WASHINGTON, DC (Reuters Health) - Although the patient's family may not notice, individuals with Alzheimer's disease maintain a sustained response to anti-dementia medications, investigators reported here this week.

The initial effects of the anti-dementia drugs on symptoms of Alzheimer's disease wane over time, but remain beneficial by slowing disease progression, Dr. Susan D. Rountree, of Baylor University in Houston, reported at the 132nd annual meeting of the American Neurological Association.

Guidelines addressing duration of therapy have not been established for donepezil, galantamine, rivastigmine and memantine, Rountree said. She and her colleagues evaluated cumulative drug exposure, calculated as years of drug use and disease duration, in 643 patients with probable Alzheimer's disease.

The investigators conducted neuropsychiatric testing when the study began and annually for an average of more than 3 years up to 10 years.

"There was a persistently slower rate of decline on all the cognitive measures and basic activities of daily living," Rountree told Reuters Health. Treatment did not affect the rate of decline on the more complex tasks, but the magnitude of the initial reduction in dementia with treatment initiation was retained over time, she added.

"Benefits were seen even in those with advanced disease," Rountree said. The findings suggest that patients who use anti-dementia drugs persistently derive more benefits from therapy than those who use these drugs less persistently.

These results should be of value to the families of Alzheimer's disease patients, who become discouraged with what they perceive to be a wearing-off of the effectiveness of these drugs, she commented.