FDA Advising Physicians, Pharmacists to Use Caution With Tamiflu Dosing

The FDA is alerting physicians and pharmacists to the potential for dosing errors with Tamiflu (i.e., oseltamivir phosphate) for oral suspension.

According to the agency, U.S. physicians typically write prescriptions for liquid medications in milliliters or teaspoons. However, dose recommendations on the Tamiflu package insert are provided in milligrams, and the dosing dispenser provided with the drug is marked in 30-, 45- and 60-milligram increments only.

The FDA said it has received reports of dosing errors, which could lead to a patient receiving an inadequate dose or an overdose.

Prescribers should write doses in milligrams if the dosing dispenser provided with the drug is in milligrams, said the FDA health alert. In addition, pharmacists should ensure that units of measure on a prescription match those on the dosing device provided with the drug.

The agency also said physicians should not prescribe Tamiflu for oral suspension in teaspoons and instructed pharmacists to convert such prescriptions to milliliters and to provide an appropriate measuring device.

In a letter published online in the New England Journal of Medicine, (2-page PDF; About PDFs) Kara Jacobson, M.P.H., a professor in Emory University's Rollins School of Public Health, wrote that she and her husband -- a primary care physician -- "had great difficulty determining the correct dose (of Tamiflu) to administer to their child."

"Most families and caregivers would not be able to identify or perform the cumbersome calculations required to administer Tamiflu safely to children, because the instructions on the pharmacy label, on the manufacturer’s printed label, and in the accompanying consumer medication information and the prepackage dosing syringe are misaligned," wrote Jacobson and several co-authors. "Thus, there is a high chance for dosing errors, compromised treatment or toxic effects."

The authors cautioned that even more complex dosing and measurement calculations will be required under an Emergency Use Authorization that has extended the use of oseltamivir to children under the age of 1 year.

Tamiflu is one of the tools being used to combat the novel influenza A (H1N1) virus. The CDC said Sept. 25 that visits to doctors for influenza-like illnesses are increasing nationally, and 26 states are reporting widespread influenza activity.