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: The loading dose was 800 mg / day for 6 weeks and the maintenance dose was 600 mg / day .
### Output Text:
The loading dose was 800 mg / day for 6 weeks and the maintenance dose was 600 mg / day . 