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: A seventy - eight - year - old woman presented with complete heart block and refractory hypotension two days after a therapeutic dose of sustained - release verapamil with concomitant use of metoprolol .
### Output Text:
A seventy - eight - year - old woman presented with complete heart block and refractory hypotension two days after a therapeutic dose of sustained - release <span class="chemical">verapamil</span> with concomitant use of <span class="chemical">metoprolol</span> . 