Clinical Pharmacology in Special Populations
Drug handling in geriatrics and paediatrics — adherence, dosage forms and pharmacokinetics
Special populations — including older adults and children — present unique challenges in pharmacology. Physiological differences affect how drugs are absorbed, distributed, metabolised, and excreted, making standard adult dosing inappropriate or unsafe. Understanding the pharmacokinetic and practical differences in these groups is essential for safe, effective prescribing. Careful evaluation of the patient's age, weight, organ function, and ability to take medicines guides individualised treatment decisions.
Medicines in Older Adults
Non-adherence is common in older adults and arises from physiological factors (such as dysphagia, dry mouth, and cognitive decline), behavioural factors (beliefs, cost), and treatment-related factors (complex regimens, polypharmacy, lack of suitable formulations). Around 40% of adults have difficulty swallowing tablets — size being the main barrier. Choosing appropriate dosage forms, simplifying regimens, and using liquid formulations, orodispersible tablets, or transdermal patches can significantly improve adherence and outcomes in older patients.
Children Are Not Small Adults
Paediatric pharmacology is based on the principle that children are not small adults. Drug handling is non-linear and constantly changing across development — from neonates (birth to 28 days) through infants, children, and adolescents. Simple weight-based dose scaling from adult doses is inadequate and can lead to under- or over-dosing. Gastric pH, body composition, liver enzyme maturity, and kidney function all differ significantly from adults and from each other across paediatric age groups. These differences must be understood to prescribe safely in children.
Pharmacokinetic Differences in Special Populations
Absorption is affected by gastric pH differences — neonates have a neutral gastric pH unlike the acidic pH in adults, altering drug absorption. Distribution differs because neonates have higher body water and lower body fat — water-soluble drugs have a larger volume of distribution, and reduced protein binding increases free drug concentrations and toxicity risk. Metabolism is immature in neonates due to underdeveloped liver enzymes; enzyme activity increases with age, reaching adult levels around 2 to 5 years. Excretion is reduced in neonates due to low glomerular filtration rate, leading to slower drug clearance and increased toxicity risk. These ADME differences mean that drug behaviour in children must be evaluated individually based on age and development, not assumed from adult data. This article has been carefully prepared following evaluation of current pharmacokinetic and clinical pharmacology principles.