I am trying to use preg_replace but my regex ability isn't the best.

I've got to remove all newlines from a string unless it starts with a number followed by a coma i.e. "1234,"

I came up with
$newstring = preg_replace('/(?:\n|\r\n)(?:[^0-9]+[^,])/', ' ', $oldstring);
Which seems to work until I notice a new line that starts "123 Kg".

What am I doing wrong?