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: Simultaneous administration of morphine with metamizol resulted in a markedly antinociceptive potentiation and an increasing of the duration of action after a single ( 298 + / - 7 vs . 139 + / - 36 units area ( ua ) ; P < 0 . 001 ) and repeated administration ( 280 + / - 17 vs . 131 + / - 22 ua ; P < 0 . 001 ) .
### Output Text:
Simultaneous administration of <span class="chemical">morphine</span> with <span class="chemical">metamizol</span> resulted in a markedly antinociceptive potentiation and an increasing of the duration of action after a single ( 298 + / - 7 vs . 139 + / - 36 units area ( ua ) ; P < 0 . 001 ) and repeated administration ( 280 + / - 17 vs . 131 + / - 22 ua ; P < 0 . 001 ) . 