From vitamin a to Roaccutane

Hello. I am suffering from fairly severe acne and have been taking a high dose vitamin a supplement for a couple of weeks, but have reluctantly decided to cut my losses and go for another course of Roaccutane. I have already taken three courses, the last of which was about 4-5 years ago, and since then I have managed to control the subsequent (inevitable) relapse with a retinyl palmitate supplement; bearing this in mind, I have recently attempted to tackle this present bout with the supplement, only in much higher doses as is it far more severe (300,000iu per day retinyl palmitate - following extensive research). I have an appointment with the dermatologist a week tomorrow and wanted to know whether I would have to allow a certain amount of time between coming off the vitamin a and starting a course of Roaccutane. I would very much appreciate a reply as I am pretty desperate; my livelihood depends on me having relatively clear skin and I am getting progressively more depressed as time goes on. Having decided to ask for a fourth course of Roaccutane, I want to be in a position to take it as soon as possible. Many thanks.