I understand how frustrating a persistent oily scalp and dandruff can be, especially after finishing a course of Isotroin. Since you have already taken this medication (isotretinoin) for four months and are using ketoconazole shampoo, it is important not to start any new oral tablets without your dermatologist's guidance. Sometimes, a low-dose maintenance course of isotretinoin is considered, but this requires close medical supervision. For now, continue with the ketoconazole shampoo, allowing it to sit on your scalp for five minutes before rinsing. Please schedule a follow-up with your doctor to discuss safe next steps for your scalp care.