Variability in Response to Medicines in Older People: Phenotypic and Genotypic Factors

Understanding the causes and consequences of variability in responses to medicines is a foundation of rational therapeutics. This relies on a detailed understanding of the pharmacokinetic and pharmacodynamic characteristics of medicines and the factors that influence them in patients.(1) Ultimately the optimal dose regimen is determined by the pharmacological phenotype of the patient, which is a consequence of the person's genes and the environment in which they are expressed.(1) Older people display considerable variability in responses to medicines, and this makes dose selection a complex process.(2,3) Pharmacogenomic factors play some part in this variability, but other clinical factors also determine an older person's phenotypic response to a medicine.(1-4) In this article we conclude that with older age, genotype plays an increasingly small role in determining a person's phenotypic response to a medicine.