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: A 27 - year - old male patient presented with a maculopapular eruption on the flexural areas and buttocks after using oral ketoconazole .
### Output Text:
A 27 - year - old male patient presented with a maculopapular eruption on the flexural areas and buttocks after using oral <span class="chemical">ketoconazole</span> . 