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: Peripheral neuropathy was observed only in 2 . 5 % of patients and deep vein thrombosis in 5 . 7 % .
### Output Text:
Peripheral neuropathy was observed only in 2 . 5 % of patients and deep vein thrombosis in 5 . 7 % . 