If you are using NUCALA (mepolizumab) for patients who have eosinophilic asthma, please check to ensure the correct volume is being dispensed. In a Safety Brief in our June 28, 2018 newsletter, we mentioned that some healthcare practitioners have been confused by the vial label, which states “100 mg/vial.” However, each vial of Nucala contains approximately 144 mg of the drug (Figure 1), 
which includes overfill to facilitate dose preparation. After reading our article, one hospital decided to look back at previous dispensed doses and discovered that as many as 3 doses may have been incorrect. In these cases, the doses were prepared according to the directions on the carton, which call for the 100 mg vial to be diluted with 1.2 mL of sterile water for injection. While the carton also states that, after reconstitution, the solution concentration is 100 mg/mL, it is easy to miss this information. Furthermore, the vial label prominently states “100 mg/vial” without noting on the front of the vial label that the reconstituted strength is 100 mg/mL, or that the entire vial contains 144 mg. It appears that staff thought the vial contained only 100 mg and withdrew the entire vial contents into a syringe and dispensed it for these patients. The recommended 100 mg dose should be drawn up as 1 mL, with the overfill remaining in the vial. The vial label should prominently state “100 mg/mL” after reconstitution.
As noted in the earlier Safety Brief, the manufacturer, GlaxoSmithKline, told us that Nucala was studied during clinical trials with single doses as high as 1,500 mg intravenously, with serious adverse events occurring at a rate similar to lower dose treatment groups and without evidence of dose-related toxicities. We have asked the company to revise the container labeling to reflect the contents of each vial, and to refer users to the prescribing information for preparation and dosing instructions. Pharmacies should ensure that sterile preparation compounding instructions clearly state that only 1 mL (100 mg) should be withdrawn from the reconstituted vial.