Practitioners' Reporting News

Zyrtec and Zyprexa Confusion

Issued May 23, 2005

USP continues to receive reports on the mix-ups associated with Zyrtec® (cetirizine) by Pfizer and Zyprexa® (olanzapine) by Lilly. The FDA-approved indications for each of these drugs differ considerably. Zyprexa is indicated for the short-term and maintenance treatment of schizophrenia and is also indicated for the short-term treatment of acute mixed or manic episodes associated with bipolar I disorder and as a maintenance treatment in bipolar disorder (normal dose 5 to 10 mg/day), while Zyrtec is indicated for the treatment of allergic rhinitis or chronic urticaria (normal dose 5 to 10 mg/day). Many similarities exist in these two products, including names starting with the same two letters, the availability of the same strengths, the same dosing intervals and the fact that these two products are generally stored next to or near each other on pharmacy shelves. The following are case examples:

A prescription for a refill of Zyrtec 10 mg was picked up at the pharmacy by a patient's husband. The prescription was labeled correctly but was misfilled with Zyprexa 10 mg. The patient took one dose of Zyprexa and experienced drowsiness, fatigue, migraine, staggering and stuttering, dry mouth, muscle twitching, and actually fainted at work. The patient called the pharmacist to confirm the prescription only to find out that the medication was incorrectly filled at the pharmacy. The patient was seen by a physician the next day.

A pharmacist misinterpreted a prescription for the antihistamine Zyrtec and filled the prescription with Zyprexa 10 mg which was taken by the patient. The patient experienced elevated blood pressure, headache, somnolence, dizziness, nausea and vomiting. The patient's allergies were not addressed, so the patient had endless sneezing, red and swollen eyes, and felt so bad that 2 days of work were missed. The patient notified the pharmacy and the primary care physician.

A community pharmacist refilled a prescription for Zyprexa 10 mg with Zyrtec 10 mg. These products are stored side by side on the pharmacy shelf. Patient counseling was provided when the original prescription was dispensed but not on this refill. An alert patient realized that the wrong medication had been dispensed and returned it to the pharmacy. The pharmacy has taken action to prevent future errors by separating these products on the pharmacy shelf.

A physician ordered Zyrtec 10 mg at bedtime for a patient with congestion. The pharmacist entered the order into the hospital computer system as Zyprexa 10 mg at bedtime. The patient received six incorrect doses. After the first dose, the patient fell and hit her head which required x-rays and a CT scan. The patient complained of pain and soreness for four days after the fall. The medication error was discovered while the physician was reviewing the patient's chart because the patient was still complaining of congestion.

A geriatric patient with pneumonia, coronary artery disease and hypertension was mistakenly given Zyprexa 10 mg instead of Zyrtec 10 mg, which resulted in a decreased level of consciousness in this patient. Fortunately, the patient experienced no lasting harm from this mix-up.

On January 26, 2005, Eli Lilly and Company issued a "Dear Healthcare Professional" letter to alert practitioners about the medication dispensing and prescribing errors that have been reported. According to the company these errors could result in unnecessary adverse events or potential relapse in patients suffering from schizophrenia or bipolar disorder.

The measures that Lilly has taken or will be taking to help reduce the potential for future errors are:

  • Changes to the appearance of the drug name as printed on the label of 10 mg bottles from Zyprexa to ZyPREXA, for easier identification http://zyprexa.com/pdf/zyp_packaging.pdf
  • Launch an awareness direct mail campaign to pharmacists
  • Sponsor medication error prevention continuing education
  • Purchase space for journal ads focusing on this dispensing error potential, with emphasis on good prescribing and good dispensing practices.

Practitioner's can learn from your experiences. If you have similar cases to share, report them to MER at www.usp.org/patientSafety/mer/. Reporting forms can also be printed at that address, or requested by calling 1-800-23-ERROR (1-800-233-7767).


Readers are advised that official USP cautions and warnings for drugs appear in the USP–NF or USP DI. Unless otherwise indicated, any advice or opinions expressed herein reflect solely the judgment of USP staff. Such statements are intended for further consideration and evaluation and may or may not be applicable to a particular practice. The USP Medication Errors Reporting Program is presented in cooperation with the Institute for Safe Medication Practices.