A recent observational study of the incidence of pneumonia in patients with previous hip fractures found that bisphosphonate use reduced pneumonia risk by about one-quarter, in comparisons with those either not receiving osteoporosis treatment or receiving treatment with non-bisphosphonate drugs. Mortality from pneumonia was similarly reduced. It was hypothesized that effects of these drugs on immune or inflammatory function might mediate this effect. We have used the adverse event database from our recent 6-year randomized controlled trial of zoledronate in 2000 women over the age of 65 years, to determine whether a similar effect is observed using this more rigorous study design. Seventy-five women had at least one episode of pneumonia (32 [3.2%] zoledronate, 43 [4.3%] placebo) and 119 women had at least one episode of either pneumonia or a lower respiratory tract infection (57 [5.7%] zoledronate, 62 [6.2%] placebo). There were 93 pneumonia events and 167 pneumonia/lower respiratory infection events. For pneumonia, the hazard ratio associated with randomization to zoledronate was 0.73 (95% confidence interval, 0.46-1.16; P = 0.18) and the rate ratio was 0.69 (0.45, 1.04; P = 0.073). For the composite endpoint of pneumonia or lower respiratory infection, the hazard ratio was 0.90 (0.61, 1.30; P = 0.58) and the rate ratio 0.74 (0.54, 0.997; P = 0.048). The proportion of people with events changed approximately linearly over time in both groups, suggesting a progressive divergence in cumulative incidence during the study. In conclusion, these findings lend support to the hypothesis that bisphosphonate use reduces the number of lower respiratory tract infections in older women, though the present study is under-powered for this endpoint and the findings are of borderline statistical significance. Further analysis of other trials of bisphosphonates is necessary to test this possibility further, and exploration of the possible underlying mechanisms is needed.
Keywords: Bisphosphonate; Infection; Osteoporosis; Pneumonia.