The present invention provides an assembly for the preparation of a medical device having a porous coating comprising hydrogen peroxide. Particularly interesting medical devices are catheters (such as urinary catheters), endoscopes, laryngoscopes, tubes for feeding, tubes for drainage, guide wires, condoms, urisheaths, barrier coatings e.g. for gloves, stents and other implants, extra corporeal blood conduits, membranes e.g. for dialysis, blood filters, devices for circulatory assistance, dressings for wound care, and ostomy bags. The coating is in particular a hydrophilic coating formed from cross-linked polyvinylpyrrolidone. In one embodiment, the assembly holds a dry catheter element in one compartment of a package and an aqueous hydrogen peroxide solution in another compartment. The solution may also comprise stabilizers, e.g. chelators, and osmolality increasing agents. The catheter for insertion in the urethra is useful for the treatment, alleviation or prophylaxis of microbial infections such as urinary tract infections (UTI).