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: In a random fashion , they received cimetidine 200 mg iv on one day , and on the other , a pretreatment of diphenhydramine 40 mg iv with cimetidine 200 mg iv .
### Output Text:
In a random fashion , they received <span class="chemical">cimetidine</span> 200 mg iv on one day , and on the other , a pretreatment of <span class="chemical">diphenhydramine</span> 40 mg iv with <span class="chemical">cimetidine</span> 200 mg iv . 