Real-World Safety of Oral Isotretinoin in Patients During Sunny Months: Retrospective Cohort Study

Introduction: There is a widespread clinical practice of avoiding oral isotretinoin administration during the sunny season due to its purported photosensitizing effect. However, this approach is not supported by solid evidence. Objective: The aim of this study was to assess the safety and effectiveness of administering oral isotretinoin at a reduced daily dosage during the sunny period in a real-world clinical setting. Methods: This retrospective cohort study included all acne patients treated with oral isotretinoin at our Acne Clinic (January 2014-December 2023) who had received the drug between June and September, when UV index exceeds a threshold of 6. Conventionally, oral isotretinoin daily dosage is reduced by approximately half during these four sunny months and then increased again. We compared the occurrence of side effects or treatment discontinuation between sunny and non-sunny periods. The therapeutic response was explored in relation to the daily dosage. Results: 359 patients (61.3% males, with a mean age of 19.0 years, standard deviation (SD) 6.7) were included. Adverse events were reported by 39.2% and 28.3% of patients during the non-sunny and sunny months, respectively. The incidence of treatment discontinuation was negligible. The reduction in acne severity was independent of the daily dosage of oral isotretinoin. Conclusions: The study results support the lack of any necessity to suspend or refrain from administering oral isotretinoin during sunny seasons. The preventive reduction of its daily dosage during sunny periods does not negatively affect the drug's effectiveness. Oral isotretinoin can be taken, at a slightly reduced dosage, during sunny months.