Is taking 20 mgs of isotretinoin one day and 40 mgs the next day a normal recommendation?

I'm 42. I took a course of isotretinoin 7 years ago. I'm doing a second course. I have taken 20 mgs a day for 21 weeks with virtually no side effects - bit of dry lips, nothing else. I want it over. Nurse suggested taking 20 one day and 40 next as a regular pattern to get to end and side effects away. I have not had any new spots for around 17 weeks now.

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