Conversion of FAD to FMN and riboflavin in plasma: effects of measuring method

The stability of flavin adenin dinucleotide (FAD) in plasma was studied under a low-intensity light and FAD was found to be converted to flavin mononucleotide (FMN) and riboflavin (RF) in both human and rat plasma. The hydrolysis rates of FAD in plasma at 4 degrees C were lower than those at 37 degrees C. In addition, the hydrolysis rates were markedly inhibited when EDTA, known as an anticoagulant, was added to plasma. These results indicated that plasma samples in pharmacokinetic studies should be pretreated with EDTA, extracted at the earliest convenience and lower temperature like 4 degrees C to keep a high stability. The pharmacokinetic study after intravenous administration of FAD at a dose of 500 nmol/kg as FAD in rats was performed with plasma samples after addition of EDTA under strict light and temperature control. A measurable amount of FAD in plasma together with rapid conversions of FAD to FMN and RF were observed in rat plasma. The AUC values (mean+/-S.D. of 4 rats) for FAD, FMN and RF were 707+/-378, 3643+/-958 and 30095+/-3544 nmol x min/l, respectively. Using excess EDTA under strict temperature and light control may be useful for assessment of vitamin B2 in the in vivo study.

Effects of pretreatment of needle puncture and sandpaper abrasion on the in vitro skin permeation of fluorescein isothiocyanate (FITC)-dextran

Microneedle systems have gained attention as having many advantages over transdermal patches and hypodermic needles. The procedure provides adequate skin permeation rates without pain or severe infection. To obtain information for designing a microneedle system, macroneedles were used instead of microneedles to investigate the effects of pretreatment of needle puncture in the skin barrier stratum corneum on in vitro skin permeation of fluorescein isothiocyanate (FITC)-dextrans (4.3, 9.6 and 42.0 kDa) (FD-4, FD-10 and FD-40). The effect of sandpaper abrasion was also investigated for comparison. Both pretreatments on the skin barrier significantly increased the skin permeation of FDs. Lactate dehydrogenase (LDH) leaching was measured after pretreatment of macroneedle and sandpaper abrasion on the skin to evaluate the skin damage by these pretreatment methods. Lower leaching of LDH was observed after macroneedle puncture than after sandpaper abrasion. Next, a parallel permeation-resistance model of the skin barrier was established. Skin permeation of FD-10 was predicted by the model as a function of the number of pores in the skin barrier. Our results suggest that needle puncture may provide a safe, efficient and controllable alternative for increasing transdermal drug delivery.

Analysis of in Vitro Skin Permeation of 22-Oxacalcitriol Having a Complicated Metabolic Pathway

PURPOSE

The purpose of this study is to analyze simultaneous skin permeation and metabolism of 22-oxacalcitriol (OCT) having several metabolites in skin by observing skin permeation of only unchanged OCT through excised rat skin.

METHODS

A diffusion model including metabolic processes was employed to express simultaneous skin permeation and metabolism of OCT. In vitro permeation experiments of OCT from Oxarol ointment through full-thickness and stripped rat skin were carried out using Franz-type diffusion cells. Time courses of unchanged OCT amounts in ointment, skin, and receptor fluid were determined and fitted to diffusion equations to obtain permeation parameters and a metabolic rate.

RESULTS

Fitting curves of the skin permeation profile obtained by the model were sufficiently close to observed data of unchanged OCT amounts in ointment, skin, and receptor fluid. The following parameters were obtained: metabolic rate of 1.37 x 10(-1) h(-1), and diffusion constants of OCT in stratum corneum (SC) (D(SC)) and viable epidermis and dermis (VED) (D(VED)) of 1.50 x 10(-7) and 2.96 x 10(-4) cm2/h, respectively. The partition coefficient of OCT for SC/ointment (K(SC/D)) was 7 times greater than that of VED/ointment (K(VED/D)).

CONCLUSIONS

The present analysis made it possible to calculate skin permeation parameters (partitioning, diffusivity, and metabolic rate) of OCT without requiring metabolic information, e.g., quantification of metabolites or identification of metabolic pathways. This would be widely applicable for drugs that are not suitable for conventional methods due to complicated metabolic pathways.

Kinetic Analysis on the Skin Disposition of Cytotoxicity as an Index of Skin Irritation Produced by Cetylpyridinium Chloride: Comparison of In Vitro Data using a Three-Dimensional Cultured Human Skin Model with In Vivo Results in Hairless Mice

PURPOSE

The aim of this study was to kinetically and dynamically analyze in vitro cytotoxicity as an index of skin irritation by use of a three-dimensional cultured human skin model and to compare the in vitro assay data with data from living animals.

METHODS

A cationic surfactant, cetylpyridinium chloride (CPC), was selected as a model irritant. Living skin equivalent-high (LSE-high) and hairless mice were used for the in vitro and in vivo tests, respectively. Skin irritation dermatodynamics was evaluated by calorimetric thiazoyl blue (MTT) conversion assay both for in vitro and in vivo tests, whereas dermatokinetics of CPC in LSE-high and mouse skin were evaluated using HPLC.

RESULTS

The time course of cell viability in the skin after application of CPC to intact skin was distinctly different from that of stratum-corneum-stripped skin in both LSE-high and hairless mice. Biphasic behavior characterized by two first-order rates with an inflection time point was observed in intact skin, whereas cell viability monoexponentially decreased immediately after CPC application in stripped skin. The time courses of cell viability in the skin and dermatodynamics were closely related to that of dermatokinetics of CPC.

CONCLUSION

The present study demonstrates that the in vitro cytotoxic profile was similar to the in vivo cytotoxicity test and that dermatodynamics was related to dermatokinetics of CPC.

Enhancement of skin permeation of ketotifen by supersaturation generated by amorphous form of the drug

Pressure sensitive adhesive (PSA) matrices containing amorphous ketotifen were prepared and evaluated for enhanced skin permeability of the drug. A solvent casting method using silicone-typed PSA was employed, and n-hexane, an original solvent for the PSA and one more solvent, dichloromethane, tetrahydrofuran, acetone, ethyl acetate or toluene, were used for complete dissolution of ketotifen and high dispersion in an amorphous state of the drug. Presence of the amorphous form was judged based on the in vitro drug release rate from the matrix. As a result, dichloromethane and tetrahudrofuran were selected as appropriate dilution solvents. In vitro permeation experiments through excised hairless mouse skin revealed that the steady-state flux from the amorphous ketotifen-dispersed matrices was about five times greater than that of the crystalline ketotifen-dispersed matrices, and that the enhancement ratio was in good agreement with the solubility ratio of the amorphous to crystalline form of the drug. Comparison of the skin permeation profiles of amorphous ketotifen-dispersed matrices between two different drug contents suggested that the steady-state flux was not influenced by the drug content. In addition, at both drug contents, the period of the steady-state permeation coincided with the time until the amorphous drug was depleted from the matrix. These results suggest that the increase in skin permeation of ketotifen from PSA matrix was due to the supersaturation generated by amorphous form, and that the amorphous form was stable during the application period.

Cultured skin loaded with tetracycline HCl and chloramphenicol as dermal delivery system: Mathematical evaluation of the cultured skin containing antibiotics

Dermal patches consisting of cultured human skin with antibiotics, which have a protective effect on wound skin as well as a preventative effect on second infection of the skin, were prepared and mathematically analyzed as a new drug delivery system (DDS) that can be applied to serious skin defects such as severe burns. In the present study, a three-dimensional cultured human skin model (living skin equivalent-high, LSE-high) was used as a cultured skin membrane and tetracycline HCl (TC-HCl) and chloramphenicol (CP) were used as antibiotics. At first, antibiotics were entrapped in the LSE-high from the dermal side through culture medium in order to obtain a drug-loaded LSE-high. The antibiotic release from the drug-loaded LSE-high was then examined and the resulting release data were used to calculate the effective diffusion coefficient of the antibiotics (D(LSE)) and initial loading concentration of the antibiotics (C0) in the LSE-high. The release profile of TC-HCl was represented by general diffusion-limited kinetics, whereas an initial burst effect was found in the release profile of CP. Therefore, the burst effect was taken into account for analyzing the release profile of CP. Stripped skin excised from hairless rats was used as a wound model, and the antibiotic permeation through the skin from aqueous solution was examined and evaluated using differential equations for Fick's second law of diffusion to obtain the effective diffusion coefficient of the antibiotics in the wound skin (D(skin)). Furthermore, the antibiotic permeation profile through the excised stripped skin from the drug-loaded LSE-high was measured and theoretically evaluated by Fick's second law of diffusion with previously obtained parameters (C0, D(LSE), D(skin)) using a newly constructed two- or three-layered diffusion model. The calculated concentrations of TC-HCl and CP in the upper epidermis of the model wound skin were over their minimum inhibitory concentration (MIC) for several hours against various bacteria, suggesting that this dosage system is useful for the treatment of severe burns. In addition, the present analytical method and diffusion model, with the drug-loaded LSE-high and stripped rat skin, are useful tools for evaluating this new DDS.

Effect of electroporation on the electroosmosis across hairless mouse skin in vitro

The effect of electroporation on the iontophoresis-produced electroosmosis across the skin was evaluated by measuring the permeability of hairless mouse skin, to mannitol, a non-electrolyte, in vitro. Immediately after electroporation by squared pulses (10 times/s) at 100, 150 or 200 V for 1 ms, anodal iontophoretic permeations were determined at 0.4 mA/cm2 for 4 h. The observed iontophoretic permeability of mannitol was higher with electroporation pretreatment than without pretreatment. The enhanced flux of mannitol induced by electroporation, however, was due to increased passive diffusion. The contribution of convective or osmotic flow caused by anodal iontophoresis on skin permeation of mannitol was decreased by the pretreatment. In addition, osmotic flow was decreased with an increase in the applied voltage for electroporation. In contrast, mannitol flux during cathodal iontophoresis at 0.4 mA/cm2 after 150 or 200 V electroporation was higher than without electroporation as well as anodal iontophoresis, but cathodal iontophoretic flux after electroporation was lower than without iontophoresis. The neutral high-molecular compound dextran rhodamine B was also used as a second model. Anodal iontophoresis alone did not increase skin permeability of the compound. However, electroporation pretreatment before anodal iontophoresis enhanced the skin permeation of dextran rhodamine B, which was due to increased osmotic flow induced by this combination. These results suggest that electroporation decreases the electroosmosis produced by iontophoresis, and that electroporation increases skin permeability to neutral low and high model compounds (mannitol and dextran rhodamine B) probably due to an enlarged permeation pathway. Thus, electroporation affects osmotic flow from the anode to cathode during iontophoresis. Therefore, one has to pay attention to the change in electroosmosis produced by iontophoresis for the combined use of electroporation and iontophoresis to attain a high skin-penetration enhancing effect.

Usefulness of coadministration of bucolome in warfarin therapy: pharmacokinetic and pharmacodynamic analysis using outpatient prescriptions

Bucolome, a nonsteroidal anti-inflammatory drug, has often been coadministered to patients who take warfarin as an anticoagulant. This combination increases the anticoagulant effect, which is most likely due to the interaction of bucolome with the pharmacokinetics (PK) or pharmacodynamics (PD) of warfarin. More than 30 years ago the mechanism of this interaction was reported to be inhibition of warfarin protein binding by bucolome, and the inhibition of warfarin metabolism by bucolome was also recently reported. Here, we examined daily doses of warfarin and its anticoagulant effect (thrombo-test, TT) in outpatient prescriptions in five hospitals to elucidate the drug interaction and the usefulness of this drug combination. Among the warfarin prescriptions, 78 were for patients also taking bucolome and 99 were for patients not taking bucolome. The daily dose of warfarin in patients taking bucolome was significantly lower than those without bucolome (ca. 40%). TT in patients taking bucolome was significantly lower as compared to those not taking bucolome. Control of the anticoagulant effect was greater with coadministration of bucolome and warfarin than with warfarin alone. PK and PD analysis of our results suggests that the improved therapeutic effect resulting from coadministration of warfarin with bucolome was due to lower and less patient-to-patient variation of intrinsic hepatic clearance (CL(int)) of warfarin, since bucolome decreased the high CL(int) but did not have a great effect on the low CL(int). In conclusion, administration of bucolome in warfarin therapy is useful to control the anticoagulant effect of warfarin. Attention should also be paid to the enzymatic inhibition by bucolome on the PK of coadministered drugs.

Utility of a three-dimensional cultured human skin model as a tool to evaluate the simultaneous diffusion and metabolism of ethyl nicotinate in skin

The simultaneous diffusion and metabolism of ethyl nicotinate (EN) in a cultured human skin model, Living Skin Equivalent-high, was evaluated by the in vitro skin permeation and metabolism experiments, and esterase distribution was also determined. Theoretical calculations using Fick's 2nd Law of Diffusion with Michaelis-Menten kinetics were performed to obtain the permeation and metabolic parameters together with information on enzyme distribution. The obtained data was compared with the corresponding results in excised hairless rat skin. The partition coefficient of EN from the vehicle to the skin was of the same order of magnitude for the cultured human skin and hairless rat skin, but the diffusion and metabolic parameters were different. Esterase concentration in the epidermal membrane was greater than in the dermis of cultured skin, which was similar to hairless rat skin. Taking into account the similarities and differences between the membranes, the cultured human skin model can be utilized as a model membrane to rapidly predict simultaneous diffusion and metabolism of the prodrug through human skin.

Decrease in Skin Permeation and Antibacterial Effect of Parabens by a Polymeric Additive, Poly(2-methacryloyloxyethyl phosphorylcholine-co-butylmetacrylate)

The inhibitory effect of poly(2-methacryloyloxyethyl phosphorylcholine-co-butylmetacrylate) (PMB) on the in vitro skin permeation of p-hydroxybenzoic acid and its esters (parabens; methylparaben, ethylparaben, n-propylparaben and n-butylparaben) as model compounds was evaluated. Solubility of the parabens in distilled water was increased by addition of PMB, and the increasing ratio was dependent on the concentration of PMB. The increment of the ratio was more marked in lipophilic parabens than hydrophilic ones. Skin permeability of parabens from their aqueous suspensions was decreased by addition of PMB, and the decreasing ratio was dependent on the PMB concentration. Then, antibacterial effect of parabens of their aqueous solutions was determined with and without PMB by measuring minimum inhibitory concentration (MIC) against E. coli and S. aureus. As results, MIC and antibacterial effect were increased and decreased, respectively, by addition of PMB. The contribution of PMB was more marked in butylparaben than methylparaben. These decreases in skin permeation and antibacterial effect of parabens by PMB are probably due to a higher solubility in water and a lower partition to the skin and bacterial membranes of parabens by addition of PMB.

The synergic effects of various electrolytes and electroporation on the in vitro skin permeation of calcein

Various electrolytes in test solutions applied to the skin were evaluated with regard to their effects on enhanced skin permeation of calcein as a model permeant by electroporation (EP), which is a physical means to increase skin penetration by applying a high voltage pulse on the skin surface. Calcein solution (1.0 mM) containing different electrolytes at a concentration of 150 mM was applied to excised hairless rat skin, and a 10-ms electric pulse of 300 V was applied to the skin surface ten times (one pulse every second) at the beginning of the in vitro permeation experiments. The following results were obtained: (i) addition of several electrolytes, such as CaCl2 and NaCl, further increased the EP-enhanced skin permeation of calcein when compared to treatment without these electrolytes; (ii) Ca2+ and Mg2+ exerted a greater effect than other cations (Na+, Zn2+, Cu2+, Fe3+ and Al3+); (iii) with simultaneous application of CaCl2 and EP, the effect of anodal EP was much greater than that of cathodal EP; (iv) the penetration-enhancing effects of CaCl2 were also obtained with EP pretreatment followed by calcein addition; and (v) skin permeation was greatly increased particularly with simultaneous application of EP and Ca2+. These substantial combined synergic effects of EP and electrolytes, particularly those containing CaCl2, MgCl2 and CaBr2, may be related to the disruptive and retrievable functions of the biggest barrier of skin, the stratum corneum, of these electrolytes.

In vitro permeation of several drugs through the human nail plate: relationship between physicochemical properties and nail permeability of drugs

The objectives of the present study are to clarify the relationship between the physicochemical properties and the nail permeability of drugs through human nail plates. Homologous p-hydroxybenzoic acid esters were used to investigate the relationship between the octanol/water partition coefficient and the permeability coefficient of several drugs. The nail permeability was found to be independent of the lipophilicity of a penetrating drug. However, the nail permeability of several model drugs was found to markedly decrease as their molecular weights increased. The nail permeability of an ionic drug was found to be significantly lower than that of a non-ionic drug, and the nail permeability of these drugs markedly decreased as their molecular weights increased. The permeation of a model drug, 5-fluorouracil (5-FU), through healthy nail plates was also determined and compared with that through nail plates with fungal infections. The drug permeation through a nail plate decreased with an increase in nail plate thickness. Nail plates with fungal infections exhibited approximately the same 5-FU permeation as healthy nail plates. We suggest that the permeability of a drug is mainly influenced by its molecular weight and permeability through nails with fungal infection can be estimated from data on healthy nail permeability.

Mechanism of the synergic effects of calcium chloride and electroporation on the in vitro enhanced skin permeation of drugs

We have already reported the substantial synergic effects of CaCl(2) and electroporation (EP) on in vitro skin permeation of calcein and FITC dextrans. In the present paper, we investigated the mechanisms for these effects by considering changes in lamellar structure and barrier recovery time of the biggest skin barrier, the stratum corneum, by this combined treatment. The change in skin lamellar structure was evaluated by lipid mobility in the stratum corneum using ATR-FTIR, calcein release from stratum corneum-lipid liposomes (SCLL), in vitro skin permeation of calcein and transepidermal water loss (TEWL). The ATR-FTIR measurement, in vitro skin permeation and changes in TEWL were also used for examining the barrier recovery time. The C-H stretching band of skin lipids produced with EP was blue-shifted when compared to that without EP. Asymmetric C-H stretching was highest with EP in CaCl(2) solution. Little release of calcein was observed from SCLL without EP, whereas higher releases were observed after EP with or without NaCl or CaCl(2). Particularly high calcein release (>20%) was observed over 60 min with EP in CaCl(2) solution. The in vitro permeation study of calcein was conducted through excised hairless rat skin that was pretreated with EP before skin excision. Permeation rate was highest in skin excised immediately after in vivo EP, and this rate decreased with time after EP treatment. TEWL recovered to control levels within 2 h after EP in distilled water or NaCl solution, whereas high TEWL was maintained after EP in CaCl(2) solution. These results suggest that at least lamellar destruction of stratum corneum must be related to the enhanced skin permeation of drugs by the combination of CaCl(2) and EPF. On the other hand, a prolonged enhancing effect on the skin permeation of calcein by this combination may be due to a high lamellar destruction and/or delayed barrier repair of stratum corneum.

Effect of electric field on the enhanced skin permeation of drugs by electroporation

Electroporation (voltage; 200 V) was applied using an exponentially decaying electric pulse generator on hairless rat skin using different shapes of electrodes, and the in vitro skin permeation of benzoate was measured as an index of the effectiveness of electroporation. Despite the same voltage of application, the skin permeation of benzoate was markedly different by the electrode shapes. Several experiments hereafter suggest that this reason was probably due to different 2-dimensional electric fields in the skin barrier, stratum corneum, and the voltage decreasing pattern applied. To confirm whether this phenomenon was specific for benzoate, diclofenac having a similar pKa was selected to carry out the same kind of examination. As a result, the skin permeability of diclofenac was influenced by 2-dimensional electric fields in the stratum corneum and the voltage decreasing pattern, similar to the benzoate permeation. Next, a rectangular pulse generator, where no decaying pattern was obtained for the application voltage, was used to measure the effect of electroporation on the skin permeation of diclofenac. As expected, the enhanced skin permeation of diclofenac was dependent only on the electric field when using the rectangular pulse generator. These results suggest that the electric field and time profile of the voltage (or AUC of voltage against time) at electroporation are very important factors to increase the efficacy of electroporation, and that the efficacy can be optimized by the shape of electrodes in addition to the application conditions of electroporation.

Liquid chromatographic determination of unbound flecainide in therapeutic drug monitoring

An assay method was developed for determining unbound flecainide in serum by reversed phase-high performance liquid chromatography (HPLC). Serum water including unbound flecainide was separated by ultrafiltration of the serum sample and subjected to C(18)-cartridge extraction followed by HPLC analysis. The recovery of flecainide from serum water was greater than 93%. The coefficient variations for intra- and inter-day assay of flecainide were smaller than 2.4 and 3.7%, respectively. We applied the method to determining unbound flecainide in serum samples collected from 20 patients receiving oral flecainide (150-300 mg/day) for tachyarrhythmia. Total and unbound concentrations for serum flecainide were 403.5+/-200.8 ng/ml and 180.2+/-95.0 ng/ml, respectively. Linear relationship was observed between total and unbound concentrations (r=0.978, P<0.0001). Percent unbound (44.3+/-5.7%) determined in the present study agreed with the reported values. The percentage unbound tended to increase in the samples with lower alpha(1)-acid glycoprotein (<60 mg/dl). The assay method can be applied to routine determination of unbound flecainide in therapeutic drug monitoring.

Design and feasibility assessment of topically applied drug formulations for electroporation

Few studies have been reported on the design of topical formulations consisting of electrodes and active drugs for electroporation as a means to increase skin permeability of the drugs, although many studies were reported for the effect of this physical means using aqueous drug solutions. We, therefore, designed a prototypic reservoir and matrix topical formulations that are suitable for electroporation in the present study. Plate-plate Ag electrodes and sodium diclofenac were used as model electrodes and the drug, respectively. The in vitro skin permeations of the drug obtained from the reservoir and matrix formulations were slightly higher than that from an aqueous suspension. This may be due to slightly higher electric field in the skin barrier for the presently designed formulations than that for the aqueous suspension. The present feasibility test suggests that these reservoirs and matrix formulations are useful prototypic topical formulations for electroporation application to improve the drug permeability through skin.

The Effects of Calcium Chloride and Sodium Chloride on the Electroporation-Mediated Skin Permeation of Fluorescein Isothiocyanate (FITC)-Dextrans in Vitro

We previously reported the substantial synergic effects of electroporation and electrolytes, particularly those containing CaCl(2) on the skin permeation of the model low-molecular weight compound, calcein. We then investigated the effects of electroporation (300 V, 10 msx10 times) and 150 mM NaCl or CaCl(2) on skin permeation of higher molecular weight compounds, fluorescein isothiocyanate (FITC)-dextrans (FD-4, FD-10 and FD-40; average molecular weight, 4.4, 9.6 and 35.6 kDa, respectively) using excised hairless rat skin. The observed steady state flux of FD-4 was 1.3 pmol/cm(2)/h after electroporation without NaCl or CaCl(2). The flux did not differ greatly from that without electroporation. In contrast, a much higher steady state flux was observed after electroporation with NaCl or CaCl(2) (2.5 and 8.2 pmol/cm(2)/h, respectively). For FD-10 and FD-40, no flux was detected with electroporation in water (without electrolytes) or without electroporation. On the other hand, high skin permeation was observed after electroporation in NaCl or CaCl(2) solution (FD-10: 7.5 and 18.2 pmol/cm(2)/h, FD-40: 4.5 and 9.3 pmol/cm(2)/h in NaCl and CaCl(2), respectively). The effects of CaCl(2) on FD permeation were greater than those of NaCl. The present finding suggests that electroporation application in the presence of electrolytes, particularly CaCl(2), was very effective in increasing transdermal delivery of water-soluble macromolecules.

Kinetic analysis on the in vitro cytotoxicity using Living Skin Equivalent for ranking the toxic potential of dermal irritants

The extent of cytotoxicity injured by several skin irritants was kinetically measured and analyzed in a three-dimensional cultured human skin model, Living Skin Equivalent-002 (LSE). Colorimetric thiazoyl blue (MTT) conversion assay was selected as a cytotoxicity assay, and olive oil (OO), lactic acid (LA), Triton X-100 (TX) and sodium lauryl sulfate (SLS) were evaluated as model irritants. OO had almost no effect on the viability of LSE. When the other irritants were applied on the full-thickness LSE, two first-ordered decreasing phases, initial slow and following rapid phases, were found in the viability of LSE. LA and TX showed a bigger difference between the slow and rapid rates than SLS to show an inflection. The inflection time point from the slow to rapid rate was dependent on the kind and concentration of irritants applied. The higher the concentration of irritants applied, the more rapid the inflection point was observed. When LA and SLS were applied on the stratum corneum-stripped LSE, on the other hand, viability was mono-exponentially decreased with time. LA, TX and SLS probably decrease the barrier function of the stratum corneum to increase the rate of cytotoxicity during the irritant application. Interestingly, the rate of cytotoxicity on the stripped skin was similar to the late rapid rate on the full-thickness skin in LA not in SLS. These results suggest that cytotoxicity of skin irritants on the full-thickness LSE can be represented by two first-order kinetics, and that the skin irritation rate is closely related by the barrier function of skin as well as the application concentration and intrinsic toxicity of irritants.

[Fast-disintegration oral tablets having sustained release property]

Fast-disintegrating (FD) tablets containing nicorandil-loaded dry emulsions were prepared and their controlled-release properties were examined and compared with the plain FD tablets (FD tablets without dry emulsions) and commercial tablets. The dry emulsions were prepared with myristyl alcohol and stearyl alcohol and their property was modified by mixing the ratio of the two alcohols. Disintegration time of the prepared FD tablets was sufficiently fast (i.e., 12 to 23 s). In vitro release of nicorandil from the FD tablets containing the dry emulsions was sustained over 6 h, while that from plain FD and commercial tablets was complete within 5 min. In vivo absorption of nicorandil from the tablets was evaluated by oral administration in beagle dogs. FD tablets containing dry emulsions showed a similar AUC, lower Cmax, and delayed Tmax compared to the plain FD and commercial tablets. These results suggest that the dry emulsion-loaded FD tablets can be utilized to improve the sustained-release property of active drugs.

The enhancing effect of a triethanolamine-ethanol-isopropyl myristate mixed system on the skin permeation of acidic drugs

The effect of a TEI enhancer mixed system consisting of triethanolamine (T), ethanol (E) and isopropyl myristate (IPM) on the skin permeation of acidic, basic and neutral drugs were evaluated in vitro using excised hairless rat skin. The binary enhancer system consisting of IPM and ethanol (El) produced marked improvement on the penetration of all the drugs tested. When T was added to the EI system, a greater enhancing effect was found only on acidic drugs with a carboxyl group, compared with the flux in the EI system. On addition of another amine to the EI system, instead of T, mefenamic acid (MA), which exhibited the highest enhancing effect of the model drugs, showed an approximately 14-180 times greater flux than when delivered by the EI system. On simultaneous application of isosorbide dinitrate (ISDN) with MA in the TEI system, the flux of MA increased on increasing the T concentration in the TEI system, while, the flux of ISDN, a neutral drug, was unaffected by the T concentration. Application of MA in the EI system after pretreatment of the TEI system showed that the residual amount of T in the skin plays an important role in the skin permeation of MA. Furthermore, at a fixed concentration of MA, the flux of MA increased on increasing the T concentration in the TEI system, while the flux of E remained unchanged. Finally, the infrared spectrum of MA with amine in the E solution indicated that the carboxyl group of MA was ionized. These results demonstrated that the formation of an ion pair between MA and T, but not the effect of T on the skin, may be responsible for the enhanced skin permeation of MA using the TEI system.

Introduction of poly-L-lactic acid microspheres into the skin using supersonic flow: effects of helium gas pressure, particle size and microparticle dose on the amount introduced into hairless rat skin

A microparticulate bombardment system loaded with DNA- and RNA-coated gold and tungsten microparticles (diameter 1-3 microm; density about 19 g cm(-3)), the Helios gene gun system (Helios gun system), has been used to deliver a gene into cells by accelerating the microparticles to high velocity using a supersonic flow of helium gas. To investigate whether drug-loaded microspheres, > 20 microm in diameter and about 1.0 g cm(-3) in density, could be delivered in powder form quantitatively into the skin using the Helios gun system equipped with a cartridge container fitted with a rupture membrane, we investigated the effect of the helium gas pressure in accelerating indometacin-loaded poly-L-lactic acid (PLA) microspheres, as well as the particle size and the bombardment dose on delivery into the skin. Introduction of indometacin (i.e. indometacin-loaded PLA microspheres) after bombardment, with 3.0 mg indometacin-loaded PLA microspheres of a particle size of 20-38, 44-53 and 75-100 microm at a helium pressure of 100, 200 and 300 psi, of the abdomen of hairless rats increased in parallel with the helium pressure and it was also affected by the particle size, being highest at a diameter of 75-100 microm. However, introduction of higher amounts of PLA microspheres resulted in more severe skin erythema (skin damage) as monitored by the Draize score. Using lower bombardment doses (0.5 and 1.0 mg), the efficiency of introduction was improved and the skin damage markedly reduced. Moreover, discrete bombardment with a low dose provided a more efficient introduction of indometacin and less skin damage. These results suggest that bombardment injection of drug-loaded microspheres in a powdered form by the Helios gun system appears to be a very useful tool for the quantitative delivery of a variety of drugs and an alternative to parenteral injection by needle, especially for delivering water-soluble macromolecules.

Effects of particle size, helium gas pressure and microparticle dose on the plasma concentration of indomethacin after bombardment of indomethacin-loaded poly-L-lactic acid microspheres using a Helios gun system

We investigated the effects of the particle size of indomethacin-loaded poly-L-lactic acid microspheres (IDM-loaded PLA MS), the helium pressure used to accelerate the particles, and the bombardment dose of PLA MS on the plasma concentration of IDM after bombarding with IDM-loaded PLA MS of different particle size ranges, 20-38, 44-53 and 75-100 microm, the abdomen of hairless rats using the Helios gene gun system (Helios gun system). Using larger particles and a higher helium pressure, produced an increase in the plasma IDM concentration and the area under the plasma concentration-time curve (AUC) and resultant F (relative bioavailability with respect to intracutaneous injection) of IDM increased by an amount depending on the particle size and helium pressure. Although a reduction in the bombardment dose led to a decrease in C(max) and AUC, F increased on decreasing the bombardment dose. In addition, a more efficient F was obtained after bombarding with IDM-loaded PLA MS of 75-100 microm in diameter at each low dose in different sites of the abdomen compared with that after bolus bombardment with a high dose (dose equivalent). These results suggest that the bombardment injection of drug-loaded microspheres by the Helios gun system is a very useful tool for delivering a variety of drugs in powder form into the skin and systemic circulation.

Utility of MTT assay in three-dimensional cultured human skin model as an alternative for draize skin irritation test: approach using diffusion law of irritant in skin and toxicokinetics-toxicodynamics correlation

PURPOSE

A cytotoxicity assay using a three-dimensional cultured human skin model, Living Skin Equivalent-high (LSE-high) was evaluated as an alternative to the Draize skin irritation tests using animals. A relation between the cytotoxicity and calculated concentration of an irritant in skin was also evaluated.

METHODS

Colorimetric thiazoyl blue (MTT) conversion assay and a surfactant, cetylpyridinium chloride (CPC), were selected as a cytotoxicity assay and a model irritant. The fraction of dead cell number in the MTT assay or the Draize irritation score (in vitro and in vivo irritation data, respectively) was treated as a function of CPC concentration in the viable skin of LSE-high and guinea pig. Separately, in vitro permeations of CPC through the LSE-high or excised guinea pig skin were determined to calculate the average concentration of CPC in the viable skin using the Fickian diffusion theory. The obtained relations between the irritation scores and CPC concentration were evaluated by the Emax model (Hill equation).

RESULTS

CPC concentration showing 50% irritation (IC50) was similar for the MTT assay (18.9%) and Draize test (12.3%), and a good relationship (r = 0.981) was observed between the fraction of dead cell number and the Draize score. In contrast, IC50, 1.32%, for the MTT assay in LSE-high was much lower than that using guinea pig skin. We then corrected the results for the MTT assay using a ratio of IC50 in guinea pig skin against LSE-high, resulting in a good relation between both MTT results in guinea pig skin and LSE-high.

CONCLUSION

The present results suggest that the MTT assay using LSE-high may be utilized as an alternative for the Draize test in animals for evaluating skin irritation.

Targeting of salicylate to skin and muscle following topical injections in rats

The process of systemic absorption and tissue targeting efficacy of salicylate (SA) following intracutaneous (i.c.), subcutaneous (s.c.) and intramuscular (i.m.) injections of its sodium salt in rats were evaluated by determining the drug concentration at the injection site and surrounding tissues. After i.c. and s.c. injections, SA was absorbed into the systemic circulation from the muscular vessels as well as the cutaneous or subcutaneous vessels beneath the injection site, and the AUC of the drug in the muscle was extremely high. Following i.m. injection, SA was rapidly absorbed into the systemic circulation mostly from the muscular vein. These results suggested that i.c. and s.c. injections have high degrees of targeting efficacy to the muscle, whereas i.m. injection is not appropriate for drug retention in muscle. In contrast, most of the topically applied drug was absorbed from the cutaneous vessels, and little drug migration to the muscle was observed. Thus, the skin pharmacokinetics of SA after i.c. injection was also markedly different from those after topical application on the skin. These results suggested that the i.c. and s.c. injections may be a good means to improve the targeting ability of drugs to the muscle as well as the skin.

In vitro skin permeation of morphine hydrochloride during the finite application of penetration-enhancing system containing water, ethanol and l-menthol

The effects of composition of applied solutions, containing water, ethanol (EtOH) and l-menthol (LM) as penetration enhancers, on the in vitro permeation of morphine hydrochloride (MPH) through excised hairless rat skin were examined in finite application experiments. Three of the five different applied solutions contained almost saturated LM and two contained levels of LM below the limit of solubility. Despite similar pseudo steady-state fluxes (maximum fluxes observed) of MPH from the solutions, lag time for the permeation of MPH from the saturated systems was shorter than that from the unsaturated systems. Lag times for the permeation of EtOH and LM from the saturated systems were also shorter than those from the unsaturated systems. Thermodynamic activity of LM is important for the enhancing effect against MPH permeation. At the beginning for the permeation experiment, the activity of LM in the unsaturated systems was lower than that in the saturated solutions. As the skin permeability of EtOH was higher than that of other components, the content of EtOH in the applied solution gradually decreased with time, while the activity of LM increased eventually showing a sufficient enhancing effect. Solvent drag effect was not important for the permeation of MPH, since penetration rate of MPH was independent of the time course of that of EtOH. The amount of LM migrating into skin appeared to be the most important parameter for the penetration-enhancing effect of the mixed system in the in vitro permeation of MPH through excised hairless rat skin.