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: The patient described developed chronic active hepatitis after six months therapy with diclofenac sodium which progressed despite the withdrawal of the drug , a finding not previously reported .
### Output Text:
The patient described developed chronic active hepatitis after six months therapy with <span class="chemical">diclofenac sodium</span> which progressed despite the withdrawal of the drug , a finding not previously reported . 