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 decrease in reticulocyte count was dose related between 600 and 900 mg / day with no further change when the dose was escalated to 1200 mg / day .
### Output Text:
The decrease in reticulocyte count was dose related between 600 and 900 mg / day with no further change when the dose was escalated to 1200 mg / day . 