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 main toxic effect was myelosuppression , with Grade 3 and 4 neutropenia in 16 patients , anemia in 12 patients , thrombocytopenia in 11 patients , and neutropenic fever in 3 patients .
### Output Text:
The main toxic effect was myelosuppression , with Grade 3 and 4 neutropenia in 16 patients , anemia in 12 patients , thrombocytopenia in 11 patients , and neutropenic fever in 3 patients . 