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: This open - labeled , multicenter study evaluated the safety of bedtime niacin extended - release / lovastatin when dosed as initial therapy and patient compliance to treatment in various clinical practice settings .
### Output Text:
This open - labeled , multicenter study evaluated the safety of bedtime <span class="chemical">niacin extended - release / lovastatin</span> when dosed as initial therapy and patient compliance to treatment in various clinical practice settings . 