International Journal of Pharmaceutics (v.222, #2)

Mechanisms of transport across cell membranes of complexes contained in antitumour drugs by B. Szachowicz-Petelska; Z. Figaszewski; W. Lewandowski (169-182).
Various mechanism of antitumour drug transport across cell membranes has been described. Particular attention has been paid to a passive transport, active transport and multidrug resistance of complexes contained in antitumour drugs. A drug supply to the target site depends on the blood circulation within the tumour, on characteristic drug diffusion in the tissue, and also on binding protein. The physiologic transfer of hydrophilic compounds across the membrane is usually intermediated by means of a specific receptor or a carrier in that membrane, which facilitates the transport of compounds to and from the cell. Some drugs, e.g. doxorubicin and annamycin, can pass across the membrane by intermediacy of liposomes which exhibit a great activity in penetrating into tumour cells. The efficiency of antitumour drugs is limited by the appearence of resistance, i.e. by the lack of sensitivity of the cell to the administered drug. The presence in the membrane of specific proteins belonging to the ABC carriers group is postulated in a resistance theory; they would be responsible for ‘pumping out’ lipophilic drug molecules from the cell. Participation of high-energy ATP molecule is required by P-glycoprotein (Pgp) and by MRP protein described in this paper for their action. The mechanisms that are responsible for the cell resistance to drugs have been presented by analysing the resistance to antimetabolites, particularly to folate and fluoropyrimidine analogues, to alkylating agents, e.g. cisplatinum, and to heterocyclic compounds being responsible for so-called multidrug resistance.
Keywords: Transport; Cell membranes; Antitumour drugs; Multidrug resistance;

Substituted amylose polymers are prepared by reacting amylose chains with a suitable substituent such as 1,2-epoxypropanol (glycidol). Substituted amylose polymers are introduced as novel excipients for controlled release of bioactive materials. Since substituted amylose polymers are amylose-based polymers, they are subject to biodegradation by α-amylase enzymes present in the gastro-intestinal tract; thus, gamma spectroscopy is used to follow the release of the natural abundant rhenium (VII) oxide used as a drug model, and to test their resistance to α-amylase enzymatic degradation. Two substituted amylose solid dosage forms were prepared: (i) matrix system and (ii) dry-coated tablets. Matrix systems and dry-coated tablets maintained their structure, and controlled the release of [186Re] showing no significant degradation of tablets by α-amylase.
Keywords: Substituted amylose; Gamma spectroscopy; Rhenium VII oxide; Biodegradation; Controlled release;

Mucosal damage due to esophageal adhesion of pharmaceuticals is a continued concern to both health care providers and drug manufacturers. As a result of this concern, dosage forms are now being designed to exhibit minimal esophageal adhesion. Previous researchers have used an in-vitro porcine esophageal model to determine the propensity for formulations to adhere to the esophagus as an alternative to human scintigraphy studies. This study used a porcine esophageal adhesion model similar to that used previously to determine the adhesiveness of placebo bisphosphonate formulations. Results are analogous to those obtained by previous researchers, with film-coated tablets showing greater adhesiveness than uncoated tablets. These same tablet formulations were also evaluated previously by a human scintigraphy study, and the results were exactly opposite of those obtained using the in-vitro porcine model. In the human scintigraphy study, the film-coated placebo risedronate tablet had a faster transit time than an uncoated round placebo tablet. In conclusion, the in-vitro porcine esophageal model is not predictive of esophageal transit in man and gamma scintigraphy is the preferred method to evaluate esophageal transit.
Keywords: Esophageal adhesion; Risedronate; In-vitro pig esophageal model;

The enhancing effects of non-ionic surfactants on the permeation of piroxicam from the poloxamer gels were evaluated using Franz diffusion cells fitted with excised rat skins. The effectiveness of penetration enhancers, the ratio of piroxicam flux in the presence or absence of enhancers, was defined as the enhancement factor. Among the various non-ionic surfactants tested, polyoxyethylene-2-oleyl ether showed the highest enhancing effects with an enhancement factor of 2.84. To elucidate the mechanisms of the action of enhancers, thermal analysis and histological examinations were carried out. Thermal analysis reveals that various surfactants have different fluidizing effects on stratum corneum. Skin pretreated with the poloxamer 407 gels containing various surfactants showed a loosely layered stratum corneum and wide intercellular space.
Keywords: Permeation; Surfactants; Piroxicam; Poloxamer; Permeation enhancer; Rat skin;

Influence of radiation sterilization on the stability of trifluorothymidine by Ph Horsch; L Bigler; H.R Altorfer (205-215).
The influence of radiation sterilization on the stability of trifluorothymidine (TFT) was investigated. TFT was irradiated under ambient atmosphere with a 60Co-source and with an electron accelerator at 25, 50, and 100 kGy, respectively. The radiation-induced effects were determined by chromatographic and spectroscopic methods as well as potentiometrically with a fluoride selective electrode. TFT was moderately stable to ionizing radiation. The degradation induced by electron-beam irradiation was significantly (P=95%) smaller than by γ-irradiation. The radiolysis products amounted to about 0.25% after electron-beam irradiation at 25 kGy, and to about 0.50% after γ-irradiation, respectively. The main irradiation product was 5-trifluoromethyluracil (TFMU). In addition five further impurities were detected with HPLC. Identification of degradation products was performed using HPLC-ESI-MS. A degradation path of TFT after radiation sterilization was shown.
Keywords: Trifluorothymidine determination; Degradation; γ-irradiation; Electronbeam-irradiation;

The effect of α-tocopherol on the in vitro solubilisation of lipophilic drugs by P.B. Nielsen; A. Müllertz; T. Norling; H.G. Kristensen (217-224).
α-Tocopherol is an excellent solvent for many poorly soluble drugs. The aim of this work was to study whether or not the presence of α-tocopherol has an influence on the solubilisation of poorly soluble drugs in simulated intestinal fluids (SIF). The solubilising capacity of mixed micelles containing α-tocopherol towards three lipophilic drugs was investigated. The solubilisation of α-tocopherol in an aqueous micellar phase was increased by the addition of monoglycerides (MG) and free fatty acids (FFA), preferably of medium chain length, as compared to a simple bile salt solution. The addition of α-tocopherol to mixed micellar solutions seems to have an effect on the solubilising capacity, which can be correlated to the partition coefficient of the drug to be solubilised. A positive effect on the solubilisation of griseofulvin and felodipine was found. For a highly lipophilic drug (Lu28-179), a positive effect on solubilisation was observed only in media containing MG and FFA of medium chain length. Generally, α-tocopherol cannot be considered an important factor for the solubilisation of highly lipophilic drugs in SIF. The presence of lipolytic digestion products (LDP) of the proper chain length in relation to the drug to be solubilised is much more important.
Keywords: α-Tocopherol; Solubility; Lipolytic degradation products; Fatty acid chain length; Bile extract; Partition coefficient;

Evaluation of percutaneous absorption and skin irritation of ketoprofen through rat skin: in vitro and in vivo study by Pao-Chu Wu; Jin-Sheng Chang; Yaw-Bin Huang; Chee-Yin Chai; Yi-Hung Tsai (225-235).
The influences of different mechanisms of penetration enhancers (such as menthol, azone, ethanol and nonivarnide) regarding the percutaneous absorption and skin irritation of ketoprofen formulations through rat skin were investigated by in vitro and in vivo study. The skin irritation degree at the end of the experiment (10 h) was deterinined by pathologic biopsy and colorimetry methods. In vitro, the menthol showed the most potent enhancing effect. Furthermore, the enhancement effect of a combination of menthol and nonivamide was higher than that of their individual use alone. In vivo the formulation containing 0.05% nonivantide, 5% menthol and 20% ethanol showed a higher penetration rate and an acceptable degree of skin irritation compared to a commercial product (Formax plus® gel containing 3% ketoprofen), indicating that it could be used in the clinical situation.
Keywords: Ketoprofen; Azone; Nonivamide; Irritation; Colorimetry;

Physicochemical properties such as alkylating and carbamoylating activity and in vivo antimelanomic effects against B16 melanoma of the spin labeled (nitroxyl free radical containing) glycine nitrosourea (SLCNUgly) and its nonlabeled analogue (ChCNUgly), synthesized in our laboratory are studied and compared to those of antitumour drug 3-cyclohexyl-1-(2-chloroethyl)-1-nitrosourea (CCNU). We have demonstrated that introducing of glycine moiety in the nitrosourea structure in practice does not affect either alkylating or carbamoylating activity. On the other hand replacement of cyclohexyl moiety in ChCNUgly structure with nitroxyl free radical leads to a decrease in carbamoylating activity and an increase in alkylating activity. Compound ChCNUgly showed in vivo a higher antimelanomic activity against B16 melanoma in comparison with CCNU and SLCNUgly. It completely inhibited B16 melanoma growth (TGI=100%) at a dose 64.0 mg/kg. Moreover, we established that joint i.p. application in normal mice of SLCNUgly plus a new immunostimulator (C3bgp) formerly isolated in our laboratory led to a 75% restoration in immune function with respect to antibody production measured by Jerne hemolytic plaque assay. In contrast, no immunostimulation was found after joint application of C3bgp plus ChCNUgly or CCNU at the same experimental conditions. Based on these preliminary results, a possibility for developing of new combination immunochemotherapy schemes for treatment of human cancers is discussed.
Keywords: Spin labeled nitrosoureas; B16 melanoma; Immunostimulation; Nitroxyl free radical; C3bgp;

Magnetic resonance imaging investigation of the mixing-segregation process in a pharmaceutical blender by N. Sommier; P. Porion; P. Evesque; B. Leclerc; P. Tchoreloff; G. Couarraze (243-258).
Magnetic Resonance Imaging (MRI) was used to study the mixing process of binary mixtures of free flowing sugar beads in a Turbula® mixer. In order to make particles MRI-sensitive, some reference beads were doped with an organic oil. Doped and undoped particles were mixed and MRI was used to non-destructively image the particle bed for a given number of mixer rotations (N R), bead diameter ratio (R=d ref/d i ) and rotation speed (V). All the results were quantified on the basis of image analysis to characterise the degree of mixing. Studies showed that for binary mixtures of identical particle size, the mixing was complete after 30 rotations, whereas for beads of different size (R=2.8) a segregated steady state was obtained after nearly 10 rotations. Experiments revealed that segregation appeared as soon as R=0.9. Moreover, the lower the rotation speed, the more segregated the final state was. It appeared that for a filling level greater than 80%, dead regions appeared in the centre of the powder bed. In conclusion, when the particles are non-cohesive, the Turbula® blender perfectly mixes identical beads but segregation occurs for beads of different size after just a few rotations.
Keywords: Mixing; Segregation; Magnetic resonance imaging; Turbula®; Segregation index;

Poly-N-isopropylacrylamide (PNIPAAm) thermosensibility makes this polymer a very attractive candidate for controlled drug delivery systems. The polymer possesses a lower critical solution temperature (LCST) which was found to be around 32 °C in pure water, but which can be affected by the medium composition, i.e. presence of salts or surfactants. The knowledge of the effects of such substances on the LCST is very important while using PNIPAAm as a controlled drug delivery agent. The influence of a number of physiological and non-physiological salts and surfactants has been studied. The results obtained show that the addition of salts provokes an important decrease of the LCST of the polymer (salting out effect). A strong influence of the valence and of the size of the anions of the halide group was found. As to the surfactants, according to their type and concentration, a decrease or an increase of the LCST or even no effect at all were found. The effect of the GI secretions on the PNIPAAm phase separation temperature is also discussed.
Keywords: Poly-N-isopropylacrylamide; Thermoresponsive polymers; Salts; Surfactant; Controlled-drug delivery; Gastro-intestinal secretions;

Stability of ascorbyl palmitate in topical microemulsions by P Špiclin; M Gašperlin; V Kmetec (271-279).
Ascorbyl palmitate and sodium ascorbyl phosphate are derivatives of ascorbic acid, which differ in stability and hydro-lipophilic properties. They are widely used in cosmetic and pharmaceutical preparations. In the present work the stability of both derivatives was studied in microemulsions for topical use as carrier systems. The microemulsions were of both o/w and w/o types and composed of the same ingredients. The stability of the less stable derivative ascorbyl palmitate was tested under different conditions to evaluate the influence of initial concentration, location in microemulsion, dissolved oxygen and storage conditions. High concentrations of ascorbyl palmitate reduced the extent of its degradation. The location of ascorbyl palmitate in the microemulsion and oxygen dissolved in the system together significantly influence the stability of the compound. Light accelerated the degradation of ascorbyl palmitate. In contrast, sodium ascorbyl phosphate was stable in both types of microemulsions. Sodium ascorbyl phosphate is shown to be convenient as an active ingredient in topical preparations. In the case of ascorbyl palmitate, long-term stability in selected microemulsions was not adequate. To formulate an optimal carrier system for this ingredient other factors influencing the stability have to be considered.
Keywords: Ascorbyl palmitate; Sodium ascorbyl phosphate; Stability; Microemulsions; Topical;

Non steroidal anti-inflammatory agents (NSAIDs) such as diclofenac have very low aqueous solubilities and consequently salt formation may be used to enhance solubility and dissolution rate. In this study, we examined the physicochemical properties of three diclofenac salts, diclofenac sodium (DNa), diclofenac N-(2-hydroxyethyl)pyrrolidine (DHEP) and diclofenac diethylamine (DDEA), and their different solid state forms to determine the influence of salt form on solubility, dissolution rate and membrane transport. The equilibrium solubility of DDEA at 25 °C was determined as 33 mM, lower than the solubilities of DHEP (273 mM) and DNa (66 mM) previously reported (). In addition to the dihydrate form of DHEP previously characterised, monohydrate forms of DHEP and DDEA were identified. Intrinsic dissolution rate studies were used to determine the solubility ratios of the hydrated and anhydrous forms. The monohydrate form of DHEP was found to be 1.8 times less soluble than the anhydrate, whereas DDEA anhydrate was approximately 1.7 times as soluble as the monohydrate form. On investigation of the pH-solubility profile (25 °C) of DDEA, appreciable supersaturation (76 mM) relative to the theoretical profile, was detected at the pHmax. This contrasts with values of >800 and 67 mM for DHEP and DNa, respectively. The transport of salt solutions through a porous membrane (Visking®) was investigated. A linear relationship between concentration (mM) and rate of transport (mmol/h) was established for DNa and DHEP solutions. The mass transfer coefficient determined for DHEP was lower than that for the other two salts. Nevertheless, the maximum transport rate obtained for DHEP is almost six times higher than that obtained for DDEA.
Keywords: Diclofenac salts; N-(2-hydroxyethyl)pyrrolidine; Diethylamine; Sodium; Solubility; Dissolution; Membrane transport;

The use of scintigraphy to demonstrate the rapid esophageal transit of the oval film-coated placebo risedronate tablet compared to a round uncoated placebo tablet when administered with minimal volumes of water by Alan C Perkins; Clive G Wilson; Malcolm Frier; P.Elaine Blackshaw; Richard J Dansereau; Rachel M Vincent; Dietrich Wenderoth; Sheila Hathaway; Zhengqing Li; Robin C Spiller (295-303).
As our population ages, and the consumption of pharmaceutical products rises, the incidence of solid oral dosage forms lodging in the esophagus is likely to increase and may be formulation dependent. The aim of this study was to compare the esophageal transit of the commercial film-coated risedronate tablet and a round uncoated tablet resembling the alendronate 10 mg tablet which is reported to cause esophagitis if ingested with little to no water. Water volumes of 30 ml and 50 ml were selected as these volumes can detect formulations prone to esophageal adhesion and a habits and practice study showed that these volumes are within the range preferred by women (7–385 ml). A total of 28 healthy postmenopausal women completed the four-way crossover scintigraphy study. For both volumes of water, the film-coated placebo risedronate tablet had a statistically significant faster esophageal transit time than the uncoated placebo tablet (P=0.002 for 30 ml water and P<0.001 for 50 ml water). Among those taking the round, flat, uncoated tablet, five subjects had esophageal stasis (transit >20 s) and in three subjects the tablet remained in the esophagus at the end of the 10-min imaging period. No stasis was observed for the oval film-coated placebo risedronate tablet. This study demonstrates that tablet size, shape and coating are pharmaceutical parameters which can be controlled to minimize esophageal contact of a dosage form with esophageal tissue.
Keywords: Risedronate; Esophageal transit; Scintigraphy; Film-coating; Tablet;

Pharmacokinetics of acetaminophen in Hong Kong Chinese subjects by Ophelia Q.P. Yin; Brian Tomlinson; Albert H.L. Chow; Moses S.S. Chow (305-308).
The pharmacokinetics of acetaminophen have been well studied in different populations, especially in Caucasians. However, limited studies on acetaminophen pharmacokinetics have been conducted in the native Chinese and few such data have been reported in the English language literature. Previous published studies suggested that environmental and genetic factors may cause inter-individual difference in acetaminophen disposition, thus we investigated the pharmacokinetics of acetaminophen in Hong Kong Chinese subjects. A single 500 mg oral dose of acetaminophen was administered to 12 healthy male Chinese subjects under fasting conditions. Multiple blood samples were obtained after drug administration. Plasma acetaminophen concentrations were determined using HPLC, and its main pharmacokinetic parameters were generated. In comparison to other published data, acetaminophen half-life was considerably longer (15–62%), and oral clearance was lower (16–56%) in Hong Kong Chinese as compared to Australian Chinese, Caucasians (USA, UK, Australia), and subjects from Pakistan, Denmark, Spain and South Africa. Similarities however were found in the pharmacokinetic parameters between Hong Kong Chinese and Mainland Chinese subjects. The observed pharmacokinetic parameters of acetaminophen in Hong Kong Chinese subjects may be different from other ethnic populations. Further studies are needed to verify this hypothesis.
Keywords: Acetaminophen; Pharmacokinetics; Ethnic difference;

Notice Board (309-312).