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: Concern has been raised with regard to the safety of lorazepam in this age group , especially in very - low - birth - weight ( VLBW ; < 1 , 500 g ) infants .
### Output Text:
Concern has been raised with regard to the safety of <span class="chemical">lorazepam</span> in this age group , especially in very - low - birth - weight ( VLBW ; < 1 , 500 g ) infants . 