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: No significant difference was noticed between results obtained with either active drug , as well as with either dosage of oxitropium .
### Output Text:
No significant difference was noticed between results obtained with either active drug , as well as with either dosage of <span class="chemical">oxitropium</span> . 