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: Rhabdomyolysis and brain ischemic stroke in a heroin - dependent male under methadone maintenance therapy .
### Output Text:
Rhabdomyolysis and brain ischemic stroke in a <span class="chemical">heroin</span> - dependent male under <span class="chemical">methadone</span> maintenance therapy . 