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 effects of a new inhaled antimuscarinic drug , oxitropium bromide , and of a slow - release theophylline preparation upon nocturnal asthma were compared in a placebo - controlled double - blind study .
### Output Text:
The effects of a new inhaled antimuscarinic drug , <span class="chemical">oxitropium bromide</span> , and of a slow - release <span class="chemical">theophylline</span> preparation upon nocturnal asthma were compared in a placebo - controlled double - blind study . 