Drug-Name Similarities and Dispensing Errors

AUGUST 01, 2005
Kate Kelly, PharmD

Confirmation Bias

One of the most common medication errors occurs when 2 drug names that look similar are confused. Human factors experts tell us that "confirmation bias" plays a role. Confirmation bias means that you are more likely to believe information that supports your view rather than information that does not. Another way of putting it is that you are more likely to see what you are most familiar with, not what is really there.

For example, a pharmacist sent a report to the Institute for Safe Medication Practices (ISMP) with a good example of confirmation bias. Several prescriptions written for "Sinequan" (doxepin) have been misread in his pharmacy as "Singulair" (montelukast). In this pharmacy, staff rarely saw prescriptions written using the brand name Sinequan. Since the drug has long been available generically, "doxepin" has been the name most often used by prescribers. On the other hand, prescriptions for "Singulair" are seen commonly. Prescribers rarely use "montelukast" when prescribing. When handwritten, the 2 drug names (Sinequan and Singulair) can look similar.

Confirmation bias led staff to see the name that was most familiar to them—Singulair—rather than what was actually being communicated—Sinequan. The fact that these drugs are both given orally, often in the same 10-mg strength at a similar dosing interval, adds to the potential for confusion. Since pharmacists preparing a medication may not be able to recognize that they have selected the wrong drug, blaming them for the error is fruitless. Instead, focus on ways of improving the system. Place reminders on containers or in your computer system to alert staff about commonly confused look-alike drug names. Improve checking accuracy by having another pharmacy staff member view completed prescriptions. During counseling, verify the purpose of the medication with the patient. Encourage prescribers to include the purpose of each medication on prescriptions.

Mix-ups Involving Zetia

ISMP received a report from a patient who had been taking Lipitor (atorvastatin) to treat hypercholesterolemia. Although her cholesterol levels were under control, her physician changed her therapy to one of the newer agents, Zetia (ezetimibe) 10 mg daily, and phoned the prescription in to the patient's pharmacy. The pharmacist transcribed the telephone order correctly, but another pharmacist misread the transcription and dispensed the antihypertensive Zestril (lisinopril) 10 mg. The patient obtained 3 refills, each time receiving the wrong medication. Meanwhile, her blood cholesterol level increased.

ISMP has also heard about a mix-up between Zetia and the beta-blocker Zebeta (bisoprolol fumarate). Zetia 10 mg was prescribed, but Zebeta 10 mg was dispensed to the patient. At the time, the pharmacist was unfamiliar with Zetia. Consequently, the physician's handwritten prescription appeared to be the more familiar drug Zebeta. Fortunately, the error was discovered after the patient took only a few doses. The patient experienced hypotension, but no permanent harm resulted. In yet another report, an order for Zetia was misinterpreted as Bextra (valdecoxib).

In each of these cases, similarities in the dose, route, and frequency contributed to the errors. In addition, several letters are the same in each drug name. When combined with poor handwriting, these similarities can lead to mix-ups. Encourage patients to check their medication bottles and read patient information leaflets before taking a medication.


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