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: A patient with transfusion - dependent thalassemia was undergoing home intravenous desferrioxamine ( DFX ) treatment by means of a totally implanted system because of his poor compliance with the nightly subcutaneous therapy .
### Output Text:
A patient with transfusion - dependent thalassemia was undergoing home intravenous <span class="chemical">desferrioxamine</span> ( <span class="chemical">DFX</span> ) treatment by means of a totally implanted system because of his poor compliance with the nightly subcutaneous therapy . 