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: Reactions included thrombophlebitis ( 20 of 54 patients ) , rash ( 4 of 54 ) , nephrotoxicity ( 4 of 50 ) , proteinuria ( 1 of 50 ) and ototoxicity ( 1 of 11 patients tested by audiometry ) .
### Output Text:
Reactions included thrombophlebitis ( 20 of 54 patients ) , rash ( 4 of 54 ) , nephrotoxicity ( 4 of 50 ) , proteinuria ( 1 of 50 ) and ototoxicity ( 1 of 11 patients tested by audiometry ) . 