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: It is concluded that when this electroencephalographic and behavioural picture is seen in drug intoxication , in the absence of significant hypoxaemia , a favourable outcome may be anticipated .
### Output Text:
It is concluded that when this electroencephalographic and behavioural picture is seen in drug intoxication , in the absence of significant hypoxaemia , a favourable outcome may be anticipated . 