Practitioners' Reporting News

Labeling for PEG-Intron™ May Cause Confusion

Issued June 14, 2001

The USP Medication Errors Reporting (MER) Program received four reports concerning the labeling of PEG-Intron™ (Peg-interferon alpha-2b), a drug used in the treatment of chronic hepatitis C. The reports received by USP described potential errors; no actual errors have been reported. The practitioners reporting were concerned that the labeling on the product has the potential to cause errors in ordering and/or administering the product.

PEG-Intron is provided by its manufacturer, Schering Coporation, as a lyophilized powder in a 2-mL vial for subcutaneous use. Four concentrations are currently available. All strengths are designed to be reconstituted in 0.7mL of Sterile Water for Injection. From a reconstituted vial, 0.5mL or less is intended to be administered, and, the remaining volume is provided as overfill.

Specific concern has been expressed that those practitioners familiar with the product during clinical trials may be confused by the newly approved labeling because they may not be aware that the labeling of strength changed to mcg/mL. Before FDA approval, PEG-intron labels expressed the concentration as micrograms per 0.5mL: the vials were labeled as 50mcg/0.5mL, 100mcg/0.5mL, and 150mcg/0.5mL. Since approval in January 2001, the manufacturer has revised the labeled concentration to reflect micrograms per one milliliter, even though the vials are still designed to be reconstituted in only 0.7mL of Sterile Water for Injection and only 0.5mL or less is intended to be administered. The vials are now labeled as 100mcg/mL, 160mcg/mL, 240mcg/mL, and 300mcg/mL respectively. Note that a fourth strength had been added.

Although the concentration on the revised labeling is accurate, it may mislead practitioners to think that the vials actually contain the 1mL volume indicated on the label. It requires careful inspection to realize that the total volume contained in each vial is not 1mL. One pharmacist is concerned that the labeling may result in misunderstanding and confusion in the dispensing and selection of the appropriate vial size.

According to the package insert, the manufacturer recommends selecting a 100-mcg/mL vial for doses of 40 or 50mcg, a 160-mcg/mL vial for doses of 64 or 80mcg, a 240-mcg/mL vial for doses of 96 or 120mcg, and a 300-mcg/mL vial for a 150mcg dose (see Table 1).

Table 1. Recommended Dosing
Vial Strength to Use (mcg/mL)	Weight (kg)	Amount of PEG-Intron to Administer (mcg)	Volume of PEG-Intron to Administer (mL)
100	37-45 46-56	40 50	0.4 0.5
160	57-72 73-88	64 80	0.4 0.5
240	89-106 107-136	96 120	0.4 0.5
300	137-160	150	0.5

To help reduce errors related to the dispensing and administration of PEG-Intron, all staff need to be informed regarding the manner in which the product is intended to be prepared, dispensed, and administered, as provided in the manufacturer's package insert.

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.