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: Given the lifelong nature of hypertension , there is a need to evaluate the long - term efficacy and tolerability of higher doses of combination anti - hypertensive therapies .
### Output Text:
Given the lifelong nature of hypertension , there is a need to evaluate the long - term efficacy and tolerability of higher doses of combination anti - hypertensive therapies . 