$re = '/(([a-zá-ú]+)[\.,]?\s[A-ZÃ-Úa-zá-ú]){3,}\1/m';
$str = '¡No, no, no, no, no, no, no, no, no!
No no no no no no.
No. No. No. No. No. No.';
$subst = "$1$1";
$result = preg_replace($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