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: Patients received up to 3 doses / day of 50 mg DCF or 2 . 5 mg / 24 h transdermal GTN for the first 3 days of the cycle , according to their needs .
### Output Text:
Patients received up to 3 doses / day of 50 mg <span class="chemical">DCF</span> or 2 . 5 mg / 24 h transdermal <span class="chemical">GTN</span> for the first 3 days of the cycle , according to their needs . 