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: This illustrates intravenous pamidronate as a valuable therapeutic tool when milk - alkali syndrome presents as hypercalcemic emergency .
### Output Text:
This illustrates intravenous <span class="chemical">pamidronate</span> as a valuable therapeutic tool when milk - alkali syndrome presents as hypercalcemic emergency . 