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 PMs , metoprolol increased the terbutaline area under the plasma concentration vs . time curve ( + 67 % ) .
### Output Text:
In PMs , <span class="chemical">metoprolol</span> increased the <span class="chemical">terbutaline</span> area under the plasma concentration vs . time curve ( + 67 % ) . 