Blood Levels

To be effective these photochemotherapies require that therapeutic levels of 8-MOP must be present. Exact values for therapeutic efficacy in the different diseases that have been treated are not known. However, studies have indicated that problem PUVA patients (i.e., those who do not respond) often have low or barely detectable blood levels of 8-MOP. YUPL has provided a fee-for-service analysis of 8-MOP blood levels since 1988. More than 5000 blood levels have been analyzed. Thus, the most extensive database of 8-MOP blood levels in patients receiving photochemotherapy has been established. The primary observation is that 8-MOP is not reproducibly bioavailable. Significant variations (both inter- and intraindividual) have been demonstrated (see Figure below). Furthermore, there is little correlation between ingested dose and the ultimate blood level achieved. It is not uncommon for patients to have less than 50 ng/mL or undetectable levels of 8-MOP in their blood. If a patient is not responding to PUVA, it is very likely that their 8-MOP level is low (see Walther T & Haustein U-F, 8-Methoxypsoralen serum levels in poor responders to photochemotherapy. Intl J Dermatol 30: 516-518 (1991)).