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 , use of BZDs / RDs was associated with dizziness , inability to sleep after awaking at night and tiredness in the mornings during the week prior to admission and with stronger depressive symptoms measured at the beginning of the hospital stay .
### Output Text:
However , use of <span class="chemical">BZDs</span> / RDs was associated with dizziness , inability to sleep after awaking at night and tiredness in the mornings during the week prior to admission and with stronger depressive symptoms measured at the beginning of the hospital stay . 