The US Food and Drug Administration has issued a letter to doctors highlighting confusion that has arisen over the prescription and dispensing of Eli Lilly’s antipsychotic, Zyprexa (olanzapine), and Pfizer’s allergy drug, Zyrtec (cetirizine), because of similarities in their names.

“These reports include instances where Zyprexa was incorrectly dispensed for Zyrtec and vice versa, leading to various adverse events in some instances. These errors could result in unnecessary adverse events or potential relapse in patients suffering from schizophrenia or bipolar disorder,” the regulator’s letter stated.

In a bid to avert future errors, Lilly said it was changing the lettering on the 10mg Zyprexa bottles for easier identification – all the letters in Zyprexa will be capitalized, except for the “y”, which will be in lower case. The company is also planning to launch direct mail campaigns to pharmacists and will be placing ads in journals to focus on the dispensing error potential.