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: In those with symptoms of hearing loss , the drug should be stopped for four weeks , and when the audiogram is stable or improved , therapy should be restarted at 10 to 25 mg / kg per dose .
### Output Text:
In those with symptoms of hearing loss , the drug should be stopped for four weeks , and when the audiogram is stable or improved , therapy should be restarted at 10 to 25 mg / kg per dose . 