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: Renal Fanconi syndrome and myopathy after liver transplantation : drug - related mitochondrial cytopathy ?
### Output Text:
Renal Fanconi syndrome and myopathy after liver transplantation : drug - related mitochondrial cytopathy ? 