule may not be as straightforward, adding tenths, hundredths, or hundredths of an mg kg may result in the decimal point being misplaced;
3. Since it does not relate immediately to adult doses, it is not obvious when maligned prescriptions are written;
4. As that varies between approximately 45% at 15 kg to 20% at 40 kg when compared with the BSA graph, assays of drug concentrations show that its use "under doses" for much of its range.

Rules-based on body surface area

A device's surface area is strongly recommended for drug dosage calculations because the rate of metabolism or redistribution of drugs is proportional to its metabolic rate, which in turn reflects the amount of heat that is lost, which in turn correlates with warm objects' surface area. Assays of blood concentrations of drugs and measurements of organ dimensions and volumes correlate well with BSA.

Get subject wise printable pdf documentsView Here