Is Oseltamivir (Tamiflu®) Safe? Re-examining the Tamiflu 'Ado' from Japan

Etsuji Okamoto


Expert Rev Pharmacoeconomics Outcomes Res. 2010;10(1):17-24. 

In This Article

Surveys/Studies in the USA & UK

In response to numerous adverse drug-related events (ADR) reported from Japan, researchers conducted retrospective cohort studies using existing data in the USA and UK.

Studies on Health Insurance Claims in the USA

For the US population, health insurance claims data of three recognized databases, namely UnitedHealthCare Ingenix Research Data Mart (RDM; 1 November 1999–30 April 2005, covering 20 million individuals),[6] Thomson Healthcare MarketScan Commercial Claims and Encounters Database and Medicare Supplemental and Coordination of Benefits Database (MedStat, 2000–2006 seasons, covering 25 million individuals of all ages), were analyzed.[7] The outcome measures of both studies had wide time frames between the index date and NPAEs: both studies recorded measures at 14 and 30 days. Since the incidence of NPAEs may increase shortly after the ingestion of oseltamivir, as Hama pointed out, one should be cautioned against the possibility that nonspecific events during the long time frame might have concealed the difference. By contrast, the same retrospective study using Japan's health insurance claims by Okamoto limited the time window to 3 days, which will be discussed later.

Both databases were analyzed with propensity score matching and results were in favor of oseltamivir: RDM and MedStat demonstrated that oseltamivir-treated patients had a significantly lower risk of NPAEs than those otherwise (odds ratio [OR]: 0.89; 95% CI: 0.85–0.94 and OR: 0.76; 95% CI: 0.68–0.84, respectively). The tendency remained consistent with logistic regression: RDM (OR: 0.65; 95% CI: 0.58–0.72) and MedStat (OR: 0.74; 95% CI: 0.61–0.90).

Another retrospective cohort study was conducted using TRICARE (health insurance system for dependent family members of the US military personnel) database on the pediatric beneficiaries aged 1 through to 21 years who received diagnoses of influenza from 1 October 2006 to 30 September 2007.[8] Cross-tabulations and propensity-adjusted logistic regression analyses were performed to compare the frequency of NPAEs among those treated with oseltamivir with those otherwise. The prevalence of NPAEs was 3.0 and 3.8%, respectively (p < 0.05). A statistically significant protective effect of oseltamivir treatment was suggested in a propensity-adjusted regression model (prevalence OR: 0.82; 95% CI: 0.69–0.96). The authors concluded that their retrospective study had found no evidence that oseltamivir had increased the risk of NPAEs among the study population.

Study using the Practice Database in the UK

A study among general practitioners in the UK using the General Practice Research Database (GPRD) identified 68,771 influenza patients diagnosed between 1 October and 31 March 2001, who were found to be at a 75% increased risk for NPAEs compared with the general population (RR: 1.75; 95% CI: 1.54–1.98). However, the frequency of using oseltamivir was much less than Japan: only 56 patients (seven of those aged ≤ 16 years) received oseltamivir, none of whom experienced a NPAE.[4]


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