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: Suxamethonium causes prolonged apnea in patients in whom pseudocholinesterase enzyme gets deactivated by organophosphorus ( OP ) poisons .
### Output Text:
<span class="chemical">Suxamethonium</span> causes prolonged apnea in patients in whom pseudocholinesterase enzyme gets deactivated by <span class="chemical">organophosphorus ( OP ) poisons</span> . 