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: Nine weeks after pre - treatment , dogs were given four courses of either doxorubicin ( 1 . 5 mg / kg ) or SM - 5887 ( 2 . 5 mg / kg ) once every 3 weeks .
### Output Text:
Nine weeks after pre - treatment , dogs were given four courses of either <span class="chemical">doxorubicin</span> ( 1 . 5 mg / kg ) or <span class="chemical">SM - 5887</span> ( 2 . 5 mg / kg ) once every 3 weeks . 