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: Similarly , grade 1 or 2 myalgia / arthralgia was observed in 63 . 2 % of patients , but only 14 . 3 % experienced grade 3 or 4 .
### Output Text:
Similarly , grade 1 or 2 myalgia / arthralgia was observed in 63 . 2 % of patients , but only 14 . 3 % experienced grade 3 or 4 . 