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: To our knowledge , this has not previously been reported as a side effect of preoperative dipyridamole therapy , although dipyridamole - induced myocardial ischemia has been demonstrated to occur in animals and humans with coronary artery disease .
### Output Text:
To our knowledge , this has not previously been reported as a side effect of preoperative <span class="chemical">dipyridamole</span> therapy , although <span class="chemical">dipyridamole</span> - induced myocardial ischemia has been demonstrated to occur in animals and humans with coronary artery disease . 