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: Mean systolic blood pressure decreased 25 mmHg and mean diastolic blood pressure declined 15 mmHg after one month of timolol - hydrochlorothiazide therapy ( P less than 0 . 01 , both comparisons ) .
### Output Text:
Mean systolic blood pressure decreased 25 mmHg and mean diastolic blood pressure declined 15 mmHg after one month of <span class="chemical">timolol</span> - <span class="chemical">hydrochlorothiazide</span> therapy ( P less than 0 . 01 , both comparisons ) . 