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: In pooled follow - up data for 768 antithrombotic users , presence of MB at baseline was associated with a substantially increased risk of subsequent ICH ( OR , 12 . 1 ; 95 % CI , 3 . 4 - 42 . 5 ; P < 0 . 001 ) .
### Output Text:
In pooled follow - up data for 768 antithrombotic users , presence of MB at baseline was associated with a substantially increased risk of subsequent ICH ( OR , 12 . 1 ; 95 % CI , 3 . 4 - 42 . 5 ; P < 0 . 001 ) . 