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: Thirteen psoriatic patients with hypertension during the course of cyclosporin A therapy were treated for 25 months with a calcium channel blocker , sustained - release nifedipine , to study the clinical antihypertensive effects and adverse events during treatment with both drugs .
### Output Text:
Thirteen psoriatic patients with hypertension during the course of <span class="chemical">cyclosporin A</span> therapy were treated for 25 months with a <span class="chemical">calcium</span> channel blocker , sustained - release <span class="chemical">nifedipine</span> , to study the clinical antihypertensive effects and adverse events during treatment with both drugs . 