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: In general , the dihydropyridine calcium channel blockers are usually well tolerated , with headache , facial flushing , palpitations , edema , nausea , anorexia , and dizziness being the more common adverse effects .
### Output Text:
In general , the <span class="chemical">dihydropyridine</span> <span class="chemical">calcium channel blockers</span> are usually well tolerated , with headache , facial flushing , palpitations , edema , nausea , anorexia , and dizziness being the more common adverse effects . 