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: Intravenous administration of a single 50 - mg bolus of lidocaine in a 67 - year - old man resulted in profound depression of the activity of the sinoatrial and atrioventricular nodal pacemakers .
### Output Text:
Intravenous administration of a single 50 - mg bolus of <span class="chemical">lidocaine</span> in a 67 - year - old man resulted in profound depression of the activity of the sinoatrial and atrioventricular nodal pacemakers . 