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: Reversible inferior colliculus lesion in metronidazole - induced encephalopathy : magnetic resonance findings on diffusion - weighted and fluid attenuated inversion recovery imaging .
### Output Text:
Reversible inferior colliculus lesion in <span class="chemical">metronidazole</span> - induced encephalopathy : magnetic resonance findings on diffusion - weighted and fluid attenuated inversion recovery imaging . 