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: Symptoms relief in the group receiving the highest concentration of azelastine ( 2 . 0 mg twice daily ) was statistically greater than in the placebo group during all weeks of the study .
### Output Text:
Symptoms relief in the group receiving the highest concentration of <span class="chemical">azelastine</span> ( 2 . 0 mg twice daily ) was statistically greater than in the placebo group during all weeks of the study . 