What age-related change is responsible for slower drug clearance in older adults?

The age-related change that is responsible for slower drug clearance in older adults is decreased hepatic flow. As individuals age, there is a natural decline in liver size and hepatic blood flow, which significantly affects the metabolism of drugs processed by the liver. The liver is crucial in drug biotransformation, where it modifies substances to facilitate their elimination from the body.

When hepatic blood flow is reduced, it can result in decreased clearance of drugs that undergo first-pass metabolism, meaning that a larger proportion of the drug remains in the systemic circulation for a longer time. This change can lead to potential toxicity if dosages are not adjusted appropriately for older adults, who may already have other age-related physiological changes that affect pharmacokinetics.

The other options relate to different physiological aspects that do not directly correlate with the slower drug clearance observed in older adults. For instance, increased renal function would enhance clearance, increased body mass does not necessarily impede drug clearance specifically related to age, and decreased gastrointestinal motility primarily affects drug absorption rather than clearance. Understanding these dynamics is crucial for safe and effective medication management in older populations.