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: Oral diphenhydramine and prednisone were ineffective in preventing the recurrence of the allergic reaction .
### Output Text:
Oral <span class="chemical">diphenhydramine</span> and <span class="chemical">prednisone</span> were ineffective in preventing the recurrence of the allergic reaction . 