<?
function strtrim( $str ) {
   return preg_replace('/(.+?\d)[^\d]*$/i', '$1', $str);
}

echo strtrim("item101S")."\n";
echo strtrim("paosdkpasd")."\n";
echo strtrim("23121asd")."\n";
echo strtrim("1321345+")."\n";
?>

item101
paosdkpasd
23121
1321345