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: Given that sympathetic neural dominance exhibits a similar developmental pattern , and given that clonidine induces sympathetic withdrawal and bradycardia , we hypothesized that clonidine ' s developmental effects on cardiac rate and ultrasound production would mirror each other .
### Output Text:
Given that sympathetic neural dominance exhibits a similar developmental pattern , and given that <span class="chemical">clonidine</span> induces sympathetic withdrawal and bradycardia , we hypothesized that <span class="chemical">clonidine</span> ' s developmental effects on cardiac rate and ultrasound production would mirror each other . 