The Effects of Voriconazole on Metabolism of All-Trans Retinoic Acid in the Treatment of Acute Promyelocytic Leukemia: A Case Report

All-trans retinoic acid (ATRA) is a derivative of vitamin A and is the mainstay treatment of acute promyelocytic leukemia (APL). Hypercalcemia is a rare yet important side-effect of ATRA, especially when it is used concomitantly with a medication that impedes its metabolism by inhibiting cytochrome P-450 in the liver and thus increasing the duration of exposure to ATRA. Azole antifungal drugs such as voriconazole are frequently used in patients undergoing chemotherapy due to a high incidence of fungal infections. These medications inhibit two vital enzymes of cytochrome P-450, CYP2C9 and CYP3A4, potentiating the effects of ATRA on calcium metabolism. We present a case of a nine-year-old girl who underwent chemotherapy with all-trans retinoic acid for acute promyelocytic leukemia. The patient was given an anti-fungal cover with voriconazole for extensive fungal chest infection simultaneously. She was found to have asymptomatic hypercalcemia on routine follow-up during the consolidation phase. Both medications were stopped. Subsequently, she was admitted to the ward and managed conservatively with hydration. Serum calcium levels were returned to normal within six days after stopping the combination of ATRA and voriconazole. We underscore that the use of anti-fungal medications should be limited while using ATRA. However, strict monitoring must be done when a combination of these drugs is started, if necessary.