Eight-channel transceiver RF coil array tailored for ¹H/¹⁹F MR of the human knee and fluorinated drugs at 7.0 T

The purpose of this study was to evaluate the feasibility of an eight-channel dual-tuned transceiver surface RF coil array for combined (1)H/(19)F MR of the human knee at 7.0 T following application of (19)F-containing drugs. The (1)H/(19)F RF coil array includes a posterior module with two (1)H loop elements and two anterior modules, each consisting of one (1)H and two (19)F elements. The decoupling of neighbor elements is achieved by a shared capacitor. Electromagnetic field simulations were performed to afford uniform transmission fields and to be in accordance with RF safety guidelines. Localized (19)F MRS was conducted with 47 and 101 mmol/L of flufenamic acid (FA) – a (19)F-containing non-steroidal anti-inflammatory drug – to determine T1 and T2 and to study the (19)F signal-to-dose relationship. The suitability of the proposed approach for (1)H/(19)F MR was examined in healthy subjects. Reflection coefficients of each channel were less than -17 dB and coupling between channels was less than -11 dB. Q(L)/Q(U) was less than 0.5 for all elements. MRS results demonstrated signal stability with 1% variation. T1 and T2 relaxation times changed with concentration of FA: T1 /T2 = 673/31 ms at 101 mmol/L and T1 /T2 = 616/26 ms at 47 mmol/L. A uniform signal and contrast across the patella could be observed in proton imaging. The sensitivity of the RF coil enabled localization of FA ointment administrated to the knee with an in-plane spatial resolution of (1.5 × 1.5) mm(2) achieved in a total scan time of approximately three minutes, which is well suited for translational human studies. This study shows the feasibility of combined (1)H/(19)F MRI of the knee at 7.0 T and proposes T1 and T2 mapping methods for quantifying fluorinated drugs in vivo. Further technological developments are necessary to promote real-time bioavailability studies and quantification of (19)F-containing medicinal compounds in vivo.

Determination of Degradation Pathways and Kinetics of Acyl Glucuronides by NMR Spectroscopy

Acyl glucuronides have been implicated in the toxicity of many xenobiotics and marketed drugs. These toxicities are hypothesized to be a consequence of covalent binding of the reactive forms of the acyl glucuronide to proteins. Reactive intermediates of the acyl glucuronide arise from the migration of the aglycone leading to other positional and stereoisomers under physiological conditions. In order to screen for the potential liabilities of these metabolites during the early phase of pharmaceutical development, an NMR method based on the disappearance of the anomeric resonance of the O-1-acyl glucuronide was used to monitor the degradation kinetics of 11 structurally diverse acyl glucuronides, including those produced from the known nonsteroidal anti-inflammatory drugs (NSAIDs). The acyl glucuronides were either chemically synthesized or were isolated from biological matrices (bile, urine, and liver microsomal extracts). The half-lives attained utilizing this method were found to be comparable to those reported in the literature. NMR analysis also enabled the delineation of the two possible pathways of degradation: acyl migration and hydrolytic cleavage. The previously characterized 1H resonances of acyl migrated products are quite distinguishable from those that arise from hydrolysis. The NMR method described here could be used to rank order acyl glucuronide forming discovery compounds based on the potential reactivity of the conjugates and their routes of decomposition under physiological conditions. Furthermore, we have shown that in vitro systems such as liver microsomal preparations can be used to generate sufficient quantities of acyl glucuronides from early discovery compounds for NMR characterization. This is particularly important, as we often have limited supply of early discovery compounds to conduct in vivo studies to generate sufficient quantities of acyl glucuronides for further characterization.

In-silico model of skin penetration based on experimentally determined input parameters. Part I: experimental determination of partition and diffusion coefficients

Mathematical modeling of skin transport is considered a valuable alternative of in-vitro and in-vivo investigations especially considering ethical and economical questions. Mechanistic diffusion models describe skin transport by solving Fick's 2nd law of diffusion in time and space; however models relying entirely on a consistent experimental data set are missing. For a two-dimensional model membrane consisting of a biphasic stratum corneum (SC) and a homogeneous epidermal/dermal compartment (DSL) methods are presented to determine all relevant input parameters. The data were generated for flufenamic acid (M(W) 281.24g/mol; logK(Oct/H2O) 4.8; pK(a) 3.9) and caffeine (M(W) 194.2g/mol; logK(Oct/H2O) -0.083; pK(a) 1.39) using female abdominal skin. K(lip/don) (lipid-donor partition coefficient) was determined in equilibration experiments with human SC lipids. K(cor/lip) (corneocyte-lipid) and K(DSL/lip) (DSL-lipid) were derived from easily available experimental data, i.e. K(SC/don) (SC-donor), K(lip/don) and K(SC/DSL) (SC-DSL) considering realistic volume fractions of the lipid and corneocyte phases. Lipid and DSL diffusion coefficients D(lip) and D(DSL) were calculated based on steady state flux. The corneocyte diffusion coefficient D(cor) is not accessible experimentally and needs to be estimated by simulation. Based on these results time-dependent stratum corneum concentration-depth profiles were simulated and compared to experimental profiles in an accompanying study.

Effect of selected fluorinated drugs in a “ringing” gel on rheological behaviour and skin permeation

The purpose of the present study was to investigate the influence of different drugs exhibiting different solubility on the viscoelastic properties and on the skin diffusion profile of a ringing gel. In a preliminary rheology study with the placebo gel predominating elastic properties were confirmed and a temperature influence was indicated. Fluconazole, fludrocortisone-acetate, flumethasone-pivalate, flutamide and flufenamic-acid each 1% (w/w) were incorporated into the preparation and oscillatory measurements were performed at temperatures of 25, 28, 32 and 37 degrees C. In all drug containing formulations a high elastic G' value predominated the viscous G'' value. The highest G' value could be obtained with the incorporated flumethasone-pivalate. Additionally in almost all cases the G' values decreased with increasing temperature compared to the placebo gel. Additionally in vitro standard diffusion experiments using Franz-type cells and porcine skin were performed. Following rank order of the cumulative drug release after 48 h was obtained: fluconazole>flufenamic-acid>flumethasone-pivalate>flutamide>fludrocortisone-acetate. Furthermore an excellent chemical stability of all incorporated drugs was confirmed over 10 weeks.

Influence of Nanoencapsulation on Human Skin Transport of Flufenamic Acid

The effect of the inclusion of flufenamic acid in poly(lactide-co-glycolide) nanoparticles on the transport of flufenamic acid into excised human skin was investigated. Penetration and permeation data were acquired using two different in vitro test systems: the Saarbrucken penetration model, where the skin acts as its own receptor medium, and the Franz diffusion cell, where the receptor medium is a buffer solution. For the stratum corneum, no differences were found between nanoencapsulated and free drug. Drug accumulation in the deeper skin layers and drug transport across human epidermis were slightly delayed for the nanoencapsulated drug compared to the free drug after shorter incubation times (<12 h). In contrast, after longer incubation times (>12 h), the nanoencapsulated drug showed a statistically significantly enhanced transport and accumulation (p < 0.05). Additionally, nanoencapsulated flufenamic acid was visualized by multiphoton fluorescence microscopy. Particles were found homogeneously distributed on the skin surface and within the dermatoglyphs, but no nanoparticles were detected within or between the corneocytes.

Effects of various vehicles on the penetration of flufenamic acid into human skin

The effect of various vehicles (polyacrylate gels and wool alcohol ointments) on the penetration of flufenamic acid into excised human skin was investigated. Physico-chemical properties of the formulations were examined and discussed. Penetration data was gathered using two different in vitro test systems: the Saarbruecken penetration model (SB-M) and the Franz diffusion cell (FD-C). With wool alcohol ointments, drug concentration in the formulation was the decisive parameter for drug liberation and penetration. The incorporation of water into wool alcohol ointment led to increased drug amounts within the deeper skin layers (DSL), especially after longer incubation times. The drug concentration within the stratum corneum (SC) was not influenced by the bleeding effect of lipophilic, liquid components of the various wool alcohol ointments. With polyacrylate gels different results for liberation and penetration were observed. These results could be related to the effects of the drug concentration within the formulation and the penetration enhancers incorporated into the gels. Especially the effects of penetration enhancers clearly illustrated that liberation experiments do not predict the situation in the skin, but make experiments with a biological barrier essential. The high water content of the gels led to hydration of the skin specimen for the SB-M and the FD-C and therefore, in contrast to previous findings, comparable data were obtained in the penetration studies with both models. Furthermore, the quasi steady-state drug amount in the SC could be calculated for all formulations using an equation derived from a Michaelis-Menten kinetics. The data from both test systems were linearly correlated to each other. In addition, a direct linear relationship between the SC drug amount and the drug amount in the DSL was found as long as the quasi steady-state drug amount in the SC was not reached. A combination of all results might offer the chance to reduce the costs and to simplify the development of a new drug formulation.

Correlation between stratum corneum/water-partition coefficient and amounts of flufenamic acid penetrated into the stratum corneum

The stratum corneum of various donors differs in particular in the composition of the lipoidal phase. Considering the drug amounts penetrating into the stratum corneum a simple methodology to correlate these differences in the stratum corneum composition with the drug amounts detectable within the stratum corneum is desirable. Penetration experiments investigating several incubation times were carried out with three different skin flaps using the Saarbruecken penetration model and the lipophilic model drug flufenamic acid. The drug amounts within the stratum corneum were obtained with the tape-stripping technique, while the drug amounts present in the deeper skin layers were achieved by cryosectioning. The stratum corneum/water-partition coefficient was determined with the same three skin flaps to characterize the lipoidal stratum corneum phase in general, and the differences were attributed to the different amounts of ceramides and sterols. In addition, for the lipophilic drug flufenamic acid, a direct linear correlation was found between the stratum corneum/water-partition coefficients and the drug amounts penetrated into the stratum corneum for all investigated time intervals (correlation coefficients of r(30 min) = 0.998, r(60 min) = 0.998 and r(180 min) = 0.987). In contrast to the stratum corneum/water-partition coefficients, the determination of a corresponding relationship for the stratum corneum and the deeper skin layers failed due to the reason that steady-state conditions could not be achieved for the deeper skin layers during the investigated time intervals. In summary, the stratum corneum/water-partition coefficients offer the possibility to predict drug amounts within the stratum corneum of different donor skin flaps without a time consuming determination of the lipid composition of the stratum corneum.

Human skin penetration of flufenamic acid: in vivo/in vitro correlation (deeper skin layers) for skin samples from the same subject

Previously, the interest in in vivo/in vitro correlations in the dermal field of research has increased steadily. Unfortunately, in most cases the skin from different human donors was taken for in vivo and in vitro experiments, which led to problems concerning the interindividual variability of the skin. Therefore, we established a methodology to utilize the same skin for both sets of data. In time dependency, drug amounts in the stratum corneum and the deeper skin layers were determined from eight donors using the same skin area for in vivo and the corresponding in vitro tests. Penetration experiments were carried out with the lipophilic drug flufenamic acid dissolved in wool alcohols ointment as the model formulation, which was administered to the skin under "infinite dose" conditions. At different time points prior to starting the surgery, the drug preparation was applied topically on the edges of the skin area, which was planned for excision using Finn chambers. After anesthetizing the patient and disinfecting the operation area, the incubated skin pieces were cut off first and immediately frozen to limit further drug diffusion. In vitro experiments were performed on the remaining skin flap, using two different test systems, a penetration and a permeation model. At the end of all experiments (in vivo and in vitro) the skin specimens were segmented horizontally and the drug was extracted and quantified. The in vivo and in vitro drug amounts in the stratum corneum and the deeper skin layers, respectively, were compared. The inevitable use of unknown volumes of disinfectant in vivo (medical reasons) might be the reason why a correlation failed for the stratum corneum. Nevertheless, for both in vitro test systems a direct linear correlation was found for the deeper skin layers, which showed slopes of a = 3.2272 +/- 0.3933 (penetration model vs in vivo) and a = 1.7776 +/- 0. 1926 (permeation model vs in vivo). This difference demonstrates the varying influence of the test systems and represents a factor about which in vivo and in vitro data are shifted against each other. As far as the model drug flufenamic acid is concerned, this methodology represents a tool to predict drug penetration into the deeper skin layers in vivo after carrying out corresponding in vitro experiments. Therefore, the potential is given to reduce the number of in vivo experiments, the risk for the volunteers, and the costs for the development of new drug preparations.

Etofenamate levels in human serum and synovial fluid following iontophoresis

The absorption of etofenamate (CAS 30544-47-9, Rheumon gel) by iontophoresis in 11 patients with low back pain and in 13 patients with synovitis of the knee was evaluated. During the 5-day treatment period, the test gel in a quantity corresponding to 100 mg etofenamate was applied to affected body regions every day by 20-min iontophoresis sessions. Two hours after the fifth application, the concentration of etofenamate in serum and synovial fluid (in patients who had knee joint iontophoresis) were measured by HPLC. Iontophoresis of etofenamate into the lumbar region as well as to the knee joint resulted in consistent serum levels: 219 +/- 136.3 micrograms/l and 191 +/- 84.6 micrograms/l, respectively. In patients with synovitis of the knee, the synovial level of etofenamate (368 +/- 109.2 micrograms/l) was almost twice as high than the serum concentration. The authors conclude that with topical application of etofenamate by iontophoresis the drug appears not only in the serum but also--with higher levels--in the synovial fluid.

Interrelation of permeation and penetration parameters obtained from in vitro experiments with human skin and skin equivalents

In a comparative study, two different in vitro cutaneous test systems were examined: (1) The Franz diffusion cell (FD-C), a test system to study drug permeation through the skin and to obtain data like steady state flux and lag time as well as permeability and diffusion coefficients. (2) The Saarbruecken penetration model (SB-M), a test system to investigate drug penetration into different skin layers and after varying incubation times to acquire values about the quasi steady state drug amounts in the stratum corneum (SC). Three drug concentrations (0.9, 0.45 and 0.225%) of a lipophilic model drug preparation, flufenamic acid in wool alcohols ointment, were applied on the skin's surface using 'infinite dose' conditions. Trypsin-isolated SC, heat-separated epidermis, full-thickness skin and reconstructed human skin (RHS) served as skin membranes in the FD-C, while the SB-M experiments were only carried out using full-thickness skin. Increasing steady state flux data and m(ss) values (steady state drug amount in the SC) were detectable after the application of rising drug amounts. Concerning the permeability of the used skin membranes in establishing barrier properties, the following rank order was observed: RHS>SC> or =epidermis>full skin. The flux data of the FD-C experiments for isolated SC, separated epidermis and RHS were linearly related with the m(ss) values of the SB-M investigations, allowing a direct comparison of permeation with penetration parameters. Concerning the drug amount in the SC, previous investigations succeeded in the establishment of an in vivo/in vitro correlation. Based on the results presented here, the prediction of drug amounts present in the SC after different incubation times in vivo is now possible after penetration as well as permeation experiments using the lipophilic model drug preparation, flufenamic acid in wool alcohols ointment.

Reconstructed skin equivalents for assessing percutaneous drug absorption from pharmaceutical formulations

Excised human skin has so far been considered to be one of the most suitable in vitro methods to evaluate the penetration of dermatologically applied substances. The limited supply and the relatively high donor variability stimulated many research groups to use animal skin as a substitute for human skin. Since nowadays reconstructed skin equivalents are commercially available, we examined these cultures for their suitability as a percutaneous absorption model for different pharmaceutical formulations. One such equivalent is EpiDerm (EPI-606, MatTek corporation, Ashland Massachusetts) which was investigated using the lipophilic model drug flufenamic acid. Permeation studies with the Franz diffusion cell were undertaken to evaluate the model for the establishment of a new in vitro method to study the percutaneous absorption of different dosage forms. The drug was applied in two pharmaceutical formulations to the intact surface of the skin disk: dissolved in wool alcohol ointment (0.1125 %), and dissolved in Soerensen phosphate buffer pH 7.4 (0.1125% solution). HPLC was used for the analysis of drug content. It was shown that the model forms a barrier towards diffusion by comparing the permeation across the tissue-free inserts to the equivalents. Flux values were calculated and the permeation across the skin equivalent from the solution was noted to be almost forty times higher than from the ointment. Two different batches of the skin equivalent showed no statistically significant difference. Finally the permeability of the reconstructed skin was compared to human epidermis, and a five times higher flux value was found for the skin equivalent model. Our results suggest that reconstructed skin equivalents based on human keratinocytes have potential as a pharmaceutical test system to study dermal drug transport from topical formulations.

Drug distribution in human skin using two different in vitro test systems: comparison with in vivo data

PURPOSE

Two in vitro test systems used to study drug penetration into human skin--the Franz diffusion cell (FD-C) and the Saarbruecken penetration model (SB-M)--were evaluated, and the results were compared with data gained under analogous in vivo conditions.

METHODS

Excised human skin was used in all in vitro experiments. Flufenamic acid dissolved in wool alcohols ointment, was chosen as a model drug, and the preparation was applied using 'infinite dose' conditions. To acquire quantitative information about the drug penetration, the skin was segmented into surface parallel sections at the end of each experiment, first by tape stripping the stratum corneum (SC), and second by cutting the deeper skin layers with a cryomicrotome. The flufenamic acid was extracted from each sample and assayed by high performance liquid chromatography (HPLC). For in vivo experiments, only the tape stripping technique was used.

RESULTS

a) Drug penetration into the SC: In both in vitro test systems the total drug amounts detected in the SC were found to increase over the different incubation times. Similar conditions were obtained in vivo, but on a lower level. Using Michaelis-Menten kinetics, the m(max) value was calculated for the skin of two donors. The relations of the m(max) values for the FD-C and the SB-M closely correspond (1.26 [donor 1] and 1.29 [donor 2]). A direct linear correlation of the drug amount in the SC and the time data were found for in vivo with both in vitro test systems. b) Drug penetration into the deeper skin layers: The detected drug amounts in the deeper skin layers continuously increased with the incubation time in the SB-M, while in the FD-C, only very small drug amounts were observed after incubation times of 30 and 60 minutes. It was also noticed, that the drug amounts rose steeply at time points 3 and 6 hours. Additional studies showed a remarkable penetration of water into the skin from the basolateral acceptor compartment in the FD-C. This could explain the different drug transport into the deeper skin layers between the two in vitro test systems.

CONCLUSIONS

Both in vitro models showed comparable results for the drug penetration into the SC and a robust correlation with in vitro data. Different results were obtained for the deeper skin layers. Whether a correlation between in vitro and in vivo data is also possible here has to be investigated by further experiments.

Statistical testing of drug accumulation in skin tissues by linear regression versus contents of stratum corneum lipids

This investigation is a contribution to standardization in in vitro drug penetration measurements using excised human skin and to statistical treatment of the observations. The wide variations observed in measurements of drug accumulation in and drug permeation through the stratum corneum are caused not only by analytical errors but also by the variability of the horny layer lipid composition. The last-mentioned systematic influence can be compensated for by stepwise (multiple) linear regression using the contents of the main lipid classes as independent variables. In consequence, the S.E. of estimate given by the regression calculation is lower than the S.E. of the means of the observations. Significant differences in drug quantities accumulated in skin tissues (stratum corneum and dermis) are sensitively detected by Chow's F-test of structural change. Accumulation data of flufenamic acid and hydrocortisone penetrated from different bases are given as examples. The calculation mode is exemplarily explained and discussed. The results of the test for structural change, two-independent-groups t-test and paired-samples t-test are compared. The F-test of structural change proves to be a helpful statistical method suitable to the assessment of biopharmaceutical quality parameters and to measurements using biological materials.

In vitro investigations of drug release and penetration--enhancing effect of ultrasound on transmembrane transport of flufenamic acid

Percutaneous absorption studies are performed in various in vitro models to determine the rate of drug absorption via the skin. We designed an phonophoretic drug delivery system to investigate the influence of ultrasound on transmembrane transport of different drugs. Phonophoresis is defined as the migration of drug molecules, contained in a contact agent, through the skin under the influence of ultrasound. We investigated the absorption of flufenamic acid in a buffer medium in dependence of ultrasound energy and application time. For evaluating membrane penetration of flufenamic acid, the concentration range of buffer solution was measured. Flufenamic acid was determined by using a fluorimetric method. Ultrasound energy was supplied for between 5 and 30 min at a range of intensities (0; 0.3; 0.6; 0.9; 1.2; 1.5 W/cm2). energy levels commonly used for therapeutic purpose. The pronounced effect of ultrasound on the transmembrane absorption of the drug was observed at all ultrasound energy level studied. The time of application was found to play an important role in delivery and transport of drug. Dependent on time, we observed an arise of temperature up to 4.5 degrees. It appears that there was no difference between an intensity of 0.3 and 1.5 W/cm2 and the measured drug concentrations in solution. The highest penetration was observed at an intensity of 1.0 W/cm2 after 30 min. These results were not significantly different from concentration in measurements after 30 min and 0.5 and 1.5 W/cm2. It seems that the arise of drug concentration is caused by effects of temperature and by variation of membrane delivery in dependence of temperature.

In vitro investigations of drug release and penetration--enhancing effect of ultrasound on transmembrane transport of flufenamic acid

Although topical drugs are usually applied at a convenient site, the target for the drug interaction may be systemic. Phonophoresis is the use of ultrasound to enhance the delivery of topical applied drugs. The purposes of our study were to investigate the in vitro penetration and the in vivo transport of flufenamic acid in dependence of ultrasound. Percutaneous absorption studies are performed in various in vitro models to determine the rate of drug absorption via the skin. We designed a phonophoretic drug delivery system to investigate the influence of ultrasound on transmembrane transport of different drugs. We investigated the absorption of flufenamic acid in a buffer medium in dependence of ultrasound energy and application time. For evaluating membrane penetration of flufenamic acid, the concentration range of buffer solution was measured. Ultrasound energy was supplied for between 5 and 30 min at a range of intensities up to 1.5 W/cm2, energy levels commonly used for therapeutic purpose. The pronounced effect of ultrasound on the transmembrane absorption of the drug was observed at all ultrasound energy levels studied. The time of application was found to play an important role in delivery and transport of drug. Dependent on time, we observed a rise of temperature up to 4.5 degrees C. It appears that there was no difference between an intensity of 0.3 and 1.5 W/cm2 and the measured drug concentrations in solution. The highest penetration was observed at an intensity of 1.0 W/cm2 after 30 min. These results were not significantly different from concentration measurements after 30 min and 0.5 and 1.5 W/cm2. It seems that the arise of drug concentration is caused by effects of temperature and by variation of membrane delivery in dependence of temperature. Using this in vitro model we note it is possible to compare the transdermal penetration and absorption of commercial flufenamic ointment in volunteers.

Sustained release of flufenamic acid from a drug-triacetyl-beta-cyclodextrin complex

Triacetyl-beta-cyclodextrin (TA-beta-CyD), a hydrophobic cyclodextrin derivative that is insoluble in water, was used to form a complex with flufenamic acid (FA). Complexes of FA with TA-beta-CyD (FA-TA-beta-CyD) at various molar ratios (1:1, 1:2, 1:3) were prepared by a kneading method, using ethanol as a solvent. FA-TA-beta-CyD complex formation was demonstrated by differential scanning calorimetry and powder X-ray diffractometry. The release rate of FA from the FA-TA-beta-CyD complexes was measured in both the Japanese Pharmacopoeia XII 1st fluid pH 1.2 and isotonic phosphate buffer pH 6.8. The release rate of FA from the FA-TA-beta-CyD complexes in the isotonic phosphate buffer pH 6.8 was significantly retarded compared to the release rate of FA from the FA-glucose mixture. After 1 h, 100% of the drug was released from the FA-glucose mixture and 10-25% was released from the complexes. When either the powder of the FA-glucose mixture or the FA-TA-beta-CyD mixture was administered directly into the intraduodenal lumen in rats, the plasma concentration of FA reached a maximum level within 40 min after administration. On the other hand, when the FA-TA-beta-CyD complexes were administered into the intraduodenal lumen, the plasma concentration of FA did not show a sharp peak, but remained at a plateau level (10-18 microg/ml) for 6-8 h. An increased mean residence time of FA following FA-TA-beta-CyD complexes administration was observed; however, the AUC(0-10) for the FA-TA-beta-CyD complexes showed no significant difference from that for the FA-TA-beta-CyD mixture. These results indicate that TA-beta-CyD may serve as a hydrophobic carrier in sustained-release preparations of FA. The drug-TA-beta-CyD complexes may therefore be useful in oral administration to achieve prolonged action and reduced side effects.

High-performance liquid chromatography of flufenamic acid in rat plasma

A simple high-performance liquid chromatographic (HPLC) method for the determination of flufenamic acid in rat plasma is described. After liquid-liquid extraction, the drug is separated by HPLC on a 5-microns octadecylsilica column (Nucleosil C18) with ultraviolet detection at 280 nm. Linear calibration graphs for flufenamic acid were constructed from 0.5 to 15 micrograms/ml. The method has been applied to a pharmacokinetic study in animals.

Synthesis of the cholesteryl ester prodrugs cholesteryl ibuprofen and cholesteryl flufenamate and their formulation into phospholipid microemulsions

Phospholipid micoremulsions have been suggested as a drug-delivery system for hydrophobic compounds. In this study hydrophobicity was achieved by derivatizing with cholesterol. Cholesteryl ibuprofen (3) and cholesteryl flufenamate (4) were synthesized. 3 was isolated as an amorphous, white solid with a melting range of 114-120 degrees C. 4 was isolated as a crystalline, white solid with a melting range of 145-148 degrees C. The proposed structures of 3 and 4 were supported by IR, NMR, MS, and organic microanalysis. Phospholipid:cholesteryl ester microemulsions were prepared by the addition of a 1-propanol solution of the cholesteryl ester, other lipids, and phospholipid to a rapidly mixing KCl/KBr solution. The hydrophobic phase was modified by the addition of cholesteryl oleate or triolein to study the effect of the fluidity of the hydrophobic core on the formation of the microemulsions. The results indicated that a molar ratio of 75:25 and a total lipid concentration of 60 mg/mL consistently gave microemulsions with a mean size of 100-150 nm. In addition, the formation of eutectic mixtures of 3 and 4 with cholesteryl oleate were determined to be 16% (w/w) for 3 and 12% (w/w) for 4; melting points were 35.2 and 45.2 degrees C, respectively. The solubilities of 3 and 4 in triolein were determined to be 13.2% (w/w) and 11.5% (w/w), respectively. Other investigators have shown that if the core of a phospholipid:cholesteryl estermicroemulsion exists in a liquid state at physiologic temperature, the turnover of the cholesteryl esters from these microemulsions occurs at a faster rate.(ABSTRACT TRUNCATED AT 250 WORDS)

The isolated perfused bovine udder as an in vitro model of percutaneous drug absorption. Skin viability and percutaneous absorption of dexamethasone, benzoyl peroxide, and etofenamate

Using udders from slaughtered cows as a new in vitro model of percutaneous drug absorption, the tissue viability and the percutaneous absorption of dexamethasone, benzoyl peroxide, and etofenamate were studied. The organ was perfused with gassed tyrode solution for up to 6 hr. As shown by measurement of glucose consumption, lactate production, lactate dehydrogenase activity, and pH in the perfusate, the tissue was viable over a 6-hr period. This was confirmed by a histological examination. Determination of the udder skin-fold thickness demonstrated that no edema developed within the perfusion period. A maximum skin penetration of dexamethasone was found after administration of dexamethasone dissolved in acetone with dimethyl sulfoxide, followed by ointment with salicylic acid, ointment without salicylic acid, and acetone solution. Experiments with benzoyl peroxide and etofenamate demonstrated that the perfused udder skin was capable of metabolizing drugs in vitro. In conclusion, the isolated perfused bovine udder is a new in vitro model, which maintains bovine udder skin with an isolated vasculature in a viable state. Using this in vitro model, we note it is possible to compare the dermal penetration, metabolism, and absorption of substances after topical administration of different drug formulations.

[Plasma- and tissue concentrations following intramuscular administration of etofenamat. Pharmacokinetics of etofenamat and flufenamic acid in plasma, synovium, and tissues of patients with chronic polyarthritis after administration of an oily solution of etofenamat]

Studies on Plasma and Tissue Concentrations of Etofenamate following Intramuscular Application/Pharmacokinetics of etofenamate and flutenamic acid in plasma, synovia and tissues of patients with chronic polyarthritis after application of oily etofenamat solution Pharmacokinetics of etofenamate (ETO, CAS 30544-47-9; Rheumon i.m.) and flufenamic acid (FLU, CAS 530-78-9) were investigated in plasma, synovial fluid, and tissues after single intramuscular application of etofenamate to patients with rheumatoid arthritis. 62 patients with indicated operative procedure in the knee-joint received a single dose of etofenamate dissolved in oil before operation. At definite times between 1.5 and 48 h post injectionem samples from 6 patients of each time group were collected. Samples of plasma, synovial fluid, synovial membrane, muscle, bone, hyaline cartilage, and fat tissue and in some cases meniscus cartilage were taken. Concentrations of ETO and its active metabolite, FLU, were determined by HPTLC. In all tissues investigated, concentration/time courses of ETO and FLU were observed. ETO and FLU were measured first in all matrices 1.5 h at the latest 3 h post injectionem. Pharmacokinetics in tissues follows that in plasma. Rate-limiting step is the liberation of drug from the oil depot. For a long period pharmacokinetics of ETO and FLU is mainly determined by the constant liberation from the oil depot (zero order kinetics of liberation). Zero order kinetics is deduced from the linear ascent of the cumulated AUC (in percent) vs. time plot. It is directly related to the liberation of drug from the galenical formulation.(ABSTRACT TRUNCATED AT 250 WORDS)

[Renal elimination and metabolism of etofenamate in volunteers after administration of various doses]

Renal Elimination and Metabolism of Etofenamate after Intramuscular Administration of Different Doses to volunteers. Renal elimination of etofenamate (active substance of Rheumon i.m.) after i.m. injection of oily solution of etofenamate to volunteers was investigated by HPTLC and GC. After injection of 250, 500 and 1000 mg etofenamate, free and conjugated flufenamic acid (flu), 5-hydroxy- and 4'-hydroxy flufenamic acid (5-OH-flu, 4'-OH-flu) were found as main metabolites in urine. Besides that several minor metabolites were identified. The ratio of free to conjugated metabolites was 1:10 to 1:25. From the doses administered 30% were eliminated as main metabolites. Overall amounts (in mg) of the eliminated metabolites and the doses correlated with each other (r = 0.9334), whereas the percent ratio of 5-OH-flu and of 4'-OH-flu increased with dose. Half lives of renal elimination for flu, 5-OH-flu and 4'-OH-flu are largely independent of dose. The half life of flufenamic acid corresponds roughly to data from plasma levels (7-9 h), the two hydroxy derivatives are eliminated into urine with half lives from 15 to 24 h. The results show, that i.m. injection of an oily etofenamate solution follows a linear dose independent kinetic, while the amounts absorbed and renally eliminated are proportional to dose. The results correspond to plasma level studies.

[Plasma level studies in volunteers after intramuscular injection of various doses of etofenamate in an oily solution]

Plasma level Studies on Volunteers after Intramuscular Application of Different Doses of Etofenamate in Oily Solution. After i.m. injections of etofenamate (active substance of Rheumon i.m.) in oily solution to 12 volunteers, courses of plasma levels of etofenamate, flufenamic acid and fenamate (sum of etofenamate and flufenamic acid) were measured by HPTLC. Maximum levels of etofenamate, flufenamic acid and fenamate, as well as areas under the plasma level time curve (AUC) after 250, 500 and 1000 mg etofenamate respectively are proportional to dose. Maxima of fenamate plasma levels are reached after 6.3, 6.2 and 5.4 h respectively, half maximal levels are present already after 2 h. The mean residence time is 21.8, 18.8 and 15.7 h. These values obtained from different doses are not statistically different from each other. Pharmacokinetics are therefore linear and dose independent. The courses of fenamate levels can be described by a two compartment model. The elimination half lives after 250, 500 and 1000 mg are 2.1, 2.3 and 1.9 h, the invasion half-lives (dominant half-life) 8.8, 7.8 and 6.8 h. Terminal half-lives are 50.3, 63.7 and 35.4 h. Since plasma levels have decreased to 2% of the maximum level after one terminal half-life, they have no practical importance for the duration of activity or for accumulation. No sex related differences are found for dose dependent and independent parameters. From the data it can be derived that after i.m. injection of etofenamate in oily solution a prolongation of the dominant half-life occurs by a factor of 4-5 (as compared to oral data) which is caused by prolonged liberation from the oily depot. This long lasting liberation of etofenamate leads to a prolonged residence time after a fast increase, at the same time avoiding unnecessary high peak levels. Therefore it is guaranteed that even after i.m. administration of 1000 mg etofenamate in oily solution plasma levels of fenamate do not exceed those after 300 mg given orally. According to pharmacokinetic data a fast onset of action, good tolerability and a therapeutic action over a period of 24 h can be expected.

[Animal experimental evidence of the long-lasting efficacy of etofenamate by prolongation of the half-life after intramuscular application]

Animal Experimental Evidence of Long-lasting Liberation of Etofenamate by Half-life Prolongation after Intramuscular Application. The purpose of this investigation was to show in animal experiments that by i.m. injection of etofenamate (active substance of Rheumon i.m.) in oily solution the following effects could be obtained: a fast onset of action (gain of therapeutically relevant drug levels shortly after injection) a long-lasting efficacy (prolonged liberation from the oil depot) and better tolerability as compared to other intramuscularly applicable antiinflammatory drugs (avoidance of high plasma spikes). Etofenamate in rats is liberated with a half-life of 1.29 days from the place of application (cutaneous half-life 8.5 h). Flufenamic acid in muscles is found only in traces. After i.m. administration of etofenamate to dogs maximum plasma levels of etofenamate and flufenamic acid were reached within 2 and 4 h, resp. The mean half-lives of plasma elimination are 14 h for etofenamate and 23.2 h for flufenamic acid formed esterolytically from etofenamate (flufenamic acid oral half-life 2-4 h). Maximum plasma levels after etofenamate are only 6.5-11.8% of the maximum levels after equivalent amounts of flufenamic acid administered orally. According to these data etofenamate i.m. is a drug formulation with fast increasing plasma levels, prolonged half-life and lower maximum plasma levels as compared to orally administered preparations. The results are confirmed in animals (pharmacodynamics, toxicology and tolerability) and man (kinetics, clinical studies).

[Anti-inflammatory and analgesic activity of etofenamate after intramuscular injection in laboratory animals]

Antiphlogistic and Analgetic Activity of Etofenamate in Laboratory Animals after Intramuscular Administration by injection of an oily solution of 10.5; 15; 19.5 mg etofenamate/kg body weight it was possible to inhibit the development of the carrageenan edema in the rat paw. Even four days after the single i.m. injection of etofenamate (active substance of Rheumon i.m.) the swelling of the rat paw is effectively prevented. By the Randall-Selitto-analgesia test it was possible to demonstrate the fast onset. Already 1 h after the injection of 15 mg/kg the pain threshold is increased to about 60%. Even in this testsystem the prolonged efficacy of oil diluted etofenamate can be found.

Effect of particle size and film thickness on bioavailability and ulcerogenicity of encapsulated flufenamic acid

Encapsulation of four batches of flufenamic acid (FFA) having mean particle diameters of 75, 130, 180 and 225 microns with cationic acrylic resin (Eudragit E) have been achieved using a fluidized-bed granulator (Glatt AG). The bioavailability and gastric ulcerogenic activity of the encapsulated and plain drug for each batch have been simultaneously assessed in rats subjected to physical restraint stress. Encapsulated batches of FFA showed significantly higher plasma levels and lower ulcerogenic activities than those of plain batches. Although encapsulated batches showed comparable plasma levels, compared with each other, they varied greatly as regards their ulcerogenic activities. The smaller the mean diameter of microcapsules of a batch the lower its ulcerogenic activity. A linear correlation was found between the film thickness of Eudragit in microcapsules and the ulcer indices of various encapsulated batches. Plain FFA batches, however, showed comparable plasma levels as well as comparable ulcer data, when compared with each other, within the size range studied.

Enhanced percutaneous penetration of flufenamic acid using lipid disperse systems containing glycosylceramides

The usefulness of lipid disperse systems, containing soybean phosphatidylcholine (PC) and glycosylceramide (GC) as lipid components, to enhance the percutaneous penetration of flufenamic acid (FA) through rat abdominal skin was examined by both in vitro permeation and in vivo absorption studies. The penetration of FA from a simple buffer suspension (pH 3.0) containing no lipid component was poor, but was markedly enhanced when FA was incorporated in PC-dispersions. However, this enhancing effect disappeared when the PC concentration in the preparation exceeded 40 mumol/ml. Enhanced penetration of FA from PC-dispersions could also be recognized when 30% propylene glycol or 30% glycerol was used as the dispersing medium instead of the aqueous buffer solution. Addition of GC to the PC-dispersions brought further enhancement of FA penetration through the skin. The maximal effect was observed when FA was incorporated in a 10%-GC system, and the cumulative amount of FA penetrating through the skin in 24 h from this system was approximately 6-fold larger than that from the simple buffer suspension. Enhanced absorption of FA from lipid disperse systems was also confirmed by in vivo application of these preparations.