Older flu drugs still used, against CDC advice

Influenza, General

Jan 24, 2008 (CIDRAP News) – A recent survey suggests that about a quarter of primary care physicians (PCPs) were still prescribing older antiviral drugs for influenza during the last flu season, despite a federal warning to avoid them because of viral resistance, according to the Centers for Disease Control and Prevention (CDC).

In the survey of 730 physicians in four states, 26.4% reported prescribing amantadine or rimantadine to some patients in the 2006-07 flu season, according to the report in the CDC's Morbidity and Mortality Weekly Report. In January 2006 the CDC recommended that physicians stop using the two drugs because of high rates of resistance in circulating strains of influenza A.

The survey also showed that 69% of physicians ordered influenza tests for patients with influenza-like illness (ILI), and most of those ordered rapid antigen tests. Because rapid tests miss up to 30% of flu cases, the CDC says, physicians should exercise clinical judgment when using them.

Survey specifics
The survey covered 4 of the 10 sites in the CDC's Emerging Infections Program, a network of state health departments, academic institutions, and local collaborators working to assess the effects of emerging infections and methods for combating them. The four sites were New Haven County in Connecticut, seven counties in the Minneapolis–St. Paul area, four urban counties in New Mexico, and 15 counties in the Albany and Rochester, N.Y., areas.

Surveys were mailed to random samples of PCPs in the four areas in March and April of 2007 and were sent two more times to nonrespondents. Physicians were asked whether they had evaluated patients with ILI, whether they had used influenza tests and what types, and whether they had prescribed antiviral drugs and what types. Those who had not examined patients with ILI were excluded.

About 47% of the physicians responded to the survey, and 730 of those (58%) met the inclusion criteria. Of the 730, 36.7% were in family practice, 29.2% in internal medicine, 27.9% in pediatrics, and 6.2% in obstetrics/gynecology.

Antiviral prescriptions
About 54% of the physicians reported prescribing antiviral drugs to at least some patients, with the rates ranging from 41.7% for pediatricians to 66.4% for family practice.

The most commonly prescribed antiviral by far was oseltamivir (Tamiflu), a neuraminidase inhibitor, used by 87% of the respondents. The two older drugs, amantadine and rimantadine, were prescribed by 17.8% and 8.7%, respectively. Zanamivir (Relenza), the other licensed neuraminidase inhibitor, was prescribed by 5.3% of the physicians.

Amantadine use was highest in New Mexico (43.2% of doctors), followed by Minnesota (16.6%) and New York (14.2%), the report says. Respondents in Connecticut reported the highest use of oseltamivir (94.7%), followed by those in Minnesota (90.2%), New York (85.8%), and New Mexico (70.3%).

In light of the findings on antiviral prescribing, the CDC article calls for more education efforts to make PCPs aware of current treatment recommendations. The report also says that pediatric patients treated with oseltamivir should be watched closely for signs of neuropsychiatric effects, such as hallucinations, delirium, or abnormal behavior. Such effects have been reported in a number of young patients in recent years, mostly in Japan.

Influenza testing
A large majority—69%—of the responding doctors reported using a flu test during the flu season. The use of testing ranged from 87.1% of the Minnesota doctors to 55.0% of those in New Mexico. Of those who ordered tests, 88.0% used rapid antigen testing, 18.8% ordered viral culture, and 6.3% ordered serologic tests.

The CDC says many rapid antigen tests for flu can be handled by nonlaboratorians in office settings, which may explain why many physicians choose them. "However, the benefit of obtaining results quickly must be weighed against the low sensitivities of the tests (70%-75%)," the report says. Consequently, "PCPs should use clinical judgment and check reports of weekly influenza activity from CDC and their individual state health departments to guide their clinical decisions."

CDC. Influenza-testing and antiviral-agent prescribing practices—Connecticut, Minnesota, New Mexico, and New York, 2006-07 influenza season. MMWR 2008 Jan 25;57(3):61-5 [Full text]

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