Survival Analysis

One final technique, recently developed to enhance the information content of spontaneous case reports data, employs principles of time-to-event and survival analysis to the evaluation of ADR reports (Kahn and Sempos, 1989; Graham and Green, 1999). The technique requires access to nationally representative population-based drug use data in order to model the pattern of duration of use in the general population. In a clinical trial or longitudinal observational cohort study, patients who drop out before study completion are censored at that point in time and only the time during which they were in the study is considered in the analysis (Meinert, 1986). Life-table techniques are a common means of accurately accounting for changes in the size of the population at risk resulting from withdrawals (Clayton and Hills, 1993; Kelsey et al., 1996). By use of this method, one can calculate interval-specific reporting/hazard rates (e.g. for the first month, fifth month or twelfth month of product use) as well as the cumulative risk of an ADR being reported through a given point in time such as after one or three years of continuing drug use.

The method is complex but useful. It was used to demonstrate the association between risk of developing acute liver failure and the duration of use of trovafloxacin, a fluoroquinolone antibiotic. Over about a two-year period, the FDA received 14 reports of acute liver failure associated with

Table 17.3. Life-table estimation of reporting rates of acute liver failure with trovafloxacin.




Days of follow-up

Interval hazard rate (per 106 person-years)

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