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: Once or twice daily dosage possible with nitrendipine and nisoldipine offers a convenient administration schedule , which encourages patient compliance in long - term therapy of hypertension .
### Output Text:
Once or twice daily dosage possible with <span class="chemical">nitrendipine</span> and <span class="chemical">nisoldipine</span> offers a convenient administration schedule , which encourages patient compliance in long - term therapy of hypertension . 