Which type of medication will have a larger volume of distribution in elderly patients with reduced total body water?

Lipid-soluble medications tend to have a larger volume of distribution in elderly patients, particularly those with reduced total body water. This is primarily due to the way drugs distribute within the body compartments. Lipid-soluble medications can easily cross cell membranes and tend to accumulate in fatty tissues, which generally makes their volume of distribution larger than that of water-soluble drugs.

In elderly patients, the reduction in total body water can lead to a relatively higher concentration of water-soluble medications within the plasma compartment compared to their distribution in body tissues. Consequently, while water-soluble medications may have a smaller volume of distribution due to the decreased water in the body, lipid-soluble medications may distribute more widely due to their preference for adipose (fat) tissue, which does not decrease in proportionate size as significantly in the elderly.

This physiological change underscores the importance of monitoring and adjusting dosages of medications based on the patient's age and body composition, specifically considering how these factors affect the pharmacokinetics of various drugs.