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: However , additional important untoward effects of heparin therapy include heparin - induced thrombocytopenia , heparin - associated osteoporosis , eosinophilia , skin reactions , allergic reactions other than thrombocytopenia , alopecia , transaminasemia , hyperkalemia , hypoaldosteronism , and priapism .
### Output Text:
However , additional important untoward effects of <span class="chemical">heparin</span> therapy include <span class="chemical">heparin</span> - induced thrombocytopenia , <span class="chemical">heparin</span> - associated osteoporosis , eosinophilia , skin reactions , allergic reactions other than thrombocytopenia , alopecia , transaminasemia , hyperkalemia , hypoaldosteronism , and priapism . 