Increased Antiviral Medication Sales Before the 2005--06 Influenza Season --- New York City

Oseltamivir, zanamivir, rimantadine, and amantadine are antiviral medications approved for the treatment and/or prophylaxis of influenza A and/or B (1), although high levels of resistance among circulating strains of influenza A led CDC to issue interim recommendations in January 2005, advising that amantadine and rimantadine not be used for the treatment or prevention of influenza A during the 2005--06 influenza season (2). As part of syndromic surveillance, the New York State Department of Health (NYSDOH) monitors sales of antiviral influenza medications paid for by the Medicaid system, and the New York City Department of Health and Mental Hygiene (NYCDOHMH) monitors sales of antiviral influenza medications by a retail pharmacy chain. Syndromic data are used in combination with data provided by laboratories, health-care facilities, and health-care providers to monitor influenza activity. In October 2005, a spike in antiviral medication sales was noted. The spike did not coincide with other markers of influenza activity but did coincide with the beginning of media coverage of avian influenza A (H5N1) and the potential for an influenza pandemic. Tracking prescription medication sales can detect spikes for which no immediate indication exists. Such syndromic data might be used to guide issuance of public health recommendations regarding the limited availability of certain medications and the inadvisability of personal stockpiling.

The New York State (NYS) Medicaid program provides health-care benefits for 34% of New York City (NYC) residents. Approximately 95% of Medicaid-paid medications are reported to NYSDOH within 1 day of sale. NYSDOH compiles a daily electronic batch file of sales with summary counts by medication category and patient postal code, age group, and sex. On average, 29,664 Medicaid-paid medications are reported from NYC each day. One medication category consists of the anti-influenza medications oseltamivir, zanamivir, and rimantadine (NYSDOH opted to exclude amantadine from its influenza antiviral category because the drug is also approved for treatment of Parkinson disease).

NYCDOHMH receives a daily electronic batch file listing certain prescription medications sold the previous day by a retail pharmacy chain. The anti-influenza medication category includes prescription sales of oseltamivir, zanamivir, rimantadine, and amantadine.

Each influenza season, during October--May (i.e., surveillance week 40 through week 20), World Health Organization (WHO) and National Respiratory and Enteric Virus Surveillance System laboratories in the United States report to CDC the weekly number of respiratory specimens received for influenza testing and the percentage of specimens testing positive for influenza by culture. In NYC, four WHO laboratories report these weekly percentages.

Previous peaks in sales of anti-influenza medication coincided with peaks in the percentage of specimens testing positive for influenza during influenza seasons 2001--02, 2002--03, 2003--04, and 2004--05 (Figure). However, a spike in antiviral influenza medication sales occurred during October 23--29, 2005 (i.e., week 43), 7 weeks before the first WHO laboratory evidence of influenza virus circulation was noted during December 11--17, 2005 (i.e., week 50). A smaller spike occurred during a similar period in 2004 (i.e., October 24--30; week 43), 1 week before any virologic evidence of circulating influenza virus. During October 2005, no other markers of influenza activity (i.e., nursing and congregate facility outbreaks, sentinel physician reporting, emergency department visits, and pneumonia and influenza mortality) indicated activity in NYC that would have signaled the start of the 2005--06 influenza season.

Reported by: J Miller, MD, K Schmit, MPH, P Duncan, C Waters, G Johnson, H Chang, PhD, B Wallace, MD, M Kacica, MD, P Smith, MD, New York State Dept of Health; D Das, MPH, S Harper, MD, R Heffernan, MPH, D Olson, MPH, B Nivin, MPH, D Weiss, MD, New York City Dept of Health and Mental Hygiene.

Editorial Note:

Influenza vaccination remains the cornerstone for the control and treatment of influenza; however, antiviral influenza medications serve as an adjunct to vaccine (1). The increased sale of antiviral influenza medications in NYC during October 2005 did not coincide with any measures of influenza activity and therefore was unlikely to reflect the treatment or prophylaxis of persons against circulating influenza viruses. However, the period of increased sales did coincide with the beginning of media coverage (3) of avian influenza (for which no human vaccine has yet been approved, although clinical trials are ongoing) and the potential for an influenza pandemic. Increased media attention to avian influenza in Asia and the resulting public concern might have produced the unprecedented demand for antiviral influenza medications in NYC before the start of the influenza season. A similar but smaller increase in sales during October 2004 coincided with media coverage of expected shortages in the influenza vaccine supply during the 2004--05 influenza season (4).

These findings suggest that persons requested and/or their health-care providers prescribed antiviral influenza medications to create personal stockpiles for use in the event of an outbreak of avian influenza or an influenza pandemic. Oseltamivir, the drug most commonly referred to in reports concerning the treatment and prophylaxis of avian influenza, has limited availability. In response to increased demand across the United States, Roche Pharmaceuticals (Nutley, New Jersey), manufacturer of oseltamivir (sold as Tamiflu^®), restricted shipment of the drug in the United States during October 2005--January 2006 (5). Because the worldwide supply of antiviral influenza medications is limited, the U.S. Department of Health and Human Services, state and local health departments, and medical societies in the United States have discouraged health-care providers from prescribing antiviral medications for the purpose of creating personal stockpiles (6--8). NYSDOH posted a health advisory on its secure Health Alert Network discouraging private stockpiling on November 10, 2005. Most of these recommendations were issued after the October spike in NYC antiviral influenza medication sales.

Although private and personal stockpiling is discouraged, federal and state health authorities and health-care institutions are creating stockpiles of antiviral influenza medications for persons at greatest risk for complications from influenza. A potential consequence of personal stockpiling is depletion of existing supplies of antivirals so that they will not be available to those persons who most need them. In addition, widespread personal stockpiling and inappropriate use of antivirals (e.g., as a daily regimen regardless of the degree of influenza risk) might compound the risk for influenza by creating conditions for the emergence of resistant strains of influenza.

The findings in this report are subject to at least three limitations. First, the exact reasons for prescribing medications are unknown. Specific clinical information on persons for whom medications were prescribed, such as recent onset of respiratory illness or personal risk factors for potential complications from influenza, was not available. Second, the degree to which media reports influenced either personal behavior or professional practice is unknown; moreover, the respective contribution of personal requests for antivirals versus physician recommendations is unknown. Finally, although county of residence is known for Medicaid prescriptions, commercial pharmacy data do not include home residence. Some sales might have been made in NYC to persons residing outside of NYC.

Monitoring both prescription and over-the-counter drug sales has become increasingly useful in public health surveillance (9,10). As indicated by the findings in this report, such syndromic data, when combined with laboratory, provider, and health-care facility surveillance, can detect spikes in sales of prescription medications for which no immediate indication exists. These data can be used to help guide public health recommendations and policies regarding limited supplies of medication and the inadvisability of personal stockpiling.

References

1. CDC. Prevention and control of influenza: recommendations of the Advisory Committee on Immunization Practices (ACIP). MMWR 2005;54(No. RR-8):22.
2. CDC. High levels of adamantane resistance among influenza A (H3N2) viruses and interim guidelines for use of antiviral agents---United States, 2005--06 influenza season. MMWR 2006;55:44--6.
3. Harris G. U.S. not ready for deadly flu, Bush plan shows. New York Times 2005; October 8, 2005.
4. Enserink M. Crisis underscores fragility of vaccine production system. Science 2004;306:385.
5. Roche Pharmaceuticals. Roche opens full national distribution for seasonal supply of Tamiflu^®. Media release. Nutley, NJ: Roche Pharmaceuticals; January 24, 2006.
6. US Department of Health and Human Services. HHS pandemic influenza plan. Washington, DC: US Department of Health and Human Services; 2005. Available at http://www.hhs.gov/pandemicflu/plan.
7. Colorado Department of Public Health and Environment. Guidelines for healthcare providers regarding stockpiling of Tamiflu. Denver, CO: Colorado Department of Public Health and Environment; October 14, 2005. Available at http://www.cdphe.state.co.us/dc/influenza/avian/tamiflu%20han.pdf.
8. Infectious Diseases Society of America. Joint position statement of the Infectious Diseases Society of America and Society for Healthcare Epidemiology of America on antiviral stockpiling for influenza preparedness 2005. Alexandria, VA: Infectious Diseases Society of America; October 31, 2005. Available at http://www.idsociety.org/template.cfmsection=home&template=/contentmanagement/contentdisplay.cfm&contentid=14970.
9. Pavlin JA, Murdock P, Elbert E, et al. Conducting population behavioral health surveillance by using automated diagnostic and pharmacy data systems. In: Syndromic surveillance: reports from a national conference, 2003. MMWR 2004;53(Suppl):166--72.
10. Wagner MM, Robinson JM, Tsui FC, et al. National retail data monitor for public health surveillance. In: Syndromic surveillance: reports from a national conference, 2003. MMWR 2004;53(Suppl):40--2.

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Date last reviewed: 3/16/2006