**14.14. Drug distribution**

In geriatrics the 'body mass' declines with age and the total body water content falls by between 10 – 15%. The volume of distribution of hydrophilic drugs will therefore decrease while plasma concentration will increase and the likelihood of toxic drug effects will also increase. When geriatric patients use diuretics, the extracellular space reduces even further leading to a higher likelihood of drug toxicity. The total body fat in the elderly increases by 12 – 18%, therefore, for hydrophobic drugs, the higher volume of distribution implies an increase in half life of distribution and the time needed to reach steady-state serum concentration. Therefore, for geriatrics a once or twice daily drug administration is optimal. This can be achieved though delayed release or fixed drug combinations.
