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: The arrhythmias were temporally related to cimetidine administration , disappeared after dechallenge , and did not recur during ranitidine treatment .
### Output Text:
The arrhythmias were temporally related to <span class="chemical">cimetidine</span> administration , disappeared after dechallenge , and did not recur during <span class="chemical">ranitidine</span> treatment . 