Thanks for the query. Isotretinoin(Accutane) is the preffered drug for grade 3 and recalcitrant acne. maximal cumulative dose should be around 120 to 150 mg/kg body weight. Dont take this medicine on your own and follow your doctors opinion.This drug is contraindiacted during pregmancy and it should be stopped 3 months before conception, as the drug is teratogenic.
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Avoid self medication and follow doctors advice.Hope this helps you.