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: Dose reductions were needed in 31 % of patients and permanent discontinuation in 38 . 9 % .
### Output Text:
Dose reductions were needed in 31 % of patients and permanent discontinuation in 38 . 9 % . 