INTRODUCTION: Isavuconazole, a broad-spectrum triazole approved by the United States Food and Drug Administration (FDA) in 2015, moderately inhibits cytochrome P450 3A4. Although antifungal agents are often used concomitantly with cyclosporine, the effect of switching from voriconazole to isavuconazole on the blood cyclosporine level remains unclear. CASE: A 63-year-old Japanese male was administered oral cyclosporine (10:00 and 21:00) for severe aplastic anemia. Following pneumonia with positive CONCLUSION: The interaction of isavuconazole with cyclosporine was weaker than that with voriconazole. Maintaining a two-hour dosing interval between isavuconazole and cyclosporine may minimize gastrointestinal drug interactions.