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: This prospective study determined the incidence of CIN for two nonionic contrast media ( CM ) , iopromide and iohexol , among 80 patients younger than 18 years and compared the rates for this complication in relation to the type and dosage of CM and the presence of cyanosis .
### Output Text:
This prospective study determined the incidence of CIN for two nonionic <span class="chemical">contrast media</span> ( <span class="chemical">CM</span> ) , <span class="chemical">iopromide</span> and <span class="chemical">iohexol</span> , among 80 patients younger than 18 years and compared the rates for this complication in relation to the type and dosage of <span class="chemical">CM</span> and the presence of cyanosis . 