What physiological factor affects pharmacokinetics in older adults?

The correct answer highlights that the function of organs slows down in older adults, which significantly affects pharmacokinetics. As individuals age, physiological changes occur that can alter the absorption, distribution, metabolism, and excretion of medications. For example, liver and kidney functions may decline, leading to reduced clearance of drugs from the body. This impaired organ function can result in higher serum concentrations of medications, increasing the risk of toxicity and adverse effects.

In contrast, the other options do not accurately represent the common physiological changes seen in older adults. For instance, metabolism of drugs tends to decrease with age, not increase. Additionally, with aging, there is often a decrease in muscle mass and an increase in body fat, which can influence how drugs are distributed in the body but does not present a direct risk of increased toxicity as highlighted in the correct answer. Furthermore, hydration levels can vary widely with age, but it is not a consistent physiological factor that would universally affect pharmacokinetics in older adults. Thus, the diminished function of organs is a crucial factor in understanding how medications can be managed safely in geriatric patients.