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: Various data suggest that male patients who have received digoxin on a longterm basis have increased levels of serum estrogen and decreased levels of plasma testosterone and luteinizing hormone ( LH ) .
### Output Text:
Various data suggest that male patients who have received <span class="chemical">digoxin</span> on a longterm basis have increased levels of serum <span class="chemical">estrogen</span> and decreased levels of plasma <span class="chemical">testosterone</span> and luteinizing hormone ( LH ) . 