FDA issues corrections on dosage of Tamiflu

By Sheilah Downey

Conflicting directions that accompany prescriptions to Tamiflu could lead to "serious potential for dosing errors," and prompted a public safety alert from the Food and Drug Administration.

When their daughter was diagnosed with the H1N1 virus, a doctor and his wife, also a medical professional, had to determine the correct dosage of  Tamiflu by using this equation: 5ml (volume of teaspoon) x 0.75 x 12mg/mill = 45mg on the syringe.

The problem, says doctors, is the Tamiflu comes with syringe markings in milligrams while the prescription specifies the dose in teaspoons. Kara Jacobson, an MPH, and her doctor-husband, had to perform the math to dose their daughter. It took them 30 minutes.

"Most families and caregivers would not be able to identify or perform the cumbersome calculation," wrote Jacobson and colleagues in the New England Journal of Medicine online first edition.

Jacobson warned of possible "dosing errors, compromised treatment, or toxic effects."

The FDA, perhaps acutely aware that most people can't balance their checkbooks, issued a public health notice (which follows) about the discrepancy this week.

"Prescribers and pharmacists should be alert for potential dosing errors with Tamiflu (oseltamivir) for Oral Suspension. U.S. health care providers usually write prescriptions for liquid medicines in milliliters (mL) or teaspoons, while Tamiflu is dosed in milligrams (mg). The dosing dispenser packaged with Tamiflu has markings only in 30, 45 and 60 mg. The Agency has received reports of errors where dosing instructions for the patient do not match the dosing dispenser. Health care providers should write doses in mg if the dosing dispenser with the drug is in mg.

Pharmacists should ensure that the units of measure on the prescription instructions match the dosing device provided with the drug."