Analysis of adverse effects during amantadine prophylaxis in a nursing home population

Objective: To evaluate adverse reactions during amantadine prophylaxis in a nursing home population, and to identify baseline characteristics that were associated with their development. Design: A retrospective chart review. Setting: A 233-bed teaching nursing home. Main Results: Amantadine prophylaxis was given to 199 of 210 residents (95 percent), 19 of whom died during the one-month period of amantadine prophylaxis. None of the deaths were attributed to amantadine. Of the surviving residents, 26 percent developed adverse effects after an average of two weeks of amantadine prophylaxis. The majority of adverse effects involved the central nervous system, including change in mental status in 40 percent, agitation or disruptive behavior in 34 percent, hallucinations in 19 percent, and mood changes in 19 percent. All adverse effects resolved. Baseline characteristics regarding age, gender, serum creatinine, number of medications, and dosage of amantadine of the residents who experienced adverse effects were similar to those of patients who did not. Adverse effects tended to occur less often in patients with an underlying cardiovascular illness than in those without (odds ratio = 0.52; confidence interval = 0.27-1.0). There was no obvious explanation for this association, which approached statistical significance. Patients with an underlying psychiatric disorder tended to develop adverse effects almost twice as often as those without, but this trend was also not statistically significant (odds ratio = 1.9; confidence interval = 0.93-3.8). Conclusions: Amantadine prophylaxis was associated with reversible adverse effects in 26 percent of these nursing home residents. Earlier identification of adverse effects (and subsequent dose reduction) with a prospective surveillance checklist might have lessened the severity and duration of adverse effects.