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In all three experiments a similar drug response was observed , namely that donepezil administered alone improved task performance in a dose - dependent manner ; that PNU - 120596 administered alone was without significant effect , but that the combination of PNU - 120596 with a subthreshold dose of donepezil was effective .
 Chemical: donepezil; Chemical: PNU - 120596; Chemical: PNU - 120596; Chemical: donepezil
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 Chemical: donepezil; Chemical: PNU - 120596; Chemical: PNU - 120596; Chemical: donepezil