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 few minutes after administration of the drugs , they presented urticaria ( patients 1 and 2 ) and conjunctivitis ( patient 1 ) .
### Output Text:
A few minutes after administration of the drugs , they presented urticaria ( patients 1 and 2 ) and conjunctivitis ( patient 1 ) . 