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: RESULTS : Both valsartan and amlodipine were effective at lowering blood pressure at 4 , 8 , and 12 weeks .
### Output Text:
RESULTS : Both <span class="chemical">valsartan</span> and <span class="chemical">amlodipine</span> were effective at lowering blood pressure at 4 , 8 , and 12 weeks . 