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: METHOD : In a 6 - week random - assignment , double - blind , placebo - controlled trial ( phase A ) , haloperidol , 2 - 3 mg / day ( standard dose ) , and haloperidol , 0 . 50 - 0 . 75 mg / day ( low dose ) , were compared in 71 outpatients with Alzheimer ' s disease .
### Output Text:
METHOD : In a 6 - week random - assignment , double - blind , placebo - controlled trial ( phase A ) , <span class="chemical">haloperidol</span> , 2 - 3 mg / day ( standard dose ) , and <span class="chemical">haloperidol</span> , 0 . 50 - 0 . 75 mg / day ( low dose ) , were compared in 71 outpatients with Alzheimer ' s disease . 