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: The potential for tenofovir to cause a range of kidney syndromes has been established from mechanistic and randomised clinical trials .
### Output Text:
The potential for <span class="chemical">tenofovir</span> to cause a range of kidney syndromes has been established from mechanistic and randomised clinical trials . 