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: After the withdrawal of VPA therapy , our patient showed a significant weight loss , a decrease of body mass index , and normalization of metabolic and endocrine parameters ; moreover , ultrasound measurements showed a complete normalization .
### Output Text:
After the withdrawal of <span class="chemical">VPA</span> therapy , our patient showed a significant weight loss , a decrease of body mass index , and normalization of metabolic and endocrine parameters ; moreover , ultrasound measurements showed a complete normalization . 