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: Acute bronchodilating effects of ipratropium bromide and theophylline in chronic obstructive pulmonary disease .
### Output Text:
Acute bronchodilating effects of <span class="chemical">ipratropium bromide</span> and <span class="chemical">theophylline</span> in chronic obstructive pulmonary disease . 