Dosage Guidelines: Extracorporeal Photochemotherapy (Photopheresis)

To the Editor.—  Extracorporeal photochemotherapy (photopheresis) has been approved for the treatment of cutaneous T-cell lymphoma. During the clinical trial that documented the effectiveness of this therapy,¹ patients were treated with a minimum of 0.6 mg/kg crystalline 8-methoxypsoralen (8-MOP). Proper dosing was confirmed by serum levels obtained at 2 hours, demonstrating a level of 100 ng/mL or greater.Now that a liquid formulation of 8-MOP is available (Oxsoralen-ULTRA, Elder Pharmaceuticals), we have found dosing to be more reliable and more convenient when followed as outlined in this communiqué.Rather than measuring serum levels, we have converted to measuring 8-MOP levels in the treatment bag of photopheresis. The treatment bag contains a 240-mL buffy coat, 200 mL of psoralen-rich plasma, and 200 mL of saline. The rationale is that the serum level represents a single point in time, whereas the treatment bag contains serum collected over several pheresis cycles. Values