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: Initial dose was 50 mg and the dose was increased at monthly intervals to 100 mg , 150 mg and 200 mg daily until blood pressure normalized .
### Output Text:
Initial dose was 50 mg and the dose was increased at monthly intervals to 100 mg , 150 mg and 200 mg daily until blood pressure normalized . 