Developmental pharmacology and age-related pharmacokinetics

Quote the developmental stage before you argue the dose. Postmenstrual age, postnatal age, weight in kilograms and the maturational trajectory of the relevant organ together set the safe exposure window. [1] [5]

Overview & Definition

Developmental pharmacology is the study of how drug handling and drug action change across the developmental continuum — from fetal life, through preterm and term neonate, infancy, childhood, adolescence and into adult transition. [1] The reason it deserves its own topic is that pharmacokinetics in children is not a scaled-down version of adult pharmacokinetics. The same dose per kilogram that is curative in a teenager can be lethal in a preterm neonate, because the gut, the body water compartments, the hepatic enzymes and the kidney all mature at different rates over the first months and years of life. [1] [5]

The working definition a fellowship candidate should hold is operational. Pharmacokinetics (PK) describes what the body does to the drug — absorption, distribution, metabolism and excretion, summarised by the apparent volume of distribution (Vd), clearance (CL) and half-life (t½). Pharmacodynamics (PD) describes what the drug does to the body. In paediatrics, PK is the dominant variable that changes with age, and the change is steepest in the first month of life. [1] [4]

The age variables that matter for prescribing are gestational age at birth, postmenstrual age (gestational plus postnatal, used as the covariate for renal maturation), postnatal age, corrected age, and weight in kilograms. [5] [7] The next sections walk through how each ADME phase matures, and how that should change what you write on the chart.

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