USP Quality Review

No. 78, Issued February 2004

Too Much Similarity

Similar Tablets

Error description: A patient noticed two different medications in the prescription vial. The medications were Lipitor® 10 mg (for hypercholesterolemia) and Zyrtec® 10 mg (for allergic symptoms), both manufactured by Pfizer. The patient's prescription was for Zyrtec. A prescription for Lipitor was filled in the automatic counter first. The automatic counter may not have been fully emptied prior to filling the Zyrtec prescription. The pharmacist implicated the similar tablet color and size as a reason for not detecting the mix-up. Short staffing was also suggested as a contributing factor to this error.
Reporting pharmacist's action/recommendation: Check the automatic counter for remaining tablets after each fill and provide adequate staffing to enable double checks to be performed routinely.


Lipitor 10 mg
Zyrtec 10 mg
Photos of similar tablets†

Error description: A patient was prescribed diazepam 2 mg, but received alprazolam 2 mg (both are used to treat anxiety disorders). The bottle the patient received was labeled as diazepam 2 mg. The patient felt tired and dizzy and contacted the physician. Staffing at the pharmacy was adequate. The possible cause of this error was the similarity in the tablets' shape, color, and markings (both are manufactured by Mylan Pharmaceuticals).
Reporting pharmacist's action/recommendation: Technicians must check the NDC before counting tablets; drugs with potential for error are distinguished by red dividers; drugs with no image in the computer are placed with the original prescription.


alprazolam 2 mg
diazepam 2 mg
Photos of similar tablets†

Error description: The wrong strength, 0.112 mg vs. 0.2 mg, of Levoxyl® (manufactured by Jones Pharma, Inc.) was dispensed to the patient. The tablets are the same color, size, and shape, and the bottles are identical except for the strength.
Reporting pharmacist's action/recommendation: The two strengths are now placed in different areas of the pharmacy. The color of the bottle and tablets should be changed.


Levoxyl 0.112 mg
Levoxyl 0.2 mg
Photos of similar tablets†

Error description: Atenolol 25 mg (for hypertension), by Geneva Pharmaceuticals, and prednisone 5 mg (a corticosteroid), by West-Ward Pharmaceuticals, were packaged by a technician. The wrong prescription labels were placed on the blister cards by the technician and the stock bottles were left with the cards to be checked by the pharmacist. The error was not caught by the pharmacist, as the tablets are very similar in size, shape, and color. The nurse administering the medications to the patients caught the error.
Reporting pharmacist's action/recommendation: All drugs should be double-checked with the original stock bottles by the pharmacist. The original containers should be opened and the tablets should be examined closely (i.e., with a magnifying glass if necessary) to ensure that the appropriate product is being dispensed.


atenolol 25 mg
prednisone 5 mg
Photos of similar tablets†

†Reprinted with permission from the Drug Facts & Comparisons Drug Identifier database. © 2002