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 main side - effects were headache , dizziness , palpitation and flushing and these were not more frequent than reported in other studies with isradipine or with placebo .
### Output Text:
The main side - effects were headache , dizziness , palpitation and flushing and these were not more frequent than reported in other studies with <span class="chemical">isradipine</span> or with placebo . 