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: Using repetitive transcranial magnetic stimulation ( rTMS ) over the supplementary motor area ( SMA ) in a group of patients with advanced Parkinson disease , the authors investigated whether modulation of SMA excitability may result in a modification of a dyskinetic state induced by continuous apomorphine infusion .
### Output Text:
Using repetitive transcranial magnetic stimulation ( rTMS ) over the supplementary motor area ( SMA ) in a group of patients with advanced Parkinson disease , the authors investigated whether modulation of SMA excitability may result in a modification of a dyskinetic state induced by continuous <span class="chemical">apomorphine</span> infusion . 