Subtherapeutic posaconazole prophylaxis in a gastric bypass patient following hematopoietic stem cell transplantation

Purpose. A case of invasive fungal infections (IFIs) with subtherapeutic posaconazole prophylaxis in a gastric bypass patient following hematopoietic stem cell transplantation (HSCT) is reported. Summary. A 52-year-old malnourished male with a medical history of Roux-en-Y gastric bypass for obesity developed acute myelogenous leukemia and underwent allogeneic HSCT approximately 17 months later. He was admitted 1 month after HSCT for failure to thrive and initiated on parenteral nutrition due to worsening diarrhea and suspected gastrointestinal graft-versus-host disease (GI GVHD). During admission, the patient was continued on daily oral posaconazole for antifungal prophylaxis and was found to have subtherapeutic posaconazole and deficient vitamin levels, likely secondary to his gastrojejunostomy and increased gastric transit time. The oral posaconazole was altered to twice-daily dosing in an effort to increase serum drug levels and prevent IFIs. Conclusion. Patients with a history of gastric bypass are at increased risk for malabsorption of oral posaconazole and nutrients, especially following HSCT with suspected GI GVHD.