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Recently , the concern of using ketamine in these patients has been challenged by a number of published studies demonstrating that the use of ketamine was safe in these patients .
 Chemical: ketamine; Chemical: ketamine
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: ketamine; Chemical: ketamine