Pharmaceutical dosage forms for controlled release producing at least a timed pulse

A delayed release coated core which produces a timed pulse release containing an active substance in its core and a polymer coating comprising an ammonio methacrylate copolymer, said core further containing a zwitterionic surfactant in an amount of from 10% to 50% relative to the amount of ammonio methacrylate copolymer in the coating, and wherein the zwitterionic surfactant is chosen from N-alkylbetaines, C-alkylbetaines, N-alkylamidobetaines and N-alkylglycines.