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: Few days later , the patient used another 200 mg ketoconazole tablet , and within an hour experienced a similar clinical picture , which resolved again spontaneously within hours .
### Output Text:
Few days later , the patient used another 200 mg <span class="chemical">ketoconazole</span> tablet , and within an hour experienced a similar clinical picture , which resolved again spontaneously within hours . 