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: GFC produced an increased latency to first seizure , at doses 25mg / kg ( 20 . 12 + 2 . 20 min ) , 50mg / kg ( 20 . 95 + 2 . 21 min ) or 75 mg / kg ( 23 . 43 + 1 . 99 min ) when compared with seized mice .
### Output Text:
<span class="chemical">GFC</span> produced an increased latency to first seizure , at doses 25mg / kg ( 20 . 12 + 2 . 20 min ) , 50mg / kg ( 20 . 95 + 2 . 21 min ) or 75 mg / kg ( 23 . 43 + 1 . 99 min ) when compared with seized mice . 