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: Significant increases in drowsiness were reported in patients treated with ketamine in both groups and were more marked with ketamine 0 . 50 mg / kg .
### Output Text:
Significant increases in drowsiness were reported in patients treated with <span class="chemical">ketamine</span> in both groups and were more marked with <span class="chemical">ketamine</span> 0 . 50 mg / kg . 