International Journal of Pharmaceutics (v.243, #1-2)

Phonophoresis or sonophoresis is the use of ultrasound to increase percutaneous absorption of a drug. The technique has been widely used in sports medicine since the sixties. Controlled studies in humans in vivo have demonstrated absence or mild effects of the technique with the parameters currently used (frequency 1–3 MHz, intensity 1–2 W/cm2, duration 5–10 mins, continuous or pulse mode). However, it was demonstrated in 1995 that administration of macromolecules with conserved biological activity was feasible in animals in vivo using low frequency ultrasound. This led to new research into this method of transdermal administration. The aim of this review is to present the main findings published with low frequency and high frequency ultrasound over the last ten years, and to discuss the respective roles of thermal, cavitational and non-cavitational effects on the reduction of the skin barrier. Particular attention is paid to the biological effects on living skin which might be of importance for tolerance and practical use in humans.
Keywords: Administration; Cutaneous; Biological transport; Permeability; Pharmacology; Ultrasonics;

Enhanced drug dissolution using evaporative precipitation into aqueous solution by Marazban Sarkari; Judith Brown; Xiaoxia Chen; Steve Swinnea; Robert O Williams; Keith P Johnston (17-31).
A new process, evaporative precipitation into aqueous solution (EPAS) has been developed to coat poorly water soluble drugs, in this case carbamazepine, with hydrophilic stabilizers to enhance dissolution rates. A heated organic solution of the drug in dichloromethane is sprayed though a fine nozzle into a heated aqueous solution. The rapid evaporation of the organic solvent produces high supersaturation and rapid precipitation of the drug in the form of a colloidal suspension that is stabilized by a variety of low molecular weight and polymeric surfactants. The stabilizer adsorbs to the drug surface and prevents particle growth and crystallization during the spray process. The suspensions are dried by spray drying or ultra-rapid freezing. The high dissolution rates are a consequence of the following advantages of the EPAS process: a small primary particle size, a hydrophilic coating on the particles that enhances wetting, and low crystallinity.
Keywords: Carbamazepine; Dissolution rates; Particle engineering; Evaporative precipitation; Surfactant;

The formulation and the manufacturing process can significantly influence the photostability of tablets. Investigations of various formulation and manufacturing parameters were done with tablets containing nifedipine and molsidomine as highly light sensitive drugs. The effect of relevant formulation factors are stated. Whereas the particle size of the drug substance and the choice of the lubricant had no effect, the drug content, the compression diluent and geometric alterations significantly affected the photoinstability. Depending on the formulation drug losses varied between 30 and 55% after 12 h irradiation in a light testing cabinet (Suntest® CPS+). Manufacturing parameters like compression force and direct compression versus granulation showed less serious influences. Nevertheless, photostability changes up to 10% were registered.
Keywords: Photostability; Tablets; Nifedipine; Molsidomine; Formulation; Manufacturing process;

The encapsulation of ribozymes in biodegradable polymeric matrices by John K Jackson; Linda S Liang; William L Hunter; Mark Reynolds; Jennifer A Sandberg; Chris Springate; Helen M Burt (43-55).
Ribozymes are catalytic RNA that bind and cleave specific regions of target RNA. Therefore, protein synthesis by the target RNA may be specifically inhibited by ribozymes. However, ribozymes are rapidly cleared from plasma so effective treatment of proliferative diseases may rely on the repeated administration of these agents to maintain therapeutic ribozyme concentrations. Therefore, the objective of this study was to encapsulate ribozymes in injectable polymeric paste and microsphere formulations to allow for the controlled release of these agents over extended periods of time. Ribozymes were effectively encapsulated in poly(l-lactic acid) (PLLA) and poly(lactic-co-glycolic) (PLGA) microspheres in various size ranges using a modified water-in-oil-in-water emulsion system and in poly(ε-caprolactone) (PCL) pastes by physical blending. These formulations released non-degraded ribozymes, in vitro, in a controlled manner. PLLA microspheres released the ribozymes rapidly whereas PLGA released drugs more slowly. The release rate of ribozymes from PCL pastes could be effectively controlled by altering the loading concentration of ribozymes in the paste. These polymeric injectable formulations of ribozymes may allow for the extended treatment of localized disease sites, such as cancer and arthritis, without the need for repeated dosing.
Keywords: Ribozymes; Polymeric drug delivery; Controlled release; Poly(lactic acid); Polycaprolactone; Microspheres; Polymeric pastes;

Characterisation of water behaviour in cellulose ether polymers using low frequency dielectric spectroscopy by C.B. McCrystal; J.L. Ford; R. He; D.Q.M. Craig; A.R. Rajabi-Siahboomi (57-69).
The behaviour of water in hydroxypropylmethylcellulose (HPMC) K100LV, K4M, K15M, K100M, E4M, F4M and HPC polymers was characterised using low frequency dielectric spectroscopy (LFDS). Dielectric responses of 25% (w/w) HPMC K15M gels and deionised water were found to be similar at +22 and 0 °C. However, at −30 °C, a dielectric response typical of a solid was apparent. The melting of frozen water within gels was detected as increases in the magnitude of the dielectric response with increase in temperature. More than one phase transition was visible in the majority of gels studied which may be related to the presence of different states of water melting at different temperatures. In addition to polymer concentration, both polymer molecular weight and substitution level influenced the nature of the transitions. The magnitude of the dielectric response was increased in all HPMC gel systems in comparison to the response seen in deionised water. Drug addition affected the transitions occurring during the melting of ice in the gels. This may be related to the presence of ionic species in the systems. LFDS studies on cellulose ether gels have provided some interesting evidence for the existence of more than one state of water within such gel systems. The results are in good agreement with thermal analysis findings in similar gel systems.
Keywords: Hydroxypropylmethylcellulose; Cellulose ether; Low frequency dielectric spectroscopy; Water; Phase transitions;

Differential scanning calorimetry and scanning thermal microscopy analysis of pharmaceutical materials by Laura Bond; Stephanie Allen; Martyn C Davies; Clive J Roberts; Arif P Shivji; Saul J.B Tendler; Phillip M Williams; Jianxin Zhang (71-82).
Micro-thermal analysis (μTA) by scanning thermal microscopy is being used increasingly for the analysis of pharmaceutical dosage forms. However, there is currently little evidence to show that μTA data can compare directly with that from the established approach of differential scanning calorimetry (DSC). This work compares DSC and μTA data from an active vitamin B6 analogue, pyridoxal hydrochloride, and two commonly used pharmaceutical excipients, Mannitol and Avicel™ which are used in its formulation. It is found that μTA provides precise and accurate micro-thermal analytical data with 0.1 K thermal sensitivity, which is comparable to that obtained by DSC measurements of bulk samples. It is also shown that μTA offers the opportunity to study single particles and the interfacial region between particles, data which is currently inaccessible through the DSC technique.
Keywords: DSC; μTA; Excipient; Particle;

Rifampicin microparticles production by supercritical antisolvent precipitation by Ernesto Reverchon; Iolanda De Marco; Giovanna Della Porta (83-91).
Semi-continuous supercritical antisolvent (SAS) precipitation has been used to produce Rifampicin micro- and nanoparticles with controlled particle size (PS) and particle size distribution (PSD). SAS experiments were performed using different liquid solvents. The best micronization results have been obtained using dimethyl sulfoxide (DMSO); using this solvent and operating at 40 °C, we obtained nanoparticles with mean diameters ranging from 0.4 to 1 μm at a pressure of 120 bar or more, and microparticles with mean diameters ranging from 2.5 to 5 μm at pressures between 90 and 110 bar. The morphology of Rifampicin precipitates was different too. Nanoparticles connected in small aggregates were obtained at pressures higher than 120 bar, whereas, spherical single microparticles were obtained operating at lower pressures. We also investigated the effect of the concentration of Rifampicin in the liquid solution on particles diameter: we observed that, increasing the liquid concentration, the mean PS increased and the PSD enlarged. XRD and HPLC analysis on treated Rifampicin showed that particles are amorphous and no degradation occurred as a consequence of supercritical processing. We attempted an explanation of the different morphologies observed considering the modification of the high pressure vapor–liquid equilibria of the ternary system Rifampicin–DMSO–CO2 with respect to the behavior of the binary system DMSO–CO2.
Keywords: Rifampicin; Supercritical fluids; Microparticles; Antisolvent;

Preparation, characterization and biodistribution of ultrafine chitosan nanoparticles by Tanima Banerjee; Susmita Mitra; Ajay Kumar Singh; Rakesh Kumar Sharma; Amarnath Maitra (93-105).
Chitosan nanoparticles cross-linked with glutaraldehyde have been prepared in AOT/n hexane reverse micellar system. The cross-linking in the polymeric network has been confirmed from FTIR data. Because of the adhesive nature of these particles, their sizes, as measured by QELS, have been found dependent on the particle density in aqueous buffer. The particle size has also been found to vary with the amount of cross-linking. The actual particle size of these chitosan nanoparticles with a particular degree of cross-linking has been determined at infinite dilution of particles in water. The particle size at infinite dilution is ≈30 nm diameter, when 10% of the amine groups in the polymeric chains have been cross-linked and it shoots up to 110 nm diameter when all the amine groups are cross-linked (100% cross-linked). TEM pictures show that these particles are spherical in shape and remain in the form of aggregation. The biodistribution of these particles after intravenous injections in mice showed that these particles readily evade the RES system and remain in the blood for a considerable amount of time. The γ image of the rabbit after administration of 99mTechnetium (99mTc) tagged chitosan nanoparticles also confirms the above observation, as the blood pool is readily visible even after 2 h. The γ picture shows distribution of particles in the heart, liver, kidneys, bladder and the vertebral column. Interestingly, the biodistribution studies of the chitosan nanoparticles have indicated that these particles are distributed in the bone marrow also, implying the possibility of using these nanoparticles for bone imaging and targeting purpose.
Keywords: Chitosan nanoparticles; Gamma imaging; Biodistribution; Hydrogel polymers; 99mTechnetium;

Effect of inclusion complexation with cyclodextrins on photostability of nifedipine in solid state by Mohsen A Bayomi; Khalid A Abanumay; Abdulaziz A Al-Angary (107-117).
Nifedipine is a highly photosensitive drug that requires restricted protection from light during manufacturing, storage and handling of its dosage forms. Inclusion complexation of nifedipine with cyclodextrins (CDs) could be advantageous in protecting the drug against the effect of light. In this study, solid inclusion complexes of nifedipine with β-cyclodextrin (β-CD), hydroxypropyl-β-cyclodextrin (HP-β-CD) and dimethyl-β-cyclodextrin (DM-β-CD) were prepared using the coprecipitation method. The obtained solid inclusion complexes have been confirmed by differential scanning calorimetry (DSC), X-ray diffraction and infrared spectroscopy (IR). The IR spectra indicated partial inclusion of nifedipine molecules into CD cavities through the dihydropyridine ring. Inclusion complexation was also associated with a dramatic enhancement of drug dissolution with magnitudes depended on the type of CD. The effect of exposure to fluorescent lamp and sunlight on the photodegradation of uncomplexed and complexed nifedipine was tested. Photodegradation of nifedipine was monitored using a high performance liquid chromatographic (HPLC) assay method. Inclusion complexation of nifedipine showed to retard drug photodegradation as indicated by degradation rate constant lowering with values depended on light source and type of complexing agent. This effect was the least with β-CD compared with that of modified β-CD. It was also interesting to notice that inclusion complexation of nifedipine offered much higher protection against the effect of fluorescent lamp than that of sunlight. The obtained results suggests that the design of solid dosage forms of nifedipine such as a fast dissolving nifedipine tablets is possible with the advantages of low required light protection.
Keywords: Nifedipine; Cyclodextrins; Inclusion complexes; Fluorescent lamp irradiation; Sunlight irradiation; Photostability;

The aim of the present work was to evaluate the effect of sustained release of potassium chloride semi-solid matrices prepared with different kinds and added amounts of Gelucires by the in vitro dissolution test and in vivo oral absorption study, and compared with a commercial product (slow-K). The results indicating that the release rates of potassium from experimental formulations were dependent on the type of semi-solid matrices (Gelucires). The higher the melting point of the Gelucires was incorporated, the slower release rate of the active substance was observed. Moreover, the values of similarity factor of Formulae F05 and F09 versus the reference in three kinds of dissolution medium (f 2) were higher than 50, indicating that these experimental formulations had similar sustained release effects to the reference (slow-K) in dissolution test. In vivo study, the cumulative amount (mEq) of potassium excreted curve and the excretion rate curve of F05 and F09 were found to be similar to that of slow-K, and there were no significant differences (P>0.05) in the maximum excretion rate and the mean time to reach the maximum rate between formulations and slow-K, indicating that the potassium chloride sustained release dosage form could be prepared using the Gelucires as lipid excipients.
Keywords: Potassium chloride; Dissolution test; Gelucire; In vivo study;

Halloysite supplied from New Zealand was shown by electron microscopy to be composed mainly of hollow microtubules having typical dimensions of 2–3 μm long and 0.3/0.1 μm outer/inner diameter. Aggregates of microtubules, double tubules and occasional split or partially unrolled tubules were observed. Energy dispersive analysis showed the mineral to be composed mainly of aluminium, oxygen and silicon, with a low content of iron. The dehydrated state of the mineral was confirmed by XRD analysis, which was partially reversible using a rehydration procedure with subsequent exchange of the intercalated water gained by glycerol, but larger molecules including the drug, diltiazem HCl, failed to exchange. The surface charge was predominantly negative over most of the physiologically relevant pH range (>2) and the specific surface area of the material was very large (∼57 m2/g), indicating that the material has significant potential for extensive binding of cationic drugs. Removal of allophanc present by a hot alkali treatment had little effect on luminal porosity, which prior to treatment was estimated to be ∼0.25 ml/g by a mercury intrusion technique and consequently should be the major site for drug loading. Halloysite also extruded and spheronised well to form smooth round pellets as an aid to further formulation development, which rapidly disintegrated in water unless prevented by sintering at 200 °C.
Keywords: Halloysite; Microtubular; Physicochemical characterisation; Drug delivery;

Solid lipid nanoparticles (SLNs) have gained attention as a colloidal drug carrier, particularly for drugs with limited solubility. The poor aqueous solubility of all-trans retinoic acid (ATRA) has been a limiting factor in its clinical use. This study was undertaken to overcome the solubility limitation of ATRA by loading in SLNs. The physicochemical characteristics of ATRA-loaded SLNs were investigated by particle size analysis, zeta potential measurement, thermal analysis and HPLC determination of ATRA content. The mean particle size of ATRA-loaded SLNs could be reduced (1) by mixing EggPC and Tween 80 as a surfactant and (2) by increasing the total surfactant amount. The smallest mean particle size of SLNs was obtained with 50 mg/g surfactant mixture composed of 54:46% (w/w) EggPC:Tween 80 (154.9 nm). The zeta potential of SLNs could be increased by mixing EggPC, Tween 80 and DSPE-PEG in the surfactant mixture. The zeta potential of SLNs prepared with 50 mg/g surfactant mixture composed of 48:6:46% (w/w) of EggPC:DSPE-PEG:Tween 80 was −38.18 mV. ATRA could be loaded at 2.4% (percentage of lipid matrix) on these SLNs without impairing their physical stability. After freeze-drying, the mean particle size and polydispersity index of ATRA-loaded SLNs were only slightly increased (181.8 vs. 265.2 nm, 0.173 vs. 0.200). Furthermore, no significant change was observed in the SLN-loaded concentration of ATRA and the zeta potential of SLNs after freeze-drying. Taken together, SLN formulation of ATRA with similar characteristics to those of parenteral emulsions could be obtained even after freeze-drying.
Keywords: All-trans retinoic acid; Solid lipid nanoparticle; Stability; Freeze-drying;

Polymorphic behavior of an NK1 receptor antagonist by Y Wang; R.M Wenslow; J.A McCauley; L.S Crocker (147-159).
Four anhydrous polymorphic forms (I, II, III and IV) of an NK1 receptor antagonist, Compound A, have been discovered. The pure compound can exist as either Forms I or II at room temperature and Forms III or IV at elevated temperatures. The four polymorphs were characterized by differential scanning calorimetry (DSC), thermogravimetric analysis, X-ray powder diffraction (XRPD) and solid-state NMR spectroscopy (SSNMR). Polymorphic transformations in the solid phase were studied using DSC, hot stage XRPD, temperature-modulated SSNMR and hot stage optical microscopy. The solubilities of Forms I and II in tert-butyl acetate at different temperatures were measured and the relative stability of the two forms was established. The thermodynamic transformation temperatures between Forms I and III, as well as Forms II and IV, were estimated by DSC. Transformation from Form III to IV, which is undetectable in a normal calorimetric run, was revealed through careful thermal programming. An interesting conversion route from Form I, a more stable form at room temperature, to Form II, a less stable form at room temperature was discovered.
Keywords: NK1 receptor antagonist; Polymorphism; Solid phase transformation; Differential scanning calorimetry; X-ray powder diffraction; Solid state NMR;

Slow-release melarsoprol microparticles by Stéphane Gibaud; Adela Gaia; Alain Astier (161-166).
The present study compares two methods of preparation of microparticles of melarsoprol for the treatment of the human trypanosomiasis. Melarsoprol is poorly soluble in water and in organic media. Microparticles were formulated with modified O/W and W/O/W methods, Poly(ε-caprolactone) microparticles were prepared either with a suspension-in-oil-in-water (S/O/W) solvent evaporation method or by complexation of melarsoprol with methyl ß-cyclodextrin followed by a water-in-oil-in-water (WCD/O/W) solvent evaporation method. Results showed a poor incorporation of melarsoprol (2.89±0.20 μg mg−1) using the WCD/O/W process, while the S/O/W process allowed achieving 161±5 μg mg−1 and seemed to be very effective for the preparation of a sustained release form of melarsoprol. Moreover S/O/W microparticles showed a slow release of the drug in 70% of phosphate buffer pH 7.4, 0.1 M and 30% of propylene glycol (about 50% in 2 h and 80% after 7 h).
Keywords: Melarsoprol; Microparticles; Polymer; Sustained release; Poly(ε-caprolactone);

A model to represent solvent effects on the chemical stability of solutes in mixed solvent systems by A. Jouyban; H.K. Chan; M. Barzegar-Jalali; W.E. Acree (167-172).
The applicability of the combined nearly ideal binary solvent/Redlich–Kister (CNIBS/R–K) equation for quantification of solvent effects on the stability of a solute is shown employing the experimental data of three solutes in different aqueous binary solvents. The proposed model provides a simple computational method to correlate/predict the instability rate constant of a drug in mixed solvent systems. The accuracy of the model is compared with that of a model proposed by Connors and co-workers employing various methods including mean percentage deviation (MPD) as comparison criteria. The obtained overall MPD values for the proposed model to correlate and predict the instability rate constants are 2.05±1.44 and 4.41±3.21%, respectively, where the corresponding values for Connors’ model are 4.34±3.28 and 10.74±9.86%. The results suggest that by using only five experimental instability rate constants at different concentrations of the cosolvent in a binary mixture, it is possible to predict unmeasured values falling between data points within an acceptable error range.
Keywords: Chemical stability; Solvent effects; Mixed solvents; Mathematical model;

Noticeboard (173-176).