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: After 2 weeks of treatment , patients tested 5 - 8 h after the last dose of medication did not show any decrement of performance .
### Output Text:
After 2 weeks of treatment , patients tested 5 - 8 h after the last dose of medication did not show any decrement of performance . 