This worked for me:
.current_page_item a, .current_page_item a:visited {font-weight:bold}
.page_item ul li a, .page_item ul li a:visited {font-weight:normal}
.page_item .current_page_item a, .page_item .current_page_item a:visited {font-weight:bold}
.current_page_item .page_item a, .current_page_item .page_item a:visited {font-weight:normal}
