You can use ketoconazole shampoo for dandruff or seborrheic dermatitis twice a week for 2 to 4 weeks, and then once every 1 to 2 weeks to prevent symptoms from returning. If you have been using it every other day, consider reducing the frequency to avoid potential irritation.
National Health Service (NHS) nizoralshampoo.co.uk
Duration of Ketoconazole Use
General Guidelines
Dandruff and Seborrheic Dermatitis: Use ketoconazole shampoo twice a week for 2 to 4 weeks. After symptoms improve, continue using it once every 1 to 2 weeks to prevent recurrence.
Pityriasis Versicolor: Apply the shampoo once daily for up to 5 days.
Psoriasis: Consult your doctor for specific recommendations, as ketoconazole may not be the primary treatment.
Daily Use Considerations
Daily Washing: If you wash your hair every day, you can still use ketoconazole shampoo as part of your routine. However, it is advisable to alternate with a regular shampoo to avoid potential irritation.
Long-Term Use: Some individuals may use ketoconazole shampoo every 1 to 2 weeks for maintenance after initial treatment.
Monitoring and Consultation
Consult Your Doctor: If symptoms persist after 4 weeks of use, or if you experience side effects, consult your healthcare provider for further advice.
Side Effects: Be aware of potential side effects like skin irritation or changes in hair texture. If these occur, discuss with your doctor whether to adjust your usage.
Following these guidelines will help ensure effective treatment while minimizing the risk of irritation.

Until you are sure your infection is cleared up. Talk with your dermatologist.