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: Haloperidol administration ( one dose of 12 mg / kg once a week s . c . ) for 4 weeks caused an increase in vacuous chewing , tongue protrusion and duration of facial twitching observed in four weekly evaluations .
### Output Text:
<span class="chemical">Haloperidol</span> administration ( one dose of 12 mg / kg once a week s . c . ) for 4 weeks caused an increase in vacuous chewing , tongue protrusion and duration of facial twitching observed in four weekly evaluations . 