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: The adverse events during combined therapy with cyclosporin A and nifedipine included an increase in blood urea nitrogen levels in 9 of the 13 patients and development of gingival hyperplasia in 2 of the 13 patients .
### Output Text:
The adverse events during combined therapy with <span class="chemical">cyclosporin A</span> and <span class="chemical">nifedipine</span> included an increase in <span class="chemical">blood urea nitrogen</span> levels in 9 of the 13 patients and development of gingival hyperplasia in 2 of the 13 patients . 