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: Clinical evaluation on combined administration of oral prostacyclin analogue beraprost and phosphodiesterase inhibitor cilostazol .
### Output Text:
Clinical evaluation on combined administration of oral <span class="chemical">prostacyclin</span> analogue <span class="chemical">beraprost</span> and phosphodiesterase inhibitor <span class="chemical">cilostazol</span> . 