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: METHODS : Patients with a clinical diagnosis of ischemic stroke ( within 24 hours ) were consecutively allocated to receive placebo ( n = 100 ) , 1 mg / h ( low - dose ) nimodipine ( n = 101 ) , or 2 mg / h ( high - dose ) nimodipine ( n = 94 ) .
### Output Text:
METHODS : Patients with a clinical diagnosis of ischemic stroke ( within 24 hours ) were consecutively allocated to receive placebo ( n = 100 ) , 1 mg / h ( low - dose ) <span class="chemical">nimodipine</span> ( n = 101 ) , or 2 mg / h ( high - dose ) <span class="chemical">nimodipine</span> ( n = 94 ) . 