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: After premedication with diazepam , glycopyrrolate and local anaesthesia , and induction with standard doses of ketamine , a maintenance dose of 10 - 20 microg / kg / min of ketamine proved safe and effective .
### Output Text:
After premedication with <span class="chemical">diazepam</span> , <span class="chemical">glycopyrrolate</span> and local anaesthesia , and induction with standard doses of <span class="chemical">ketamine</span> , a maintenance dose of 10 - 20 microg / kg / min of <span class="chemical">ketamine</span> proved safe and effective . 