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: Severe complications of antianginal drug therapy in a patient identified as a poor metabolizer of metoprolol , propafenone , diltiazem , and sparteine .
### Output Text:
Severe complications of antianginal drug therapy in a patient identified as a poor metabolizer of <span class="chemical">metoprolol</span> , <span class="chemical">propafenone</span> , <span class="chemical">diltiazem</span> , and <span class="chemical">sparteine</span> . 