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 63 year - old Caucasian man on metoprolol 200 mg / day for stable coronary artery disease was prescribed a 90 - day course of oral terbinafine 250 mg / day for onychomycosis .
### Output Text:
A 63 year - old Caucasian man on <span class="chemical">metoprolol</span> 200 mg / day for stable coronary artery disease was prescribed a 90 - day course of oral <span class="chemical">terbinafine</span> 250 mg / day for onychomycosis . 