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: Doses in more than 90 % of randomized patients in the high - and low - dose groups were titrated to their assigned target , and the mean doses of blinded medication in both groups remained similar throughout the study .
### Output Text:
Doses in more than 90 % of randomized patients in the high - and low - dose groups were titrated to their assigned target , and the mean doses of blinded medication in both groups remained similar throughout the study . 