Oseltamivir Oral Suspension Concentration Revised to Ensure Accurate Dosing

Manufacturer Launches Take-back Program for Old Product

July 20, 2011 04:00 pm News Staff

Physicians should be aware of important safety changes being made to the antiviral medication oseltamivir phosphate for oral suspension, which is marketed as Tamiflu, to reduce the possibility of medication errors.

The FDA said in a July 11 safety announcement(www.fda.gov) that the concentration of the neuraminidase inhibitor is changing from 12 mg/mL to 6 mg/mL. The agency said the lower concentration is less likely to become frothy when shaken, ensuring an accurate measurement.

FDA Approves 2011-12 Flu Vaccine; Shipments Under Way

The FDA announced(www.fda.gov) July 18 that it had approved the formulation that will be used by the six manufacturers licensed to produce and distribute seasonal influenza vaccine for the United States in 2011-12.

The trivalent vaccine protects against the virus strains that -- based on global surveillance -- are expected to be the most common during the flu season. The three 2011-12 strains are the same as those used during the 2010-11 flu season:

  • A/California/7/09 (H1N1)-like virus (pandemic 2009 influenza virus)
  • A/Perth /16/2009 (H3N2)-like virus
  • B/Brisbane/60/2008-like virus

At least four of the six manufacturers had announced that they have started shipping flu vaccine as of July 19.

Manufacturer Genentech said in a letter to pharmacists that it has initiated a take-back program for the 12 mg/mL version of the product, which will no longer be marketed after current supplies are depleted. Distribution of the 6 mg/mL concentration of oseltamivir is expected to begin by the end of July, the FDA said. Genentech's take-back program is intended to reduce overlap between the two products.

The FDA issued a public health alert in 2009 after it received reports of dosing errors with the drug. The agency said at the time that U.S. physicians typically write prescriptions for liquid medications in milliliters or teaspoons, but the dosage recommendations on the package insert of 12 mg/mL oseltamivir were provided in milligrams.

Genentech has addressed that issue(www.gene.com) by packaging the 6 mg/mL version of oseltamivir with a new measuring device that uses milliliters and updating the dosing table that accompanies the product with a column for milliliters. The product's container labels and carton packaging will be updated to reflect the changes.

Based on those changes, the FDA issued the following information for physicians:

  • Prescribers should include the new (6 mg/mL) concentration and dose in milliliters on prescriptions for oseltamivir for oral suspension. An updated dosing chart is included in the revised product label.
  • It's possible that patients may receive either concentration at pharmacies during the 2011-12 flu season, and patients should be educated about this possibility to avoid medication errors.
  • The two versions of the product label may be in circulation during the 2011-12 influenza season and contain different dosing and compounding instructions for the oral suspension.
  • Prescribers should be aware that pediatric strength oseltamivir capsules -- 30 mg and 45 mg -- remain available and have not changed. These capsules can be prescribed for pediatric patients who can swallow capsules. For patients who cannot swallow capsules, these can be opened and the capsule contents can be mixed with flavored foods.
  • Report adverse events or medication errors involving oseltamivir to the FDA's MedWatch program(www.accessdata.fda.gov).