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 patient developed a severe cholinergic syndrome from the use of echothiophate iodide ophthalmic drops , presented with profound muscle weakness and was initially given the diagnosis of myasthenia gravis .
### Output Text:
A patient developed a severe cholinergic syndrome from the use of <span class="chemical">echothiophate iodide</span> ophthalmic drops , presented with profound muscle weakness and was initially given the diagnosis of myasthenia gravis . 