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Medication Errors
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Background and definitions

Prescription medication use is widespread, complex, and increasingly risky. Clinicians have access to an armamentarium of more than 10,000 prescription medications, and nearly one-third of adults in the United States take 5 or more medications. Advances in clinical therapeutics have undoubtedly resulted in major improvements in health for patients with many diseases, but these benefits have also been accompanied by increased risks. An adverse drug event (ADE) is defined as harm experienced by a patient as a result of exposure to a medication, and ADEs account for nearly 700,000 emergency department visits and 100,000 hospitalizations each year. ADEs affect nearly 5% of hospitalized patients, making them one of the most common types of inpatient errors; ambulatory patients may experience ADEs at even higher rates. Transitions in care are also a well-documented source of preventable harm related to medications.

As with the more general term adverse event, the occurrence of an ADE does not necessarily indicate an error or poor quality care. A medication error refers to an error (of commission or omission) at any step along the pathway that begins when a clinician prescribes a medication and ends when the patient actually receives the medication. Preventable adverse drug events result from a medication error that reaches the patient and causes any degree of harm. It is generally estimated that about half of ADEs are preventable. Medication errors that do not cause any harm—either because they are intercepted before reaching the patient, or by luck—are often called potential ADEs. An ameliorable ADE is one in which the patient experienced harm from a medication that, while not completely preventable, could have been mitigated. Finally, a certain percentage of patients will experience ADEs even when medications are prescribed and administered appropriately; these are considered adverse drug reactions or non-preventable ADEs (and are popularly known as side effects).

For example, the intravenous anticoagulant heparin is considered one of the highest-risk medications used in the inpatient setting. Safe use of heparin requires weight-based dosing and frequent monitoring of tests of the blood's clotting ability, in order to avoid either bleeding complications (if the dose is too high) or clotting risks (if the dose is inadequate). If a clinician prescribes an incorrect dose of heparin, that would be considered a medication error (even if a pharmacist detected the mistake before the dose was dispensed). If the incorrect dose was dispensed and administered, but no clinical consequences occurred, that would be a potential ADE. If an excessively large dose was administered and was detected by abnormal lab results, but the patient experienced a bleeding complication due to clinicians failing to respond appropriately, it would be considered an ameliorable ADE (that is, earlier detection could have reduced the level of harm the patient experienced).

Risk factors for adverse drug events

There are patient-specific and drug-specific risk factors for ADEs. Polypharmacy—taking more medications than clinically indicated—is likely the strongest risk factor for ADEs. Elderly patients, who take more medications and are more vulnerable to specific medication adverse effects, are particularly vulnerable to ADEs. Pediatric patients are also at elevated risk, particularly when hospitalized, since many medications for children must be dosed according to their weight. Other well-documented patient-specific risk factors include limited health literacy and numeracy (the ability to use arithmetic operations for daily tasks), both of which are independently associated with ADE risk. It is important to note that in ambulatory care, patient-level risk factors are probably an under-recognized source of ADEs. Studies have shown that both caregivers (including parents of sick children) and patients themselves commit medication administration errors at surprisingly high rates.

The Institute for Safe Medication Practices maintains a list of high-alert medications—medications that can cause significant patient harm if used in error. These include medications that have dangerous adverse effects, but also include look-alike, sound-alike medications, which have similar names and physical appearance but completely different pharmaceutical properties. The Beers criteria, which define certain classes of medications as potentially inappropriate for geriatric patients, have traditionally been used to assess medication safety. However, the newer STOPP criteria (Screening Tool of older Person's inappropriate Prescriptions) have been shown to more accurately predict ADEs than the Beers criteria, and are therefore likely a better measure of prescribing safety in the elderly.

Though there are specific types of medications for which the harm generally outweighs the benefits, such as benzodiazepine sedatives in elderly patients, it is now clear that most ADEs are caused by commonly used medications that have risks, but offer significant benefits if used properly. These medications include antidiabetic agents (e.g., insulin), oral anticoagulants (e.g., warfarin), and antiplatelet agents (such as aspirin and clopidogrel). Together, these four medications—which are not considered inappropriate by the Beers criteria—account for nearly 50% of emergency department visits for ADEs in Medicare patients. Focusing on improving prescribing safety for these necessary but higher-risk medications may reduce the large burden of ADEs in the elderly to a greater extent than focusing on use of potentially inappropriate classes of medications.

Prevention of adverse drug events

The pathway between a clinician's decision to prescribe a medication and the patient actually receiving the medication consists of several steps:

  • Ordering: the clinician must select the appropriate medication and the dose and frequency at which it is to be administered.
  • Transcribing: in a paper-based system, an intermediary (a clerk in the hospital setting, or a pharmacist or pharmacy technician in the outpatient setting) must read and interpret the prescription correctly.
  • Dispensing: the pharmacist must check for drug–drug interactions and allergies, then release the appropriate quantity of the medication in the correct form.
  • Administration: the correct medication must be supplied to the correct patient at the correct time. In the hospital, this is generally a nurse's responsibility, but in ambulatory care this is the responsibility of patients or caregivers.

While the majority of errors likely occur at the prescribing and transcribing stages, medication administration errors are also quite common in both inpatient and outpatient settings. Preventing medication errors requires specific steps to ensure safety at each stage of the pathway (Table).

Table. Strategies to prevent adverse drug events

  • Clinical pharmacists to oversee medication dispensing process
  • Use of "tall man" lettering and other strategies to minimize confusion between look-alike, sound-alike medications

Although each of the strategies enumerated in the Table can prevent ADEs when used individually, fundamentally, improving medication safety cannot be divorced from the overall goal of reducing preventable harm from all causes. Analysis of serious medication errors invariably reveals other underlying system flaws, such as human factors engineering issues and impaired safety culture, that allowed individual prescribing or administration errors to reach the patient and cause serious harm. Integration of information technology solutions (including computerized provider order entry and barcode medication administration) into "closed-loop" medication systems holds great promise for improving medication safety in hospitals, but the potential for error will remain unless these systems are carefully implemented and these larger issues are addressed.

Current Context

Preventing ADEs is a major priority for accrediting and regulatory agencies. The Joint Commission has named improving medication safety as a National Patient Safety Goal for both hospitals and ambulatory clinics, and more recently, the Partnership for Patients has included ADE prevention as one of its key goals for improving patient safety. The Partnership for Patients has set a goal of reducing preventable ADEs in hospitalized patients by 50% by 2013, estimating that more than 800,000 ADEs could be prevented if this goal is met.

What's New in Medication Errors on AHRQ PSNet
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My Medicines.
Silver Spring, MD: US Food and Drug Administration. Office of Women's Health and National Association of Chain Drug Stores.
Pharmacists in pharmacovigilance: can increased diagnostic opportunity in community settings translate to better vigilance?
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Unrealized potential and residual consequences of electronic prescribing on pharmacy workflow in the outpatient pharmacy.
Nanji KC, Rothschild JM, Boehne JJ, Keohane CA, Ash JS, Poon EG. J Am Med Inform Assoc. 2014;21:481-486.
Editor's Picks for Medication Errors
From AHRQ WebM&M
Medication Overdose.
Rainu Kaushal, MD, MPH. AHRQ WebM&M [serial online]. April 2003
40 of K.
Timothy S. Lesar, PharmD. AHRQ WebM&M [serial online]. November 2003
Bad Writing, Wrong Medication.
Beth Devine, PharmD, MBA, PhD. AHRQ WebM&M [serial online]. April 2010
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Effect of bar-code technology on the safety of medication administration. Classic icon
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Adverse drug events in ambulatory care. Classic icon
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Preventing pediatric medication errors.
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Preventing Medication Errors: Quality Chasm Series. Classic icon
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Last Updated: October 2012