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: However , compression neuropathy due to fibrotic muscle affected by pentazocine - induced myopathy has not previously been reported .
### Output Text:
However , compression neuropathy due to fibrotic muscle affected by <span class="chemical">pentazocine</span> - induced myopathy has not previously been reported . 