19179
Patients aged > 70 years who received at least two prescriptions for donepezil , rivastigmine , galantamine and memantine between January 2006 and December 2010 were included in the study .
 donepezil, rivastigmine, galantamine, memantine
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 donepezil, rivastigmine, galantamine, memantine