There are several important issues that the physician and the elderly patient must consider. Many elderly individuals are already taking multiple medications for chronic conditions including heart disease, diabetes, hypertension, high cholesterol, etc. Therefore, it is important for the treatment team to be aware of all medications a patient is taking and to be on the lookout for specific interactions between psychiatric drugs and the medications a patient may be taking for other conditions. Information about drug interactions is readily available to physicians online and in pharmacology textbooks.

Other important considerations in elderly patients involve pharmacokinetic and pharmacodynamic changes that occur with aging. What do these two terms mean and why are they important?

Pharmacokinetics is a term that describes how our bodies handle drugs. Some pharmacokinetic factors include the absorption of a drug from the gastrointestinal (GI) system; the chemical changes the drug undergoes as it passes from the GI system through the liver into the bloodstream (this effect on the drug by the liver is known as the "first pass effect"); the distribution of the drug throughout the body; subsequent chemical changes of the drug in specific organs; and the method of eliminating the drug from the body, often by the kidneys. As people age, their livers and kidneys are less efficient at processing and getting rid of drugs. The degree to which this age-related inefficiency influences the handling of a drug is specific to individual drugs. Diazepam (Valium) is much more strongly influenced by aging of the liver than is lorazepam (Ativan), for instance. This difference between diazepam and lorazepam reflects the fact that each requires different chemical processing in the liver and age has less influence on the processing necessary for lorazepam than on the processing necessary for diazepam. As the liver and kidneys age and become less efficient, drug levels may rise in the bloodstream unless the dose is adjusted. For example, if a person with bipolar disorder is taking lithium, he or she will likely reach the same blood level on a much lower dose at age 80 than at age 40. What does this mean? It means that doctors must know (or know where to look up) the age-related pharmacokinetic changes of each drug a person is taking in order to make certain that the dosing is adjusted appropriately for age.

What about that other term - pharmacodynamic changes? This term deals with how a person responds to a drug and how drug responses may change with age. For instance, an older person may be much more sensitive to the effects of diazepam (Valium) even after adjusting the dose so that the same amount of drug is present in the brain (i.e., after correcting for pharmacokinetic changes). This increased sensitivity may result in an increased risk of side effects, for example, an increased risk of falls or confusion. Interestingly, age does not cause increased sensitivity to all drugs. What does this mean? It means that doctors must be familiar with pharmacodynamic changes that occur with aging in order to prescribe both the safest drug and the safest dose of that drug.

Certain psychiatric drugs interact with many other drugs, while other psychiatric drugs interact very little, if at all, with other drugs. By interact, we mean that one drug can result in slower or faster removal of other drugs. Therefore, certain psychiatric drugs may cause some drugs to accumulate at higher levels in the body, possibly leading to unintended side effects, and may cause other drugs to decrease in levels, possibly resulting in decreased effectiveness. What does this mean? It means that doctors must be aware of drug interactions that may occur and the nature of these interactions.

These are only a few important considerations when medications are prescribed in the elderly. The take home message is that doctors must weigh these considerations carefully when they work with patients to develop effective and safe treatment plans. In older patients, the risks of medications may be higher, and therefore, the decision to recommend specific medications may be different in older people. Many doctors who specialize in caring for the elderly are familiar with the saying "start low, go slow, but build up to a therapeutic dose." It is also important for the elderly patient and the health care team to stay in close contact whenever medications are changed. In addition, the patient or their loved ones should let each healthcare provider know about all medications that the patient is taking, including over-the-counter medications.

If this sounds complex, that is because it is complex. Medical subspecialties such as geriatric medicine and geriatric psychiatry were created to help doctors and patients navigate these complexities. These issues are yet another reason that we feel strongly that medications should only be prescribed by physicians or healthcare providers who are directly supervised by physicians.

This post was co-written by Eugene Rubin MD, PhD and Charles Zorumski MD.