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: Pentamidine - induced torsade de pointes may be related to serum magnesium levels and hypomagnesemia may synergistically induce torsade .
### Output Text:
<span class="chemical">Pentamidine</span> - induced torsade de pointes may be related to serum <span class="chemical">magnesium</span> levels and hypomagnesemia may synergistically induce torsade . 