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: METHODS : We screened patients with SAH retrospectively and identified those with positive urine toxicology for cocaine or its metabolites .
### Output Text:
METHODS : We screened patients with SAH retrospectively and identified those with positive urine toxicology for <span class="chemical">cocaine</span> or its metabolites . 