How to avoid duplicating tabs with openURL?

I have an openURL call and every time I press it IE8 opens a new tab to open the page. Is there any way to specify the URL to avoid this? Maybe just have IE show the tab that already has that page, or force IE to just have one tab so it always overwrites?

I’m not entirely sure, but I don’t think there is anything you can do unless IE itself has some sort of setting for opening a new page in a new or existing tab.