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Animal and clinical studies have suggested that N - methyl - D - aspartate ( NMDA ) antagonists , such as ketamine , may be effective in improving opioid analgesia in difficult pain syndromes , such as neuropathic pain .
 Chemical: N - methyl - D - aspartate; Chemical: NMDA; Chemical: ketamine; Disease: pain; Disease: neuropathic pain
Given options, please tell me the categories of all the listed entity words.Output format is "type1: word1; type2: word2". 
Option: Disease, Chemical 
Text: {0} 
 Entities: N - methyl - D - aspartate, NMDA, ketamine, pain, neuropathic pain 
Answer:
 Chemical: N - methyl - D - aspartate; Chemical: NMDA; Chemical: ketamine; Disease: pain; Disease: neuropathic pain