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: Dosage was increased from 2 . 5 mg b . d . to 5 mg b . d . at 4 weeks in patients with diastolic blood pressure greater than 90 mmHg and their further response was greater than those remaining on 2 . 5 mg b . d .
### Output Text:
Dosage was increased from 2 . 5 mg b . d . to 5 mg b . d . at 4 weeks in patients with diastolic blood pressure greater than 90 mmHg and their further response was greater than those remaining on 2 . 5 mg b . d . 