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: Although most patients were receiving several drugs , Mellaril ( thioridazine ) appeared to be responsible for five cases of ventricular tachycardia , one of which was fatal in a 35 year old woman .
### Output Text:
Although most patients were receiving several drugs , <span class="chemical">Mellaril</span> ( <span class="chemical">thioridazine</span> ) appeared to be responsible for five cases of ventricular tachycardia , one of which was fatal in a 35 year old woman . 