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 order that this syndrome might be investigated changes in mental status ( M . S . ) were correlated with serum concentrations and renal and hepatic function in 36 patients , 30 patients had no M . S . change on cimetidine and 6 had moderate to severe changes .
### Output Text:
In order that this syndrome might be investigated changes in mental status ( M . S . ) were correlated with serum concentrations and renal and hepatic function in 36 patients , 30 patients had no M . S . change on <span class="chemical">cimetidine</span> and 6 had moderate to severe changes . 