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 with CHF on amiodarone may suffer serious morbidity and mortality from hypothyroidism , and thus may deserve closer follow up for thyroid stimulating hormone ( TSH ) levels .
### Output Text:
Patients with CHF on <span class="chemical">amiodarone</span> may suffer serious morbidity and mortality from hypothyroidism , and thus may deserve closer follow up for thyroid stimulating hormone ( TSH ) levels . 