$re = '/Title:.*\r?\n(?:(?!.*Database).*\r?\n)+.*\r?\n/';
$str = '[Title: irrelevant information]
[irrelevant information]
[irrelevant information]
[irrelevant information]
[irrelevant information]
[irrelevant information]
[irrelevant information]
[irrelevant information]
[irrelevant information]
[Database: irrelevant information]
[relevant text relevant text relevant text relevant text relevant text relevant text relevant text relevant text relevant text relevant text relevant text relevant text relevant text relevant text relevant text relevant text relevant text relevant text relevant text relevant text relevant text relevant text relevant text relevant text relevant text relevant text relevant text relevant text relevant text relevant text relevant text relevant text relevant text relevant text relevant text relevant text relevant text relevant text relevant text relevant text relevant text relevant text relevant text relevant text relevant text relevant text relevant text relevant text relevant text relevant text relevant text relevant text relevant text relevant text relevant text relevant text relevant text relevant text --> for multiple paragraphs]';
$subst = "";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php