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: VAL / HCTZ 320 / 12 . 5 and 320 / 25 mg were further investigated in a 54 - week , open - label extension .
### Output Text:
<span class="chemical">VAL</span> / <span class="chemical">HCTZ</span> 320 / 12 . 5 and 320 / 25 mg were further investigated in a 54 - week , open - label extension . 