Words that contain 'pn' and end in 'xy'

Oh dear, just 3 words has been discovered for this particular combination.

10 letter words

  • pneumopexy

12 letter words

  • pneumonopexy

15 letter words

  • costopneumopexy

How many letters are in the largest word from this list?
There are 15 characters in the word 'costopneumopexy', making it the longest word on this list.

In total, how many words are available using these specific combinations of letters?
There are up to a maximum of 3 entries that cover all variations.