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: By inhibiting the cytochrome P450 2D6 , terbinafine had decreased metoprolol ' s clearance , leading in metoprolol accumulation which has resulted in clinically significant sinus bradycardia .
### Output Text:
By inhibiting the cytochrome P450 2D6 , <span class="chemical">terbinafine</span> had decreased <span class="chemical">metoprolol</span> ' s clearance , leading in <span class="chemical">metoprolol</span> accumulation which has resulted in clinically significant sinus bradycardia . 