Objective: To evaluate the safety and efficacy of controlled-release physostigmine, an acetylcholinesterase inhibitor, in patients with probable AD of mild to moderate severity.
Methods: A prospective, 24-week, randomized, multicenter, double-blind, parallel group study of patients was conducted. The study enrolled 475 patients at 24 sites. Patients met criteria for probable AD and were randomized to one of three arms: placebo, controlled-release (CR) physostigmine 30 mg daily, or CR physostigmine 36 mg daily. Dosage was escalated by a forced upward titration during the first 6 to 9 weeks of the trial, then maintained at a constant dose to 24 weeks. Primary outcome measures were the Alzheimer's Disease Assessment Scale-Cognitive subscale (ADAS-Cog) and the Clinician's Interview-Based Impression of Change-Plus with caregiver input (CIBIC+). Secondary outcome measures included the Clinical Global Impression of Change (CGIC), the Geriatric Evaluation by Relatives Rating Instrument, and an Instrumental Activities of Daily Living Scale.
Results: In an intent-to-treat population, the last observation carried forward analysis revealed a 2.9-point ADAS-Cog (p = 0.002) difference between physostigmine and placebo-treated patients for both dosages, and a 0.26 to 0.31-point difference on the CIBIC+ (p = 0.048). There were no significant differences on the secondary outcome measures except for a difference on the CGIC when analyzed by use of the Cochran-Mantel-Haenszel statistic (p = 0.014). There were significant increases in gastrointestinal side effects including nausea, vomiting, diarrhea, anorexia, dyspepsia, and abdominal pain for patients on either dose of physostigmine, resulting in a high dropout rate. Agitation was decreased significantly. There was no evidence of cardiac rhythm disturbance or liver function abnormalities.
Conclusion: CR physostigmine enhanced cognitive and global function. It is relatively safe for the treatment of cognitive dysfunction secondary to AD. However, in light of the gastrointestinal side effects, a lower starting dose and a flexible titration schedule might lead to a more favorable adverse event profile in the clinical arena.