In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: However , DCF continued to be effective in reducing pelvic pain for two hours , whereas GTN scores remained more or less stable after 30 min and significantly higher than those for DFC ( after one hour : GTN , - 12 . 8 + / - 17 . 9 ; DFC , - 18 . 9 + / - 16 . 6 and after two hours : GTN , - 23 . 7 + / - 20 . 5 ; DFC , - 59 . 7 + / - 17 . 9 , p = 0 . 0001 ) .
### Output Text:
However , <span class="chemical">DCF</span> continued to be effective in reducing pelvic pain for two hours , whereas <span class="chemical">GTN</span> scores remained more or less stable after 30 min and significantly higher than those for DFC ( after one hour : <span class="chemical">GTN</span> , - 12 . 8 + / - 17 . 9 ; DFC , - 18 . 9 + / - 16 . 6 and after two hours : <span class="chemical">GTN</span> , - 23 . 7 + / - 20 . 5 ; DFC , - 59 . 7 + / - 17 . 9 , p = 0 . 0001 ) . 