Confusing Zerbaxa Label Could Lead to Dosing Errors: FDA

Megan Brooks


May 20, 2015

There is a risk for dosing errors with the dual antibacterial ceftolozane/tazobactam (Zerbaxa, Cubist Pharmaceuticals) due to confusion about the drug strength displayed on the vial and carton labeling, the US Food and Drug Administration (FDA) warned healthcare providers in a safety communication today.

The FDA approved Zerbaxafor treatment of complicated intra-abdominal infections (in combination with metronidazole) and complicated urinary tract infections in adults in December 2014.

Zerbaxa's vial label was initially approved with a strength that reflects each individual active ingredient (eg, 1 g/0.5 g); however, the product is dosed based on the sum of these ingredients (eg, 1.5 g), the FDA explains in their safety communication.

"To prevent future medication errors, the strength on the drug labeling has been revised to reflect the sum of the two active ingredients. Thus, one vial of Zerbaxa will now list the strength as 1.5 grams equivalent to ceftolozane 1 gram and tazobactam 0.5 gram," the agency says.

The FDA has photos of the old and new label on its website, along with the full safety communication.

Since approval of Zerbaxa, the FDA has investigated seven reported cases of medication errors with the dual antibacterial that occurred during preparation of the dose in the pharmacy due to confusion with the display of the strength of individual ingredients on Zerbaxa's vial label and carton labeling.

In four cases, an incorrect dose was given to the patient, but no adverse events were reported. In the other three cases, the pharmacists identified the error before the drug was administered to patients, according to the FDA.

"Listing the individual drug strengths led to confusion because it was different from labeling for other beta-lactam/beta-lactamase antibacterial drugs that express strength as the sum of the 2 active ingredients. In some cases, this led to administration of 50% more drug than was prescribed," the FDA notes. No adverse events were reported among these seven cases.

The FDA encourages healthcare professionals and patients to report side effects and medication errors involving Zerbaxa to the FDA MedWatch program, the FDA's safety information and adverse event reporting program, by telephone at 1-800-FDA-1088; by fax at 1-800-FDA-0178; online at; with postage-paid FDA form 3500, available at; or by mail to MedWatch, 5600 Fishers Lane, Rockville, Maryland 20852-9787.


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