Why might therapeutic doses of certain medications become toxic in older individuals?

Therapeutic doses of certain medications can become toxic in older individuals primarily due to the deterioration of the liver. The liver is crucial for the metabolism of many drugs, as it breaks down medications into metabolites that can be more easily eliminated from the body. As individuals age, liver function can decline due to factors such as reduced hepatic blood flow, decreased enzyme activity, and potential liver diseases associated with age. This diminished liver function can lead to a slower clearance of medications from the bloodstream, resulting in higher concentrations that can reach toxic levels even when administered at standard therapeutic doses.

In this context, while other organs such as the spleen, intestinal tract, and gallbladder may also play roles in overall health and drug metabolism indirectly, they do not have the same direct impact on the metabolism of medications as the liver does. The liver's critical role in processing drugs makes it the primary concern when considering why therapeutic doses may lead to toxicity in the elderly.