Medication and the Aged

June 30, 2008

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One of the problem with many drugs that are on the market is they were only tested on a certain population. It used to be that drugs were basically tested on white males in their middle years. Now there is much more testing on women but there is still not much testing on the aged. Why does being elderly make a difference? Here are two of the reasons.

As we age there are a range of changes in our bodies. This has implications for the medications we take. One of these is that the relative amount of fluid in our bodies decreases. Most drugs are not evenly distributed throughout the body, but are found either predominantly in either in fluid or in fat. The majority of drugs are in fluids, which includes blood, inside cells, between cells etc.

For a drug that is found in fluids, if the amount of fluid in the body is less, then for the same dose the concentration of the drug will be higher. Same amount in a smaller volume. This can mean that for the same dose the concentration of the drug in the body can be higher.

Additionally, some processes in the body slow down, whereas others do not. There are a range of mechanisms for clearing medications from the body (that’s why we have to keep taking them). Different drugs are cleared by different mechanisms. If one of these mechanisms is slower or does not work as well, for the same dose there will be drug may build up in the body.

Drugs have what is known as a therapeutic window. Below a certain concentration in the body, they have little or no effect. Above a certain concentration in the body, there will start to be serious side effects. Different drugs have different sized windows. If a drug has a narrow window, then an increase in concentration in the body can have serious consequences.

The bottom line is that a drug that works and is well tolerated in a younger person may or may not be suitable for an elderly person. This problem is compounded by the fact that as we age, we usually need to take many more medications. Many physicians do not fully consider the age of the person once they have reached adulthood. If you are involved in the care of any elderly persons, having them see a physician who specializes in gerontology may be helpful for quality of life, including less side effects and potential medication problems.

photo credit: peyri