8-Methoxypsoralen (8-MOP), Serum
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
8-Methoxypsoralen (8-MOP) is a photosensitizing drug given to patients who are undergoing extracorporeal photopheresis (ECPP) for the palliative treatment of cutaneous T-cell lymphoma (Sezary syndrome and mycosis fungoides). 8-MOP is also used in the ultraviolet treatment (PUVA) of severe psoriasis.
The process of leukopheresis removes leukocytes from the blood so that therapeutic doses of long-wavelength ultraviolet light (UVA) can reach the 8-MOP-sensitized leukocytes; after exposure of the blood to UVA, the leukophoretic process is completed by returning the treated blood to the patient. 8-MOP and UVA act together to produce the desired beneficial effect on the patient, namely the reduction in the growth of specific lymphocyte subpopulations. ECPP stimulates an immune reaction that results in large numbers of damaged T-cells being eliminated from the circulation and the tissue reservoirs shortly after ECPP; patients appear to exhibit a vaccine-like response to the reinfused cells, with, in the best scenario, a lasting suppression of malignant T-cells.
For the UVA treatments to be effective, optimal levels of 8-MOP must be present in the patient's blood. Because 8-MOP exhibits a significant first pass hepatic effect, there is considerable intra-individual variation in 8-MOP blood levels. Because of these variations, 8-MOP blood levels should be measured on a periodic basis to ensure that optimal 8-MOP levels are present in patients undergoing ECPP and PUVA. Optimal response to therapy is achieved when the serum concentration of 8-MOP is in the range of 50 to 125 ng/mL.
Monitoring adequacy of blood levels during extracorporeal photopheresis.
Blood levels of 8-methoxypsoralen must be within the concentration range of 50 to 125 ng/mL during phototherapy in order for the drug to bind to T-cells in adequate concentration to ensure their destruction during photopheresis.
The clinical effect desired will not be achieved if the blood level is <50 ng/mL during phototherapy.
Levels >125 ng/mL provide no additional benefit and increase the likelihood of toxic effects.
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
8-Methoxypsoralen is light-sensitive. Protect the specimen from direct exposure to intense light for prolonged periods of time. Wrap the specimen in foil to protect it during shipping.
Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.
Clinical References Provides recommendations for further in-depth reading of a clinical nature
Gasparro F: Use of psoralen during photopheresis. Photopheresis Review, Johnson and Johnson Company