Don't use pconnect. Using pconnect means connections are held open by the server process even if they're not being used. All using pconnect does is make the next request slightly faster because there's a connection already being held open for it.
Of course, that won't stop the barrage of requests in the first place .... at 25 page hits per second, if your script takes more than four seconds to run (egads!) the number of open and running connections will reach saturation all over again - there's no cure for that except increasing the allowable number of connections on the database, and server-level IP blocking as saraadmin said.
