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: Sixty percent of the males developed breast changes or impotence while taking cimetidine and in all cases these changes disappeared when cimetidine was replaced by ranitidine .
### Output Text:
Sixty percent of the males developed breast changes or impotence while taking <span class="chemical">cimetidine</span> and in all cases these changes disappeared when <span class="chemical">cimetidine</span> was replaced by <span class="chemical">ranitidine</span> . 