how to exclude admin page from add_rewrite_rule in wordpress

Try using this:

if (!is_admin()) {
    add_rewrite_rule('([A-Za-z0-9])/([A-Za-z0-9])', 'index.php/product?subcategory=$1&product=$2', 'top');
    add_rewrite_rule('([A-Za-z0-9])', 'index.php/categories/?cat=$1', 'top');
}