Pharmacokinetics in Geriatric Patients: Effect of Age on Drug Distribution

Aging affects drug distribution mainly through changes in plasma protein concentration and body composition.

Older individuals usually have decreased albumin levels and increased α1-acid glycoprotein levels.

As a result, drugs with narrow therapeutic indices, like lidocaine and highly protein-bound drugs like warfarin, require dosing regimen adjustments to reduce toxicity risks.

Aging also leads to decreased lean body mass and total body water. This reduces the distribution volume for hydrophilic drugs like digoxin, theophylline, and aminoglycosides.

Conversely, body fat increases with age. This can potentially increase the volume of distribution for lipophilic drugs like benzodiazepines, resulting in lower plasma drug concentrations for equivalent doses.