The invention involves using a plasma to functionalize a surface of medical devices such as catheters, particularly intracardial catheters, with covalently bound thermochemically reactive groups. The surface is further contacted with a bioactive agent, particularly antithrombogenic coatings, which is thermochemically covalently coupled to the reactive group to form a therapeutically effective coating. The selected bioactive agent is then covalently bound to the surface by thermochemical reaction with the surface reactive groups. In another embodiment, the functionalizing step comprises contacting the surface with a Langmuir-Blodgett film comprising an amphipathic compound and a bioactive agent and using a plasma to covalently crosslink the Langmuir-Blodgett film to the medical device surface and to the bioactive agent. Medical devices prepared by the subject methods are also provided.