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  • Describe the age-related physiological changes to the gastrointestinal tract in older adults and pediatric patients*.

  • Describe the effects of age on drug absorption in older adults and pediatric patients.

  • Describe the effects of age on drug metabolism and disposition in older adults, pediatric patients, and obese patients.

  • Provide examples of pharmacodynamic changes in older adults and pediatric patients.

  • Describe the pharmacokinetics and pharmacodynamics changes in obese patients.

  • Describe the global prevalence of obesity and the impact of obesity on the health of an individual.

  • Classify obesity based on body mass index.

  • List the classification of the pediatric age categories.

  • Explain the differences in volume distribution in obese versus non-obese patients.

  • Describe the differences in renal elimination between obese and non-obese patients.

  • Apply pharmacokinetic principles for drug dosing in obese patients.

  • Calculate different body weight descriptors and estimate creatinine clearance for obese patients.


To ensure safe and effective therapy for special populations, an understanding of the pharmacokinetics and pharmacodynamics in those patients is essential. Earlier in the book the impact of disease states, such as renal disease or hepatic disease, on pharmacokinetics and pharmacodynamics was discussed. The focus of this chapter is to discuss the impact that special populations have on pharmacokinetics and pharmacodynamics. The populations that are discussed in this chapter are age (pediatric and older adults) and obese patients. There are additional populations that may be impacted, such as sex differences in pharmacokinetics and pharmacodynamics, but these are not addressed in this chapter. Finally, additional alterations in pharmacokinetics may occur due to renal impairment, hepatic impairment, pregnancy, various pathophysiologic conditions, and are discussed elsewhere.

*All authors contributed equally to this chapter



Aging is a complex and multifactorial process that includes functional deficits of multiple organs and tissue. The gradual decline in system function impacts the pharmacokinetics and pharmacodynamics of many drugs. However, the actual impact on drug therapy is often difficult to predict since system function often declines at varying rates with age. Given the difficulty to predict, patients are often stratified into subgroups to make drug, dosing, and frequency decisions (eg, 65–75; 75–85; and ≥85 years). Adding even more complexity, older patients usually have more disease burden and thus take multiple drug therapies. In fact, persons aged 65 and older are the most medicated group of patients and receive the highest proportion of prescription drugs. Therefore, elderly patients with a chronological age of 65 years and over have increased likelihood for underlying diseases, drug interactions, and adverse drug events (Hilmer and Gnjidic, 2009).

The age group of 65 and over is the fastest growing segment of the population in many developed countries, including the United States. In 2030, the projected number of people in the United States aged 65 ...

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