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THE MERCK MANUAL MEDICAL LIBRARY: The Merck Manual of Diagnosis and Therapy
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Adherence to a Drug Regimen

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Adherence (compliance) is the degree to which a patient follows a treatment regimen. For drugs, adherence requires that the prescription be obtained promptly and the drug be taken as prescribed in terms of dose, dosing interval, and duration of treatment. Patients should be told that if they stop or alter the way they take a drug, they should alert their physician, but they rarely do so.

Only about ½ of patients who leave a physician's office with a prescription take the drug as directed. The most common reasons for nonadherence are frequent dosing, denial of illness, poor comprehension of the benefits of taking the drug, and cost. Many other reasons contribute to nonadherence (see Table 1: Concepts in Pharmacotherapy: Causes of NonadherenceTables).

Table 1

Causes of Nonadherence

Source

Cause

Patient

Apathy

Concern about taking drugs (eg, adverse effects, addiction)

Denial of the disorder or its significance

Financial concerns

Forgetfulness

Misunderstanding of prescribing instructions

No faith in the drug's efficacy

Physical difficulties (eg, with swallowing tablets or capsules, opening bottles, or getting prescriptions filled)

Reduction, fluctuation, or disappearance of symptoms

Drug

Adverse effects (real or imagined)

Complex regimen (eg, frequent dosing, many drugs)

Inconvenient or restrictive precautions (eg, no alcohol or cheese)

Similar appearance of drugs

Unpleasant taste or smell

Children are less likely than adults to follow a treatment regimen. Adherence is worst with chronic disorders requiring complex, long-term treatment (eg, juvenile diabetes, asthma). Parents may not clearly understand prescription instructions and, within 15 min, forget about 12 the information given by the physician.

The elderly follow treatment regimens as well as other adults. However, factors that decrease adherence (eg, inadequate finances, use of multiple drugs or drugs that must be taken several times a day) are more common among the elderly. Cognitive impairment may further decrease adherence. Sometimes a prescriber must be creative, picking a drug that is easier to use, even if otherwise it may not be the first choice. For example, some antihypertensives (eg, clonidine Some Trade Names
CATAPRES
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) may be given by a patch that can be replaced by a visiting nurse or a family member.

The most obvious result of nonadherence is that the disorder may not be relieved or cured. Nonadherence is estimated to result in 125,000 deaths due to cardiovascular disorders each year in the US. If patients took their drugs as directed, up to 23% of nursing home admissions, 10% of hospital admissions, many physician visits, many diagnostic tests, and many unnecessary treatments could be avoided.

Pharmacists and nurses may detect and help solve adherence problems. For example, a pharmacist may note that a patient does not obtain refills or that a prescription is being refilled too soon. In reviewing prescription directions with the patient, a pharmacist or nurse may uncover a patient's misunderstandings or fears and alleviate them. Doctors can alter complicated or frequent dosing or substitute safe, effective, but less expensive drugs. Communication among all health care practitioners that provide care for a patient is important.

Last full review/revision November 2005

Content last modified November 2005

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