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: A number of small scale clinical trials have unequivocally shown that intermittent subcutaneous apomorphine injections produce antiparkinsonian benefit close if not identical to that seen with levodopa and that apomorphine rescue injections can reliably revert off - periods even in patients with complex on - off motor swings .
### Output Text:
A number of small scale clinical trials have unequivocally shown that intermittent subcutaneous <span class="chemical">apomorphine</span> injections produce antiparkinsonian benefit close if not identical to that seen with <span class="chemical">levodopa</span> and that <span class="chemical">apomorphine</span> rescue injections can reliably revert off - periods even in patients with complex on - off motor swings . 