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: There were 6 cases implicating clarithromycin , 13 implicating isoniazid , and 1 case each implicating erythromycin and amoxicillin .
### Output Text:
There were 6 cases implicating <span class="chemical">clarithromycin</span> , 13 implicating <span class="chemical">isoniazid</span> , and 1 case each implicating <span class="chemical">erythromycin</span> and <span class="chemical">amoxicillin</span> . 