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By measuring VPA - induced changes of blood NH3 content , it may be possible to identify patients at higher risk of obtundation when VPA is given chronically .
 Chemical: VPA; Chemical: NH3; Chemical: VPA
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Disease, Chemical 
Text: {0} 
Answer:
 Chemical: VPA; Chemical: NH3; Chemical: VPA