A randomized, controlled trial of doxycycline and rifampin for patients with Alzheimer's disease

OBJECTIVES: To assess whether doxycycline and rifampin have a therapeutic role in patients with Alzheimer's disease (AD). DESIGN: Randomized, triple-blind, controlled trial. SETTING: Three tertiary care and two community geriatric clinics in Canada. PARTICIPANTS: One hundred one patients with probable AD and mild to moderate dementia. INTERVENTION: Oral daily doses of doxycycline 200 mg and rifampin 300 mg for 3 months. MEASUREMENTS: The primary outcome was a change in Standardized Alzheimer's Disease Assessment Scale cognitive subscale (SADAScog) at 6 months. Secondary outcomes were changes in the SADAScog at 12 months and tests of dysfunctional behavior, depression, and functional status. RESULTS: There was significantly less decline in the SADAScog score at 6 months in the antibiotic group than in the placebo group, (-2.75 points, 95% confidence interval (CI)=-5.28 to -0.22, P=.034). At 12 months, the difference between groups in the SADAScog was -4.31 points (95% CI=-9.17-0.56, P=.079). The antibiotic group showed significantly less dysfunctional behavior at 3 months. There was no significant difference in adverse events between groups (P=.34). There were no differences in Chlamydia pneumoniae detection using polymerase chain reaction or antibodies (immunoglobulin (Ig)G or IgA) between groups. CONCLUSION: Therapy with doxycycline and rifampin may have a therapeutic role in patients with mild to moderate AD. The mechanism is unlikely to be due to their effect on C. pneumoniae. More research is needed to investigate these agents.