SECTION 1: PHARMACOKINETIC CHANGES

Pharmacokinetic changes describe how medications are absorbed, distributed, metabolized and excreted from the body.

Absorption relates to the time required for a medication to enter the general blood circulation after being introduced into the body by oral, rectal, or injectable routes. The two factors that affect absorption are the time it takes the drug to be absorbed and the amount of drug that passes through the absorbing surface into the body. Injected drugs are immediately placed into circulation. Swallowed drugs pass through the gastrointestinal system until absorption occurs; most drugs are absorbed in the small intestine. Drugs introduced rectally are absorbed through a mucous membrane into the bloodstream. Most changes in absorption are due to illness or other factors rather than aging.

Distribution relates to the transport of that medication throughout the body by way of the general blood circulation. Most drugs bind themselves to a blood protein molecule for transport.

Changes & effects related to distribution:

Metabolism relates to the biotransformation of a drug into a form that can be excreted from the body. The liver is the primary site of drug metabolism.

Changes & effects related to metabolism:

• Slower liver function relates to slower biotransformation of drugs; therefore, active drug is available longer increasing risk of toxicity.

Excretion is the process of eliminating drugs from the body. The liver, after breaking down and inactivating the drugs, either deposits them into the intestines to be removed in the feces or deposits the inactive drugs back into the bloodstream to be filtered out by the kidney and removed from the body through the urine.

Changes & effects related to excretion:

• Kidney blood flow and filtration ability has been known to decline with advancing age: Any decline in kidney function due to age or disease results in less efficient elimination of drugs. Therefore the risk of drug toxicity increases.

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SECTION 2: DRUG ACTION AND INTERACTIONS

Every drug has an affinity for specific receptor sites on specific cells. When the drug connects with that specific receptor it causes a chemical action affecting the body in a specific way. This process is called pharmacodynamics. Interference with the intended outcome of drug therapy may be precipitated by drug-drug, drug-nutrient, drug-disease interaction, and the social or psychological factors that influence drug response.

Drug Interactions: Occur when two or more medications given together or in close sequence result in an outcome different than what was intended for each particular drug. Possible reactions are drug potentiation, synergism, or antagonism. Some examples of interaction include: similar drugs can complete for binding sites on particular proteins causing a varied availability of one of the drugs; one drug may cause a physical reaction that alters absorption of the other drug; one drug may alter the metabolism of another drug causing possible drug deficiencies, or adverse and toxic responses.

The importance of knowing this information for elders is the potential impact of interactions on their activities of daily living and functional capacities such as vision, hearing, memory, and mobility. Any interference with function could have implications for injury.

Adverse Reactions: Result from interaction of medications with factors that alter drug response. Those factors include illness, nutritional and fluid states, multiple medications, and compliance with therapy. Reactions occur very frequently in elders due to the high number of drugs taken by this segment of the population. The most common adverse reactions are sedation, lethargy, and confusion. Falls frequently occur as a result of these adverse reactions. The most common drugs producing adverse reactions include anticoagulants, heart drugs, steroids, diuretics, antihypertensives, insulin, aspirin, and antidepressants (Nolan & O'Malley, 1989).

Drug Toxicity: Results from an excess of one drug in the body which exceeds the therapeutic level. The drug potentially becomes a harmful agent resulting in an adverse reaction.

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SECTION 3: PATTERS OF DRUG USE AND MISUSE

Shaughnessy (1992) suggests that the chance for an adverse reaction to occur is 6% when two drugs are taken, rises to 50% with five drugs, and to 100% when eight or more drugs are taken together.

Self-prescribing: Occurs because of the high cost of medications, not wanting to bother the physician, and the belief in and use of folk medicine and herbal remedies.

Over-The-Counter (OTC) Drugs: Medications that can be purchased without a prescription from the physician. Currently, over 300,000 products contain drug compounds deemed safe by the Food and Drug Administration (FDA) for everyone to purchase and self-administer without a physician's order. Interactions and adverse reactions with OTC drugs can occur as easily as with prescribed medications. Therefore, the importance of everyone being educated about safe medication usage is paramount.

Misuse of Drugs: Occurs for many reasons. The forms of misuse include overuse, underuse, erratic use, and contraindicated use. Most elders have minimum supervision with medications. Many lack adequate knowledge about medications. Others have sensory impairments (poor eyesight or hearing) or memory difficulty that interferes with understanding instructions, and lack an understanding of instructions due to communication difficulty with medical jargon. A person's ego plays a role in misuse by not wanting to admit to others their lack of understanding for fear of being labeled "stupid" or "a stupid old person".

Inadequate physician training in geriatric pharmacology leads to inappropriate prescribing such as by treating a symptom rather than a cause, or over-prescribing an elder with an adult dose of medication. For example, an elder with fluid accumulation in the legs (edema commonly associated with congestive heart failure) might be given a diuretic. Thorough assessment could reveal that the edema is from immobility; movement therapy would be initiated instead of prescribing medication. If, however, the physician found that the diuretic was appropriate, then initiating therapy with a smaller dose rather than the usual starting dose for adults would be appropriate.

Common sense is not always appropriate when dealing with medications. Statements such as "if some is good, more must be better" can lead to dangerous overdoses. The only common sense is to be a smart consumer or make sure you have a knowledgeable advocate to assist you.

Noncompliance is a term covering behaviors about a person's refusal or inability to follow a drug therapy regimen. It has been suggested that seventy-five percent of older adults intentionally are noncompliant; then alter the prescribed drug dose because they think the drug did not work or experienced undesirable side effects (Ebersole & Hess, 1994). "One cannot and will not comply with a prescription or treatment plan when there are incompatibilities that interfere with the practicalities of life or are distressful or disability prevents compliance" (Ebersole & Hess, 1994, p. 319).

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