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: OBJECTIVE : This study investigated the efficacy and tolerability of valsartan ( VAL ) or hydrochlorothiazide ( HCTZ ) - monotherapy and higher - dose combinations in patients with essential hypertension .
### Output Text:
OBJECTIVE : This study investigated the efficacy and tolerability of <span class="chemical">valsartan</span> ( <span class="chemical">VAL</span> ) or <span class="chemical">hydrochlorothiazide</span> ( <span class="chemical">HCTZ</span> ) - monotherapy and higher - dose combinations in patients with essential hypertension . 