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: We describe a previously healthy 32 - year - old woman who developed a life - threatening muscle spasm and secondary ventilation difficulties following a preoperative injection of suxamethonium .
### Output Text:
We describe a previously healthy 32 - year - old woman who developed a life - threatening muscle spasm and secondary ventilation difficulties following a preoperative injection of <span class="chemical">suxamethonium</span> . 