Copyright © 2013, 2010 by Saunders, an imprint of Elsevier Inc.

Chapter 11

Drug Therapy in Geriatric Patients

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Geriatric Patients

Disproportionately high prescription drug use exists in the elderly. 12% of Americans are age 65 years or older. This 12% consumes 31% of prescribed drugs.

Geriatric patients experience more adverse drug reactions and drug-drug interactions than younger patients do.

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Geriatric Patients

Altered pharmacokinetics More sensitive to drugs than younger adults and

have wider variation Multiple and severe illnesses

Severity of illness, multiple pathologies Multiple-drug therapy

Excessive prescribing Poor adherence

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Geriatric Patients

Individualization of treatment is essential. Each patient must be monitored for desired

and adverse responses. Regimen must be adhered to. Goal of treatment

Reduce symptoms and improve quality of life.• Cure is generally impossible.

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Outline of Drug Therapy in Geriatric Patients

Pharmacokinetic changes in the elderly Pharmacodynamic changes in the elderly Adverse drug reactions and drug interactions Promoting adherence

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Pharmacokinetics: Absorption

Altered GI absorption is not a major factor in drug sensitivity.

Percentage of an oral dose that is absorbed does not change with age.

Rate of absorption may slow. Delayed gastric emptying and reduced

splanchnic blood flow occur.

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Pharmacokinetics: Distribution

Increased percentage of body fat Storage depot for lipid-soluble drugs

Decreased percentage of lean body mass Decreased total body water

Distributed in smaller volume; thus concentration is increased and effects are more intense

Reduced concentration of serum albumin May be significantly reduced in the malnourished Causes decreased protein binding of drugs and

increase in levels of free drugs

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Pharmacokinetics: Metabolism

Hepatic metabolism declines with age. Reduced hepatic blood flow, reduced liver

mass, and decreased activity of some hepatic enzymes occur.

Half-life of some drugs may increase, and responses are prolonged.

Responses to oral drugs (those that undergo extensive first-pass effect) may be enhanced.

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Pharmacokinetics: Excretion

Renal function undergoes progressive decline beginning in early adulthood. Reductions in renal blood flow, glomerular filtration

rate (GFR), active tubular secretion, and number of nephrons

Drug accumulation secondary to reduced renal excretion is the most important cause of adverse drug reactions in the elderly.

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Pharmacokinetics: Excretion

Renal function should be assessed with drugs that are eliminated primarily by the kidneys.

In elderly patients Use creatinine clearance, not serum creatinine,

because lean muscle mass (source of creatinine) declines in parallel with kidney function.

Creatinine levels may be normal even though kidney function is greatly reduced.

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Pharmacodynamic Changes in the Elderly

Alterations in receptor properties may underlie altered sensitivity to some drugs. Drugs with more intense effects in the elderly

• Warfarin, certain CNS depressants Beta blockers less effective in the elderly, even in

the same concentrations • Reduction in number of beta receptors • Reduction in the affinity of beta receptors for beta

receptor blocking agents

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Adverse Drug Reactions

Seven times more likely in the elderly Account for 16% of hospital admissions Account for 50% of all medication-related

deaths Majority are dose related, not idiosyncratic Symptoms in elderly often nonspecific

Dizziness, cognitive impairment

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Predisposing ADR Factors

Drug accumulation secondary to reduced renal function

Polypharmacy Greater severity of illness Multiple pathologies Greater use of drugs that have a low therapeutic

index (eg, digoxin) Increased individual variation secondary to altered

pharmacokinetics Inadequate supervision of long-term therapy Poor patient adherence

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Measures to Reduce ADRs

Take thorough drug history, including OTCs. Consider pharmacokinetic and pharmacodynamic

changes due to age. Monitor clinical response/plasma drug levels. Use the simplest regimen possible. Monitor for drug-drug interactions. Periodically review the need for continued drug

therapy. Encourage patient to dispose of old meds. Take steps to promote adherence and avoid drugs on

the Beers list.

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Promoting Adherence with Unintentional Nonadherence

Simplified drug regimens Clear, concise verbal and written instructions Appropriate dosage form Clearly labeled and easy-to-open containers Daily reminders Support system Frequent monitoring

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Intentional Nonadherence

Most cases (75%) of nonadherence are intentional.

Reasons include Expense, side effects, patient’s conviction that the

drug is unnecessary or the dosage is too high