21836
Antinociceptive effects of BTX - A in formalin and sciatic nerve transection - induced pain were prevented by non - selective opioid antagonist naltrexone .
 Chemical: formalin; Chemical: naltrexone
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: formalin; Chemical: naltrexone