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: Intravenous caffeine is commonly used to improve seizure duration and quality in such patients and is generally well tolerated aside from occasional reports of relatively benign ventricular ectopy .
### Output Text:
Intravenous <span class="chemical">caffeine</span> is commonly used to improve seizure duration and quality in such patients and is generally well tolerated aside from occasional reports of relatively benign ventricular ectopy . 