Please be sure to post back and let us know how he is doing. In the meantime, while treating him I'd keep him where he isn't overdoing so he doesn't injure himself ,and if the weather is good water therapy is excellent for helping to get the muscles in the legs strengthened. Make sure he can...
Have you ever given your Drake any niacin when he was growing up? Pekin is notorious for having niaicn deficiency even as adults. My rec would be to get him Liquid B Complex and start him on it put it over a small amount of treat so he gets a full dose. lml a day until you see full recovery then...