Pharmacotherapy Considerations in Elderly Adults

James M. Wooten, PharmD

Disclosures

South Med J. 2012;105(8):437-445. 

In This Article

Pharmacodynamics

Pharmacokinetics is essentially the science of how the body affects the drug and pharmacodynamics is the study of how a specific drug affects the body. All drugs have specific mechanisms of action and various adverse effects that are caused by pharmacological interactions in the body. The aging process may induce more or less sensitivity to particular medications. This is especially noteworthy for drugs that affect the cardiovascular and/or central nervous systems. This process may be caused by the effects that certain drugs have on receptor sites. As the body ages, the affinity that some medications have at particular receptor sites may change. The number of receptor sites also may change over time, which can affect the efficacy of some drugs.[1,5,15,18]

Because of the physiological aspects of aging, elderly adults also may be at high risk for certain drug adverse effects. For instance, anticholinergic/antihistamines frequently cause urinary retention. This may not be a problem for younger patients, but it may be a severe problem for older male patients with benign prostatic hypertrophy. Patients maintained on certain blood pressure medications for many years may experience sudden precipitous drops in blood pressure caused by age-induced orthostatic hypotension. These are basic adverse effects of drugs, but they are caused by age-related physiological changes.[22]

Many older patients are prone to the effects that certain drugs have on the central nervous system, including dizziness, sedation, seizures, and confusion. These effects pose problems for elderly patients, who can be extremely sensitive to any drug-induced action on the central nervous system. Other drug-induced pharmacodynamic effects manifested by aging include drug-induced renal toxicity, which can be a major issue, especially in elderly patients who are already experiencing renal problems.

The effectiveness of certain drugs that act on specific receptors may be diminished in elderly patients. [beta]-Adrenergic blockers are known to have a diminished effect in older people, probably because of a loss of sensitivity in the receptor. Proper titration of doses and patient monitoring will ensure that the correct therapy is prescribed.[18]

Predicting the extent of drug-related pharmacodynamic changes can be difficult. Because older adults can be sensitive to the pharmacological actions of drugs, care should be used whenever new medications are initiated in them. Starting with lower drug doses and titrating the dose as tolerated may help to prevent unwanted drug-related pharmacodynamic effects (Table 3). An understanding about how to properly monitor patients for a specific therapeutic response and understanding various drug-related adverse effects also may help healthcare practitioners to ensure the desired pharmacodynamic effect. As an example, consider the antihypertensive prazosin. This peripheral [alpha]-adrenergic receptor blocker effectively reduces blood pressure in most patients. A common adverse effect of prazosin in many elderly patients is first-dose syncope. Because the aging process can affect the ability of the body to recover from orthostatic changes, [alpha]-blockers are commonly associated with orthostatic hypotension and patients must be instructed to anticipate this adverse effect until they become familiar with how the drug works in their body.

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