Merck Manual

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Drug Errors


Shalini S. Lynch

, PharmD, University of California San Francisco School of Pharmacy

Reviewed/Revised May 2022 | Modified Sep 2022

Drug errors contribute to morbidity and mortality. They are estimated to cost the US health care system up to $177 billion (depending on definitions) annually. Drug errors may involve

  • The wrong choice of a drug or a prescription for the wrong dose, frequency, or duration

  • An error in reading the prescription by the pharmacist so that the wrong drug or dose is dispensed

  • An error in reading the label of the drug container by the caregiver so that the wrong drug or dose is given

  • Incorrect instructions to the patient

  • Incorrect administration by a clinician, caregiver, or patient

  • Incorrect storage of a drug by the pharmacist or patient, altering the drug’s potency

  • Use of an outdated drug, altering the drug’s potency

  • Confusion of the patient so that the drug is taken incorrectly

  • Inaccurate transmission of prescription information between different providers

Special subpopulations

Errors in prescribing are common, especially for certain populations. Older people, women of childbearing age, and children are particularly at risk. Drug interactions particularly affect people taking many drugs. To minimize risk, clinicians should know all drugs being taken—including those prescribed by others and over-the-counter drugs—and keep a complete problem list. Patients should be encouraged to write and update a list of their current drugs and dosages and bring the list to every health care appointment or emergency department visit. If there is any doubt as to which drugs are being used, patients should be instructed to bring all their drugs to their health care appointments for review.

Unclear prescriptions

Prescriptions must be written as clearly as possible. The names of some drugs are similar and, if not written clearly, cause confusion. Changing some traditional but easily confused notations may also help reduce errors. For example, “qd” (once a day) may be confused with “qid” (4 times a day). Writing “once/day” or “once a day” is preferred. Electronically transmitted or computer-printed prescriptions can avoid problems with illegible handwriting or inappropriate abbreviations. However, electronic prescribing systems that use check boxes or pull-down lists may increase the risk of inadvertently selecting the wrong drug or dose.

Inappropriate use of drugs

Drugs may be given incorrectly, especially in institutions. A drug may be given to the wrong patient, at the wrong time, or by the wrong route. Certain drugs must be given slowly when given IV, and some drugs cannot be given simultaneously. When an error is recognized, it should be reported immediately to a clinician, and a pharmacist should be consulted. Bar codes and computerized pharmacy systems may help decrease the incidence of drug errors.

Improper storage of drugs

A pharmacist should store drugs in a manner that ensures their potency. Mail-order pharmacies should follow procedures to ensure proper transportation. Storage by patients is often suboptimal. The bathroom medicine cabinet is not an ideal storage place for drugs because of the heat and humidity. If stored incorrectly, drugs are likely to decrease in potency long before the stated expiration date.

Labeling should clearly state whether a drug needs to be stored in the refrigerator or kept cool, needs to be kept out of excessive heat or sun, or otherwise requires special storage. On the other hand, unnecessary precautions decrease adherence and waste the patient’s time. For example, unopened insulin should be refrigerated, but a bottle in use can be stored safely outside the refrigerator for a relatively long time if not exposed to excessive heat and sun.

Drug expiration date exceeded

Use of outdated drugs is common. Outdated drugs may be ineffective, and some (eg, aspirin, tetracycline) can be harmful if used when outdated.

Patient error

Drug error often results from a patient’s confusion about how to take drugs. Patients may take the wrong drug or dose. Dosing instructions for each drug, including why the drug has been prescribed, should be completely explained to patients and given in writing when possible. They should be advised to ask their pharmacist for additional advice about taking their drugs. Packaging should be convenient but safe. If children will not have access to the drug and patients may have difficulty opening the container, drugs do not need to be provided in childproof containers.

Miscommunication among health care providers

Another common source of error is inaccurate transmission of prescription information when a patient's care is transferred from one facility or provider to another (eg, from hospital to rehabilitation facility, from nursing home to hospital, or between a specialist and primary care provider). Communication between different busy providers usually requires active effort, and changes to a drug regimen are common when care is transitioned. Increased attention to communication can help decrease the risk of such errors. Risk has been decreased by various formal drug reconciliation programs, such as preparing a full list of current drugs each time a patient transfers from one facility to another.

Drugs Mentioned In This Article

Drug Name Select Trade
Anacin Adult Low Strength, Aspergum, Aspir-Low, Aspirtab , Aspir-Trin , Bayer Advanced Aspirin, Bayer Aspirin, Bayer Aspirin Extra Strength, Bayer Aspirin Plus, Bayer Aspirin Regimen, Bayer Children's Aspirin, Bayer Extra Strength, Bayer Extra Strength Plus, Bayer Genuine Aspirin, Bayer Low Dose Aspirin Regimen, Bayer Womens Aspirin , BeneHealth Aspirin, Bufferin, Bufferin Extra Strength, Bufferin Low Dose, DURLAZA, Easprin , Ecotrin, Ecotrin Low Strength, Genacote, Halfprin, MiniPrin, St. Joseph Adult Low Strength, St. Joseph Aspirin, VAZALORE, Zero Order Release Aspirin, ZORprin
Emtet-500, Panmycin, Sumycin
NOTE: This is the Professional Version. CONSUMERS: View Consumer Version
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