if the format is always ddd-dddd (d for a digit) and there is no digit in strings in front of it, then you may toggle with anydigit(drugname) and index(drugname, '-'). or you can scan the string with delimitator space and '-' and see what you get from the data.
without the regular expression handling,, the extraction of number strings is fairly straight forward in SAS9. Just compress(), keeping blank, dash and digits. Then scan() using blank and dash as delimiters.
I think it should be something like
scan( compress( original, ' -)', 'kd' ). 1, '- ' )