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: OBJECTIVE : This is to present reversible inferior colliculus lesions in metronidazole - induced encephalopathy , to focus on the diffusion - weighted imaging ( DWI ) and fluid attenuated inversion recovery ( FLAIR ) imaging .
### Output Text:
OBJECTIVE : This is to present reversible inferior colliculus lesions in <span class="chemical">metronidazole</span> - induced encephalopathy , to focus on the diffusion - weighted imaging ( DWI ) and fluid attenuated inversion recovery ( FLAIR ) imaging . 