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: Drug - induced long QT syndrome in injection drug users receiving methadone : high frequency in hospitalized patients and risk factors .
### Output Text:
Drug - induced long QT syndrome in injection drug users receiving <span class="chemical">methadone</span> : high frequency in hospitalized patients and risk factors . 