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: Multivariable logistic regression was used to estimate the odds ratio ( OR ) of pacemaker insertion associated with amiodarone use , controlling for baseline risk factors and exposure to sotalol , Class I antiarrhythmic agents , beta - blockers , calcium channel blockers , and digoxin .
### Output Text:
Multivariable logistic regression was used to estimate the odds ratio ( OR ) of pacemaker insertion associated with <span class="chemical">amiodarone</span> use , controlling for baseline risk factors and exposure to <span class="chemical">sotalol</span> , Class I antiarrhythmic agents , beta - blockers , <span class="chemical">calcium</span> channel blockers , and <span class="chemical">digoxin</span> . 