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: Allopurinol decreased serum urate from 76 + / - 5 to 30 + / - 3 micromol / L ( P < 0 . 001 ) in saline and from 84 + / - 13 to 28 + / - 2 micromol / L in dex - treated ( P < 0 . 01 ) groups .
### Output Text:
<span class="chemical">Allopurinol</span> decreased serum <span class="chemical">urate</span> from 76 + / - 5 to 30 + / - 3 micromol / L ( P < 0 . 001 ) in saline and from 84 + / - 13 to 28 + / - 2 micromol / L in <span class="chemical">dex</span> - treated ( P < 0 . 01 ) groups . 