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 50 mg higher methadone dose was associated with a 1 . 2 ( 95 % CI 1 . 1 to 1 . 4 ) times higher odds for syncope .
### Output Text:
A 50 mg higher <span class="chemical">methadone</span> dose was associated with a 1 . 2 ( 95 % CI 1 . 1 to 1 . 4 ) times higher odds for syncope . 