Nanoemulsion containing 8-methoxypsoralen for topical treatment of dermatoses: Development, characterization and ex vivo permeation in porcine skin.

Oral therapy with 8-methoxypsoralen (8-MOP) may cause major side effects, whereas the topical treatment might not be much effective due to the low penetration induced by typical formulations. Therefore, the objectives of this work are the development and characterization of a nanoemulsion (NE) containing 8-MOP together with an ex vivo permeation study, monitored by a validated HPLC-Fluo method, to determine the amount of drug retained in viable skin (epidermis (E) and dermis (D)) and in stratum corneum (SC). The optimized conditions for NE formulation were achieved by full factorial designs (25 and 32): 60 s and 60% of ultrasound time and potency, respectively; 10 mL of final volume; 2% v/v of oil phase (clove essential oil); and 10% m/v of Poloxamer 407. The NE showed mean droplet diameter of 24.98 ±â€¯0.49 nm, polydispersity index (PDI) of 0.091 ±â€¯0.23, pH values of 6.54 ±â€¯0.06, refractive index of 1.3525 ±â€¯0.0001 and apparent viscosity of 51.15 ±â€¯3.66 mPa at 20 °C. Droplets with nanospherical diameters were also observed by transmission electron microscopy (TEM). Ex vivo permeation study showed that 8.5% of the applied 8-MOP dose permeated through the biological membranes, with flux (J) of 1.35 µg cm-2 h-1. The drug retention in E + D and in SC was 10.15 ±â€¯1.36 and 1.95 ±â€¯0.71 µg cm-2, respectively. Retention in viable skin induced by the NE was almost two-fold higher than a compounded cream (5.04 ±â€¯0.30 µg cm-2). These results suggested that the developed NE is a promising alternative for 8-MOP topical therapy when compared to commercial formulations.

Simultaneous Determination of Six Coumarins in Rat Plasma and Metabolites Identification of Bergapten in Vitro and in Vivo.

Coumarins are abundant in Umbelliferae and Rutaceae plants possessing varied pharmacological activities. The objectives of this study are to develop and validate the method for determination of six coumarins in rat plasma by liquid chromatography coupled with tandem mass spectrometry (LC-MS) and identify the metabolites of bergapten by ultra-high-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (UHPLC-Q-TOF-MS), respectively. Data-dependent acquisition mode (DDA) was applied to trigger enhanced product ion (EPI) scans by analyzing multiple reaction monitoring (MRM) signals. An efficient data processing method "key product ions (KPIs)" was used for rapid detection and identification of metabolites as an assistant tool. The time to reach the maximum plasma concentration ( Tmax) for the six compounds ranged from 1 to 6 h. A total of 24 metabolites of bergapten were detected in vitro and in vivo. The results could provide a basis for absorption and metabolism of coumarins.

Simultaneous determination of scopoletin, psoralen, bergapten, xanthotoxin, columbianetin acetate, imperatorin, osthole and isoimperatorin in rat plasma by LC-MS/MS for pharmacokinetic studies following oral administration of Radix Angelicae Pubescentis extract.

A rapid and sensitive bioassay based on liquid chromatography tandem mass spectrometry (LC-MS/MS) has been developed and validated for the simultaneous determination of eight coumarins in rat plasma. The liquid-liquid extraction method with ethyl acetate was used to prepare the plasma samples after addition of warfarin as an internal standard (IS). Chromatographic separation was performed on an Eclipse plus C18 column (100mm×4.6mm, 1.8µm) using gradient elution when 1mM ammonium acetate aqueous solution - acetonitrile was used as the mobile phase. The lower limit of quantitation (LLOQ) of each coumarin was lower than 2.16ngmL(-1). Intra-day and inter-day precisions were less than 15%. The accuracies were in the range of 88.9-117%. The mean recoveries of coumarins and IS were higher than 84%. The method was successfully applied to a pharmacokinetic study of eight coumarins in rats after oral administration of radix angelicae pubescentis.

[Phamacokinetic study of bergapten in rats plasma by LC-MS/MS].

OBJECTIVE: To determine bergapten's concentration in plasma and observe its pharmacokinetics in rats using a combined LC-MS/MS analytical method. METHOD: Blood samples were separated on a Hypersil ODS column (4.6 mm x 250 mm, 5 mm) at a temperature of 30 degrees C, and mobile phase consisted of water and methanol (22.5: 77.5) at a flow rate of 0.8 mL x min(-1). RESULT: The methodological study showed a good linear relationship of 8.12-162.4 g x L(-1) (r = 0.9999). The inner and inter-days relative standard deviations were both less than 10% , indicating legitimate precise and accuracy to the requirement of biological sample analysis. CONCLUSION: The method is suitable for in vivo quantitative analysis for bergapten due to its accuracy, sensitivity and specificity. The pharmacokinetic process in rats forms a two-compartment model with first-order absorption.

Simultaneous determination of pimpinellin, isopimpinellin and phellopterin in rat plasma by a validated UPLC-MS/MS and its application to a pharmacokinetic study after administration of Toddalia asiatica extract.

A rapid and selective ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method was developed for simultaneous determination of three bioactive coumarins of Toddalia asiatica extract including pimpinellin, isopimpinellin and phellopterin in rat plasma for the first time. Phenacetin was used as the internal standard (IS). Plasma samples were extracted by liquid-liquid extraction with methyl tert-butyl ether. The chromatographic separation was carried out on an ACQUITY UPLC™ BEH C18 column with an isocratic mobile phase consisting of methanol-5 mmol/L ammonium acetate (65:35, v/v). The detection was performed on a triple quadrupole tandem mass spectrometer by multiple reaction monitoring (MRM) via electrospray ionization (ESI) source with positive ionization mode. The method was linear for all analytes over investigated range with all correlation coefficients greater than 0.9942. The lower limits of quantification (LLOQ) were 25.0 ng/mL for pimpinellin, 10.0 ng/mL for isopimpinellin and 5.00 ng/mL for phellopterin. The intra- and inter-day precision (RSD%) was within 12% and the accuracy (RE%) ranged from -2.3% to 5.5%. The rapid and sensitive method was fully validated and successfully applied to the pharmacokinetic study of pimpinellin, isopimpinellin and phellopterin in rats following oral administration of Toddalia asiatica extract.

Effect of polyamidoamine dendrimer G3 and G4 on skin permeation of 8-methoxypsoralene--in vivo study.

In the present study we have assessed the ability of (PAMAM) dendrimers G3 and G4 to facilitate transdermal delivery of 8-methoxypsoralen (8-MOP) in vivo. In vitro study using Franz diffusion cell revealed an enhanced transdermal flux for 8-MOP in complex with G3 and G4 dendrimer in relation to standard 8-MOP solution. In present study in vivo skin permeation potential of 8-MOP complex with G3 and G4 PAMAM dendrimer was assessed using confocal laser scanning microscopy (CLSM), which revealed an enhanced permeation of the 8-MOP to the deeper layers of the skin and significantly higher concentration in comparison with standard 8-MOP solution. Skin tissue 8-MOP concentration, evaluated by HPLC indicates that G3 and G4 PAMAM application significantly increase 8-MOP skin deposition in comparison with standard 8-MOP solutions after 1 and 2h. G4 appeared to be a more effective 8-MOP penetration enhancer than G3 PAMAM. Our results suggest the feasibility of G3 and G4 PAMAM dendrimers for transdermal delivery of 8-MOP resulting in better skin permeation and higher concentration of 8-MOP in epidermis and dermis of the drug that could help to improve effectiveness and safety of PUVA therapy.

High plasma levels of 8-methoxypsoralen following bath water delivery in dermatological patients.

With respect to the clinical advantages known for bath PUVA therapy, it was of interest to compare the plasma levels of 8-methoxypsoralen (8-MOP) in bath therapy with those after oral administration for a better insight into the pharmacokinetics of 8-MOP following different modes of application. Considerable high plasma levels of 8-MOP were observed after bath therapy with interindividual variability. The half-life of plasma 8-MOP was markedly shorter after bath PUVA than after oral application. The pharmacokinetic profile of 8-MOP differs according to the mode of application.

Spatial distribution of 8-methoxypsoralen penetration into human skin after systemic or topical administration.

AIMS: Photochemotherapy employing psoralens combined with UVA irradiation (PUVA) is a standard therapy for a variety of dermatoses. Psoralens can be administered orally or topically in the form of bath or cream preparations. Recommendations for the time of UVA irradiation are mainly based on the time course of minimal phototoxic doses. However, the time course and depth of skin penetration of psoralens is not well characterized. METHODS: We assessed the time course of 8-MOP concentrations in horizontal epidermal and dermal skin sections in 10 patients undergoing oral (n = 3), cream (n = 4) and bath (n = 3) PUVA therapy. Punch biopsies (4 mm) were taken from "healthy" skin sites. A highly sensitive LC-MS-MS method was employed for 8-MOP analysis. RESULTS: Epidermal concentrations following cream or bath were highest at the end of the application period (time zero) when irradiation is performed. At this time, 8-MOP cream provided significantly higher epidermal concentrations (mean +/- s.e. mean 128.0 +/- 22.6 pg mm-3; 95% CI: 77.6, 178.4) than oral 8-MOP (27.0 +/- 25.3 pg mm-3; 95% CI: 29.3, 83.3 at 1 h; P = 0.025). Conversely, concentrations in the papillary dermis were significantly higher with oral 8-MOP (20.2 +/- 3.1 and 16.2 +/- 2.2 pg mm-3 at 1 and 2 h, respectively) than with 8-MOP cream (7.1 +/- 2.8 and 8.4 +/- 2.0 pg mm-3 time zero and 0.5 h, respectively; P = 0.020 and 0.045, respectively) or bath (8.8 +/- 3.1 and 7.7 +/- 2.2 pg mm-3; P = 0.050 and 0.039, respectively). The observed time courses of 8-MOP concentrations correspond to time courses of photosensitivity found previously with the different treatment modalities. CONCLUSIONS: The higher epidermal 8-MOP concentrations found after topical 8-MOP may explain the lower UVA doses needed with the topical route. These results suggest that topical 8-MOP may be superior in patients where the pathology is localized in the epidermis. In sclerosing diseases, which mainly affect the dermis oral PUVA might be advantageous because dermal concentrations are highest with this route of administration.

Time course of 8-methoxypsoralen concentrations in skin and plasma after topical (bath and cream) and oral administration of 8-methoxypsoralen.

BACKGROUND: The combination of 8-methoxypsoralen with ultraviolet A exposure (PUVA therapy) is a standard treatment for a variety of dermatoses. The following three variants have been described: oral, bath, or cream PUVA. To achieve optimal therapeutic effects, ultraviolet A irradiation should be performed at the time of maximum photosensitivity, that is, at the time of maximum 8-methoxypsoralen tissue concentrations. METHODS: To further specify this point of time, we assessed the concentration-time courses of 8-methoxypsoralen in the skin after oral, bath, and cream administration of 8-methoxypsoralen in a 3-way crossover microdialysis study of 8 healthy subjects. RESULTS: Tissue concentrations after oral administration of 0.6 or 1 mg/kg 8-methoxypsoralen were low (peak plasma concentration range, 1.7-6.6 ng/ml) compared with topical administration for which maximum concentrations of 200 to 520 ng/ml and 720 to 970 ng/ml were achieved with 0.1% 8-methoxypsoralen cream and 3 mg/L 8-methoxypsoralen bath, respectively. Plasma concentrations after oral 8-methoxypsoralen, however, were up to 1000-fold higher than those found after topical application. With both topical applications, the tissue peak concentration uniformly occurred in the first 20 minutes after the end of the application time. In contrast, the time to reach the tissue peak concentration after oral administration ranged from 1 to 4 hours. CONCLUSIONS: The time course of tissue concentrations corresponds closely with the time course of minimal phototoxic doses found in previous studies. Because tissue concentrations after topical administration of 8-methoxypsoralen (bath and cream) were high compared with plasma concentrations and because they were less variable and occurred at better predictable time points than those after oral administration, we suggest that topical PUVA is superior to systemic PUVA, at least from a pharmacokinetic point of view.

Plasma and skin concentration of 5-methoxypsoralen in psoriatic patients after oral administration.

The aim of this work was to investigate the distribution of 5-methoxypsoralen in the skin after oral administration of the drug and to examine the correlation between skin and plasma concentrations. 5-Methoxypsoralen skin concentration was measured in both healthy and psoriatic sites of 10 psoriatic patients after single and multiple oral doses. The results obtained show that 5-methoxypsoralen accumulates at higher levels in the more external layers of the skin after oral administration. The high affinity of drug for the stratum corneum was confirmed by in vitro skin affinity measurements. The concentration of 5-methoxypsoralen in the skin was similar in both psoriatic and healthy sites, indicating that the pathology does not influence drug distribution in the skin. After single dose administration, a linear correlation was found between skin and plasma drug concentration. After multiple dose administration, drug concentration in the skin was fairly constant despite the variable plasma concentrations in different subjects.

Kinetics and dose-response of photosensitivity in cream psoralen plus ultraviolet A photochemotherapy: comparative in vivo studies after topical application of three standard preparations.

BACKGROUND: Topical photochemotherapy with bath psoralen plus ultraviolet (UV) A irradiation (PUVA) has been developed to reduce possible side-effects of oral PUVA therapy. Although the efficacy of bath PUVA therapy appears to be similar to oral PUVA therapy, provision of bathing facilities has obvious economic, logistic and sanitary implications. Cream PUVA therapy has recently been developed as a variation of topical PUVA. OBJECTIVES: To understand the photobiological effects and to increase the safety and effectiveness of this novel topical PUVA therapy, we assessed the kinetics and dose-response of phototoxicity of 8-methoxypsoralen (8-MOP) cream in order to develop a treatment schedule for this treatment option. METHODS: Ninety-eight patients (63 men and 35 women) undergoing cream PUVA therapy were studied. The phototoxic properties of topically applied 8-MOP in three different water-in-oil creams as vehicles were assessed. In a dose-response study, four concentrations of 8-MOP cream (0.0006-0.005%) were used for determination of the minimal phototoxic dose (MPD). The kinetics of photosensitization were tested by determination of MPDs after different application times of 8-MOP cream (10, 20, 30 and 60 min). The persistence of phototoxicity was assessed by UVA exposure at defined time intervals after application of 8-MOP cream (0, 30, 60 and 120 min). RESULTS: The concentration required to produce sufficient but not undue photosensitization of the skin was 0.001% 8-MOP. The duration of application leading to the lowest MPD was 30 min. Greatest photosensitization was achieved when UVA irradiation was performed between 0 and 30 min after 8-MOP removal. These findings showed no significant difference between the three vehicles used. CONCLUSIONS: Based on our data we recommend application of 0.001% 8-MOP in a water-in-oil cream for 30 min. Irradiation with UVA should be performed within 30 min after removal of 8-MOP cream, as there is a rapid decrease in photosensitivity thereafter.

Pharmacokinetic behaviour of sublingually administered 8-methoxypsoralen for PUVA therapy.

BACKGROUND: Conventional oral PUVA therapy is hampered by large inter- and intraindividual variations in the bioavailability of 8-methoxypsoralen (8-MOP), caused by its low solubility in the gastrointestinal juices and large interindividual differences in hepatic metabolism rate (hepatic first pass). AIMS: New galenic formulations of 8-MOP based on solid dispersions, suspensions, and saturated solutions containing penetration enhancers were developed for sublingual administration, a drug delivery route which avoids the hepatic first pass metabolism. METHODS: Solubility properties of 8-MOP were tested in 22 potential penetration enhancers and solubilizers. Following preliminary in vivo tests of 13 sublingual 8-MOP formulations, five were administered to groups of volunteers at a nominal dose of 0.6 mg/kg body weight: two solid dispersions based on PEG 1540 (with and without Xylitol); a solution in Labrasol (glyceryl and PEG-8 caprylate/caprate), PEG 400, Transcutol (ethoxydiglycol) (1:1:1); a micronized suspension in sorbitol, water, ethanol, propylene glycol (ca. 3:1:1:5 w/v); and Oxsoralen capsules. Pharmacokinetic behaviour of 8-MOP was examined in serum; samples were analysed by HPLC. Photosensitivity was measured in seven subjects. RESULTS: The peak of maximum 8-MOP concentration in blood was sharp, rapid and reproducible: tmax of 8-MOP in blood averaged 23+/-3 min, independent of the particular formulation. Cmax was higher when 8-MOP was presented in dissolved form (solution and capsule formulations, 85+/-29 and 85+/-35 ng/ml, respectively) and lowest with the suspension (42+/-15 ng/ml). Photosensitivity peaked reproducibly at 45 min. post dosing. CONCLUSIONS: Sublingual PUVA therapy is suitable for patients with skin types I and II, in particular patients who are less suitable candidates for standard PUVA therapy (due to hepatic, renal, or cardiac insufficiency) or who have experienced side effects with standard PUVA.

Psoralen-ultraviolet A-induced erythema: sensitivity correlates with the concentrations of psoralen in suction blister fluid.

Since the advent of psoralen-ultraviolet A (PUVA) therapy, the value of plasma 8-methoxypsoralen (8-MOP) concentrations to predict PUVA-induced erythema has been widely investigated. Plasma 8-MOP concentrations have not been proportional to, and cannot alone predict, the degree of PUVA-induced erythema. We assumed that PUVA-induced erythema was related more closely to psoralen concentrations in the skin tissue rather than those within blood vessels. This study was designed to investigate the correlations between the 8-MOP concentrations in suction blister fluid (SBF) and in plasma, with the degree of PUVA-induced erythema. 8-MOP concentrations in plasma and SBF were measured in 15 vitiligo patients and 11 volunteers. Blood and SBF samples were collected 2 h after taking 8-MOP, and 8-MOP concentrations in plasma and SBF were quantified using reverse-phase high-performance liquid chromatography. Eleven volunteers were phototested using a series of doses of ultraviolet A at the time of sampling. The erythema responses were estimated visually to determine the minimal phototoxic dose (MPD). SBF 8-MOP concentrations showed a weak positive correlation with plasma 8-MOP concentrations, which means that we could not predict the exact SBF 8-MOP concentrations using the plasma 8-MOP concentrations. The MPD showed a better correlation with the log of the SBF 8-MOP concentration than with that of the plasma 8-MOP concentration. These results show that plasma 8-MOP concentration cannot represent the exact SBF 8-MOP concentration, and that SBF 8-MOP concentrations, which are representative of the skin tissue 8-MOP level, are more closely related to the erythemal sensitivity during PUVA therapy.

Carcinogenic risk of bath PUVA in comparison to oral PUVA therapy.

The potential carcinogenic risk of bath PUVA therapy was compared to that of systemic (oral) PUVA. An analysis of the epidemiological data on cancer risk following bath PUVA with trimethylpsoralen does not support the conclusion that bath PUVA per se is less carcinogenic than systemic PUVA with 8-methoxypsoralen (8-MOP). Pharmacokinetic studies indicate that both the concentration of 8-MOP in the target organ for PUVA carcinogenicity (skin) at the relevant time point (time point of UVA irradiation) and the extents of biological effects in the skin are comparable following bathwater or systemic 8-MOP administration. Furthermore, the therapeutic effects of PUVA arise from the same photochemical reaction mechanisms as do the carcinogenic effects. Theoretically, the ratio of (desired) cytotoxic versus (undesired) mutagenic effects could increase with increasing efficiency of the PUVA therapy itself. On the basis of the available evidence, it is concluded that all forms of PUVA therapy, independently of the route of 8-MOP administration, contribute to a small but dose-dependent increase in nonmelanoma skin cancer risk.

Measurement of 5-methoxypsoralen and 8-methoxypsoralen in saliva of PUVA patients as a noninvasive, clinically relevant alternative to monitoring in blood.

BACKGROUND: Monitoring of psoralen concentration and time-course in PUVA patients is vital for efficient PUVA therapy. Blood sampling is invasive and labour-intensive and thus unsuited for routine use and repeat measurements over the course of therapy. OBJECTIVE: Psoralen pharmacokinetics in saliva were investigated and validated as a noninvasive, simple and biologically relevant alternative to measurements in blood. METHODS: The time-course of psoralen concentration was measured in saliva and serum of volunteers and patients receiving PUVA or extracorporeal photopheresis therapy. The samples were analysed by high-performance liquid chromatography. Three commonly used oral psoralen preparations were tested: Psoraderm5 (5-methoxypsoralen; 5-MOP), Meladinine and Oxsoralen (both 8-methoxypsoralen; 8-MOP). RESULTS: The pharmacokinetic parameter Cmax in saliva averaged 10% (range 6-20%) of the serum values for 8-MOP, and < or = 4% for 5-MOP. These concentrations correspond to the therapeutically relevant, non-albumin-bound fraction of psoralen in serum that is available to diffuse into the tissues. The parameter tmax in saliva and serum coincided, indicating that psoralens diffuse rapidly between the two compartments. CONCLUSION: Monitoring of psoralens in saliva is a valuable, noninvasive alternative to measurements in serum, suitable for routine use. A series of five or six saliva samples is sufficient to determine tmax in a patient beginning photochemotherapy. To determine Cmax, three independent saliva measurements at t = tmax are recommended.

Plasma and buffy coat concentration of 8-methoxypsoralen in patients treated with extracorporeal photopheresis.

Recently, a new therapy involving an extracorporal activation of orally administered 8-methoxypsoralen (8-MOP), photosensitizing furocoumarin, is established for the treatment of different skin diseases, extracorporeal photopheresis (ECP). The pharmacokinetic profile of 8-MOP has been pursued as part of a clinical study which should assess the efficacy of ECP in patients with progressive systemic sclerosis and cutaneous T-cell lymphoma. The enormous intra-individual variations proofed for plasma as well as buffy coat concentration are unfavourable for oral 8-MOP therapy. Therefore, the introduction of liquid 8-MOP formulation that allows the direct administration of the drug in to the treatment bag of the ECP device is challenging.

[Balneophotochemotherapy of lichen ruber. Personal results and comparison with photochemotherapy modalities employed up to now]. / Balneophotochemotherapie des Lichen ruber. Eigene Ergebnisse und Vergleich mit bisher angewandten Photochemotherapiemodalitäten.

Twelve patients with extensive lichen planus, resistant to different regimes of prior external and internal therapy, were treated with PUVA-bath photochemotherapy (psoralen bath followed by UVA irradiation) using bath water containing 0.5 mg/L of 8-methoxypsoralen (8-MOP). In 11 of the 12 patients, the skin lesions showed a significant improvement or even complete remission within six weeks of treatment. In one patient, only limited clinical improvement could be achieved. A mean of 19.1 (SD +/- 3.6) PUVA-bath treatments were carried out. The mean cumulative UVA-dose given until clearance of the lichen planus was 16.7 (SD +/- 4.8) J/cm2. No side effects were seen except an increased phototoxic reaction in two patients manifested as slight erythema. The results of this trial show, that PUVA-bath photochemotherapy with 8-MOP is an effective therapeutic alternative to all other known therapies in the treatment of extensive, exanthematic and also hypertrophic-hyperkeratotic lichen planus. In comparison to oral PUVA therapy and PUVA-bath therapy using 4,s',8-trimethoxypsoralen, balneophotochemotherapy with 8-MOP shows an excellent efficiency-side effect correlation. The clearance of the refractive skin lesions by balneophotochemotherapy with 8-MOP demonstrates the superiority of this therapy over all other common therapeutic modalities used for lichen planus.

Spectrofluorimetric determination of 5-methoxypsoralen pharmacokinetic in patients' serum.

In medicine, psoriasis and vitiligo are most often treated with PUVA therapy (psoralen plus ultraviolet A). The determination of psoralen in patients' blood is necessary, as it is admitted that the therapeutic efficiency depends on drug concentration in patients' serum. The amount of UVA to administer is inversely proportional to serum peak concentration. High-performance liquid chromatography (HPLC) and gas chromatography are the most employed methods for determining psoralens in patients' serum. The 2 techniques are precise and very sensitive, but time consuming. The aim of this paper is to propose a suitable method which is rapid and simple. It is a spectrofluorimetric technique for 5-methoxypsoralen (5-MOP) determination in the serum of patients treated with PUVA therapy. 5-MOP extraction was carried out with an heptane/dichloromethane mixture (4/1; v/v), according to the Stolk method (1980). A calibration curve (CC) was plotted from 5-MOP concentrations (range 50, 100, 200, 300, 400, 500 ng/ml). The CC was linear with a good coefficient of correlation: r = 0.9971, and a suitable coefficient of variation (CV) of 7.0%. The recovery of the method ranged from 85.3 +/- 4.2 to 108 +/- 4.1%. The assay precision gave a CV ranging from 0.10 to 6.90%, with an error inferior to +/-10%. The method did not reveal any interference from serum components on the 5-MOP emission wavelength. The limit of detection of 5-MOP was 15 ng/ml. The proposed procedure was proved to be appropriate for a rapid determination of 5-MOP in patients' serum. This technique could also be employed for other psoralens used in PUVA therapy (e.g., 8-methoxypsoralen).