International Journal of Pharmaceutics (v.213, #1-2)
Influence of chlorhexidine species on the liquid crystalline structure of vehicle by E Farkas; R Zelkó; Gy Török; I Rácz; S Marton (1-5).
The aim of this study was to investigate the influence of three chlorhexidine species, chlorhexidine base and its salts (diacetate and digluconate), on the physico-chemical features of liquid crystalline systems and on drug transport through lipophilic membranes. Nonionic surfactant, Synperonic A7 (PEG7-C13–15) was selected for the preparation of the liquid crystalline systems. Mixtures of different ratios of Synperonic A7 and water were prepared. The liquid crystalline systems were characterized using polarizing microscopy, small-angle neutron scattering and transmission electron microscopy. Membrane transport was also examined. The addition of chlorhexidine species to the liquid crystalline system modified the structure of the liquid crystalline system. As a result of liquid crystal–drug interaction, the solubility of chlorhexidine base and its diffusion through lipophilic membranes increased in comparison with those of the chlorhexidine salts.
Keywords: Liquid crystals; Clorhexidine base and salts; Transmission electron microscopy; Small-angle neutron scattering; Membrane transport;
Release performance of a poorly soluble drug from a novel, Eudragit®-based multi-unit erosion matrix by Ketan A Mehta; M.S Kislalioglu; W Phuapradit; A.W Malick; N.H Shah (7-12).
Mechanisms governing the release of drugs from controlled delivery systems are mainly diffusion, osmosis and erosion. For poorly soluble drugs, the existing mechanisms are limited to osmosis and matrix erosion, that are commonly observed in single unit matrix dosage forms. This study reports formulation and dissolution performance of Eudragit® L 100 55 and Eudragit® S 100 based multi-unit controlled release system of a poorly soluble thiazole based leukotriene D4 antagonist, that was obtained by an extrusion/spheronization technique. Effect of triethyl citrate, that was incorporated in the matrix, on the dissolution performance of the drug was also evaluated. In vitro matrix erosion and drug release from the pellets were determined by the use of USP Dissolution Apparatus I, pH 6.8 phosphate buffer, gravimetry and UV spectrophotometry, respectively. Results obtained demonstrated that matrix erosion and drug release occurred simultaneously from the pellets. Pellets eroded with a consequent reduction in size without any change in the pellet geometry for over 12 h. Matrix erosion and drug release followed zero order kinetics. Data obtained strongly suggested a polymer controlled, surface erosion mechanism.
Keywords: Extrusion/spheronization; Eudragit® L 100-55; Eudragit® S 100; Surface erosion; Effect of plasticizer; Pellets; Controlled release;
Production and evaluation of size reduced grades of microcrystalline cellulose by S.R Levis; P.B Deasy (13-24).
Size reduction of microcrystalline cellulose (MCC, Avicel® PH-101) powder by ball milling was poorly effective, particularly in the presence of sodium lauryl sulphate (SLS), which tended to form a protective foam. Ultrasonic homogenisation of an aqueous suspension more readily produced ultra-fine MCC, even in the presence of the surfactant and two other de-aggregating agents, and factorial experimentation was used to optimise the process. The product was recovered by spray-drying and readily redispersed in water without re-aggregation. Two new grades of ultra-fine MCC, prepared by an optimised treatment with or without 1% SLS, were characterised by a range of techniques in comparison to the starting coarser grade, Avicel® PH-101. Mercury porosimetry and scanning electron microscopy confirmed the less porous and smaller particle size of the new grades, where deposition of SLS as a coating was evident. Surface area determination confirmed that the size-reduced grades had larger specific surface areas, particularly the SLS treated material. Low temperature DSC and X-ray diffraction studies suggested that the new ultra-fine grades were more amorphous. Collectively the results indicate that the new grades should have unique functionality, possibly of benefit in pharmaceutical formulation.
Keywords: Microcrystalline cellulose; Ultra-fine grades; Ultrasonic homogenisation; Sodium lauryl sulphate; Characterisation;
Solubilization of rapamycin by Pahala Simamora; Joan M Alvarez; Samuel H Yalkowsky (25-29).
The solubilization of rapamycin, a poorly water soluble investigational immunosuppressive drug, by facilitated hydrotropy is presented. Partially water-miscible aromatic solutes (such as benzyl alcohol, benzoate, or benzoic acid) can be solubilized by water-miscible cosolvents, such as ethanol and propylene glycol. Once solubilized, the partially miscible aromatic solute becomes a solubilizing agent. This technique yielded a dramatic (>1000-fold) increase in the aqueous solubility of rapamycin.
Keywords: Solubilization; Rapamycin; Solubility; Cosolvent; Hydrotrope; Hydrotropy;
A new application for the Antoine equation in formulation development by Koustuv Chatterjee; David Dollimore; Kenneth Alexander (31-44).
Characterization of formulation components in pre-formulation and formulation studies will be made easier if a rapid method to evaluate the evaporation characteristics of an ingredient in the formulation is developed. This study aims at providing a simple and rapid thermogravimetric method for estimating the vapor pressure characteristics using the Antoine equation as the analytical tool. The heat treatment for the majority of benzoic acid derivatives follows zero-order rate processes that are in good correlation with their evaporation process. The optimum conditions for the rising temperature experiments were found when the heating rate was 10°C/min in an atmosphere of dry nitrogen (100 ml/min). Methyl paraben was taken as the calibration compound since its Antoine constants are reported in the literature, and its selected thermodynamic parameters were evaluated using the Langmuir equation. The coefficient of vaporization ( k ̄ ) was determined to be 124 525±0.8, with units being reported in the S.I. system. The corresponding vapor-pressure plots were obtained for the remaining compounds and their Antoine constants calculated.
Keywords: Antoine equation; Langmuir equation; Parabens; Thermogravimetry; Vapor pressure;
Thermodynamic analysis of compact formation; compaction, unloading, and ejection by Mark T DeCrosta; Joseph B Schwartz; Rodney J Wigent; Keith Marshall (45-62).
A compaction calorimeter, previously described (DeCrosta, M.T., Schwartz, J.B., Wigent, J.B., Marshall, K., 2000. Thermodynamic analysis of compact formation; compaction, unloading, and ejection. I. Design and development of a compaction calorimeter and mechanical and thermal energy determinations of powder compaction. Int. J. Pharm. 198, 113–134), was utilized to evaluate the thermodynamics of the unloading and ejection of compacts of Avicel® pH102, Emcompress®, Fast-Flo #316®, Starch 1500, and acetaminophen (APAP). A constant strain waveform, applied by a compaction simulator, enabled the separate thermodynamic evaluation of unloading from compaction. The brittle materials, Fast-Flo #316® and Emcompress®, displayed the most unloading work, and the plastic/self-lubricating materials, Avicel® and Starch 1500, displayed the least. Unloading heat values were negative for all materials, except APAP. APAP's positive heat values indicated the breaking of bonds during unloading as a result of its highly elastic nature. Positive internal energy changes of unloading, which indicate the net breaking of bonds, were observed for APAP and Emcompress® over the compaction forces tested. Negative energy changes for Starch 1500, Fast-Flo #316®, and Avicel® became positive with increasing compaction forces. Ejection work increased with increasing compaction force for the brittle materials, whereas smaller ejection work values for Avicel®, Starch 1500, and APAP remained constant. Increasing negative heat values as a function of compaction force were observed for Fast-Flo #316® and Emcompress®. Negative internal energy values for ejection were observed for Fast-Flo #316® and Emcompress®, which indicates net bond formation as a result of high shear of the compact with the die wall. Internal energy changes for Starch 1500, Avicel®, and APAP, were approximately zero, indicating the absence of net bonding or bond formation during the process.
Keywords: Calorimetry; Compaction; Compaction calorimeter; Decompression; Decompression heat; Decompression work; Ejection; Ejection heat; Ejection work; Heat; Internal energy change; Percent porosity; Percent solids; Unloading; Unloading heat; Unloading work; Work;
An improved method for the measurement of colour uniformity in pellet coating by L.W Chan; W.Y Chan; P.W.S Heng (63-74).
Sucrose pellets in the size range of 0.71–0.85 mm were film-coated in a bottom-spray Wurster fluidised bed coater with a colour coating suspension of 7.5% w/w solids. Hydroxypropyl methylcellulose was used as a film former, polyethylene glycol as a plasticiser and yellow iron oxide as a coloured pigment. The colour distribution on the film coat was analysed using a tristimulus colorimeter and the colour value was measured in CIELAB units. Uniformity in the colour coat was indicated by the standard deviation of the colour measurement values. Four different methods for measuring the colour distribution over the colour coated pellets’ surfaces were carried out. In method I, colour measurements of the pellets’ surfaces were made by placing the pellets directly on the stage of the tristimulus colorimeter. A specially designed pellet sample holder was employed to assist the collection of colour measurements in methods II–IV. Colour measurements from eight spots on each pellet were taken in methods I, II and IV while method III involved measuring 24 spots per pellet. A total of eight overlapping spot measurements were taken in method IV while the eight spot measurements in method II were non-overlapping. Method II was found to be the most efficient, accurate and sensitive method for the measurement of spot colour distribution on pellets.
Keywords: Tristimulus colorimeter; Fluidised bed; CIELAB units; Coating; Colour uniformity;
Solubilization of tropicamide by hydroxypropyl-β-cyclodextrin and water-soluble polymers: in vitro/in vivo studies by Brunella Cappello; Claudia Carmignani; Maria Iervolino; M Immacolata La Rotonda; M Fabrizio Saettone (75-81).
1% (w/v) aqueous solutions of tropicamide (TR), a poorly water-soluble mydriatic-cycloplegic drug, are usually obtained by adjusting the pH to ∼5.0, at the expense, however, of ocular tolerance and bioavailability. The capacity of hydroxypropyl-β-cyclodextrin (HP-β-CD) to solubilize TR in pH 7.4 0.02 M phosphate buffer was investigated in the absence and presence of hydrophilic polymers (PVP, CMC and HPMC). Approximately 3.5% (w/v) HP-β-CD was required to solubilize 1% (w/v) TR in pH 7.4 buffer at room temperature. The required amount was reduced to 0.9% (w/v) by heating at 120°C in the presence of 0.1% (w/v) HPMC. Mydriatic activity tests in rabbits showed an improved bioavailability and maximal mydriatic response for two CD formulations, with and without HPMC, when compared to standard 1% (w/v) TR eyedrops, buffered at pH 5.0. The improved in vivo behaviour of the CD formulations are likely due to their physiological pH, resulting in a reduced irritant effect, although an effect of HP-β-CD on corneal permeability cannot be dismissed a priori.
Keywords: Tropicamide; Hydroxypropyl-β-cyclodextrin; Solubilization; Polyvinylpyrrolidone; Carboxymethylcellulose; Hydroxypropyl methylcellulose; Ophthalmic vehicles; Mydriatic effect; Rabbits;
A novel pH- and time-based multi-unit potential colonic drug delivery system. I. Development by Vishal K. Gupta; Thomas E. Beckert; James C. Price (83-91).
A novel delivery system was developed for delivering drugs to the colon by selecting polymethacrylates with appropriate pH dissolution characteristics for the distal end of the small intestine and relying upon the relatively constant transit time of the small intestine. Pellets were prepared by powder layering of 5-aminosalicylic acid (5-ASA) on nonpareils (0.5–0.6 mm) in a conventional coating pan. Drug-layered pellets were coated with an inner layer of a combination of two pH-independent polymers Eudragit® RL and RS (2:8), and an outer layer of a pH-dependent polymer, Eudragit FS. Scanning electron micrograph (SEM) pictures of the coated pellets showed the uniformity of both the coatings. The release profile of 5-ASA was studied in three phosphate buffers after a simulated gastric pre-soak for 2 h in pH 1.2 media. There was no drug release for 12 h at pH 6.5. There was a sustained release of 5-ASA for over 12 h both at pH 7.0 and 7.5 after a lag time at pH 7.0 and no lag time at pH 7.5. The release rate was faster at pH 7.5 than at pH 7.0. The delivery system demonstrated its potential for colonic delivery by resisting drug release until pH 6.5 and the combination of Eudragit RL and RS proved successful for the sustained delivery of 5-ASA at the expected pH of the colon.
Keywords: Controlled-release; Site-specific delivery; Colonic delivery; Pellets; Polymethacrylates; Eudragit;
A novel pH- and time-based multi-unit potential colonic drug delivery system. II. Optimization of multiple response variables by Vishal K Gupta; Manfred W Assmus; Thomas E Beckert; James C Price (93-102).
The objective of this work was to optimize a novel potential colonic drug delivery system by using a statistical procedure. Pellets were prepared by powder layering of 5-aminosalicylic acid (5-ASA) on nonpareils (0.5–0.6 mm) in a coating pan. Drug-layered pellets were coated with an inner layer of a combination of Eudragit® RL and RS and an outer layer of Eudragit FS in a fluidized-bed apparatus. Central composite design was used to study the effect of three independent variables. The proportion of the more hydrophilic polymer Eudragit RL had the most significant effect on drug release – higher proportion gave faster release; the amount of inner and outer coat did not have a significant effect on the rate of drug release at either 6 or 12 h in the range studied. A second order polynomial equation was fitted to the data, and the resulting equation was used to predict the responses in the optimal region. An optimized formulation was prepared and evaluated for individual responses. The experimental values of the response variables highly agreed with the predicted values. The results demonstrated the reliability of the model in the preparation of coated pellets having predictable drug release for colonic delivery of 5-ASA.
Keywords: Controlled-release; Colonic delivery; Optimization; 5-aminosalicylic acid; Polymethacrylates; Eudragit;
Effect of cross-linking on the in vitro release kinetics of doxorubicin from gelatin implants by Haiyun Fan; Alekha K Dash (103-116).
Doxorubicin is one of the most potent anti-tumor agents used generally in the treatment of bone cancer. Like other cancer chemotharepeutics, it produces undesirable side effects such as cardiotoxicity, which is especially severe when administrated via the conventional intravenous route. In order to minimize the systemic toxicities and to make this drug more suitable for the treatment of bone cancer, an implantable delivery system with cross-linked gelatin as the biodegradable matrix material was developed. This delivery system could possibly improve targeting of the drug as well as sustain the rate of release of the drug to the tumor. Glutaraldehyde was used as a cross-linking agent. Incorporation of glutaraldehyde in the matrix was needed to maintain the mechanical strength of the implant and to sustain the rate of release of the drug from the implant. Besides cross-linking the gelatin matrix, glutaraldehyde was found to cross-link the free amino group of doxorubicin. The effect of cross-linker concentration on the stability of the drug in the implant and on the rate and extent of release were also evaluated. In conclusion, cross-linked gelatin implants were developed for the local delivery of doxorubicin.
Keywords: Doxorubicin; Cross-linked gelatin; Implant; Glutaraldehyde;
Potential use of gelcasting hydroxyapatite porous ceramic as an implantable drug delivery system by D.J.A Netz; P Sepulveda; V.C Pandolfelli; A.C.C Spadaro; J.B Alencastre; M.V.L.B Bentley; J.M Marchetti (117-125).
Hydroxyapatite (HA) ceramic in a porous configuration is suggested as a drug release system. A new technique for the production of this material, based on the foaming of suspensions and in situ polymerization (gelcasting method), resulted in a material whose characteristics are likely to make it useful as an implantable drug delivery system. Three batches of HA ceramic with different porosities were characterized by X-ray diffraction and scanning electron microscopy (SEM). Pore size and shape as well as density were determined. In vitro experiments were performed in order to evaluate the dissolution behavior of cisplatin in the system. X-ray diffraction analysis showed that the final product consisted of a single phase, indicating that the sintering process had not affected the structure of the HA. Energy dispersive X-ray analysis (EDX) showed absence of impurities. Pore diameters were in the range 15–34 μm. SEM showed that the material presented a highly interconnected spheroidal porous network with open micropores and closed macropores. In vitro experiments showed significant differences in the release rate of cisplatin between three different porosities.
Keywords: Hydroxyapatite; Porous ceramic; Implantable drug delivery systems; Gelcasting;
Physicochemical and biopharmaceutical characterization of BTA-243, a diacidic drug with low oral bioavailability by J.R. Brown; J.H. Collett; D. Attwood; R.W. Ley; E.E. Sims (127-134).
This investigation has examined possible causes of the poor bioavailability of the beta3-adrenoceptor agonist BTA-243. The aqueous solubility of BTA-243 is pH dependent with a solubility minimum at pH 1.5. However, the dissolution rate of the disodium salt of BTA-243 is similar at both pH 2.0 and 7.4 indicating that dissolution rate is unlikely to be the controlling factor in the absorption of BTA-243. The apparent permeability coefficient of BTA-243 across Caco-2 monolayers at pH 6 was lower than that of mannitol and therefore the epithelial permeability of the molecule in vivo is predicted to be very low and potentially bioavailability limiting. Apparent permeability coefficients were not dependent on BTA-243 concentration over the concentration range 0.5 to 12 mM, indicating that epithelial transport is unlikely to occur via a saturable mechanism. They were of similar magnitude in both directions across the monolayers, indicative of no significant effluxing of BTA-243 by components of the cell membrane. Apparent octanol/water distribution coefficients increased with decrease of pH between 2 and 6; the relatively low values at pH 4 and 6 suggest that the limited intestinal absorption predicted in vivo will occur predominantly via paracellular passive diffusion. Everted gut sac experiments performed at pH 2.0 and 6.8 suggest that at pH 2.0 a significant proportion of the BTA-243 transport occurs via the transcellular route confirming that the ionization state of the BTA-243 molecule influences the route and rate of epithelial permeability.
Keywords: BTA-243; Solubility; Dissolution rate; Caco-2 cells; Permeability coefficients; Distribution coefficients; Everted gut sac;
Effects of calcium and lipophilicity on transport of clodronate and its esters through Caco-2 cells by Johanna Raiman; Riku Niemi; Jouko Vepsäläinen; Kirsi Yritys; Tomi Järvinen; Jukka Mönkkönen (135-142).
Clodronate, like other bisphosphonates, is poorly absorbed from the gastrointestinal tract, mainly due to its high hydrophilicity and ability to form complexes with divalent cations in the gastrointestinal tract. One strategy for improving oral absorption of these types of molecules is to develop more lipophilic derivatives. The importance of lipophilicity and calcium chelation in the absorption of clodronate was evaluated by studying the penetration of clodronate and its mono-, di-, and triphenyl esters through human intestinal Caco-2 cells. The transport rates of [14C]-clodronate and its mono-, di-, and triphenyl esters were quantified by calculating their apparent permeability coefficients (P app) both in normal (1.3 mM) calcium concentration and in ‘minimum-calcium model’. The transport rate of 1 mM clodronate was very low (0.25×10−7 cm/s), while the removal of calcium from the apical side increased this transport rate 6-fold. The transport rate of clodronate was increased with increasing dose. Mono- and diphenyl esters did not significantly enhance the transport of clodronate. Triphenyl ester, however, increased the transport rate 17-fold compared with parent clodronate. Removal of calcium did not affect the transport rates of di- or triphenyl esters, which indicated that the esterification of hydroxyl groups of clodronate decreased calcium complex formation. These results indicate that clodronate is transported paracellularly through Caco-2 cells and that calcium decreases strongly its absorption. They further suggest that at least three phosphate hydroxyl groups need to be substituted until the permeation route is changed from paracellular to transcellular.
Keywords: Clodronate; Bisphosphonates; Caco-2 cells;
Synthesis and characterisation of inulin-azo hydrogels designed for colon targeting by B Maris; L Verheyden; K Van Reeth; C Samyn; P Augustijns; R Kinget; G Van den Mooter (143-152).
The present paper describes the synthesis and characterisation of new hydrogel systems designed for colon targeting. The gels were composed of methacrylated inulin (MA-IN), copolymerized with the aromatic azo agent bis(methacryloylamino)azobenzene (BMAAB) and 2-hydroxyethyl methacrylate (HEMA) or methacrylic acid (MA). The gels were assessed by studying the influence of various parameters on the dynamic and equilibrium degree of swelling. It was shown that the uptake of water in the gels was inversely proportional to the MA-IN feed concentration, the degree of substitution of the inulin backbone, and the concentration of BMAAB. The latter can probably be explained by the hydrophobic nature and rigidity of the aromatic azo agent. Incorporation of the hydrophilic monomers HEMA or MA also reduced the equilibrium degree of swelling. An increasing network density and hydrogen bonding propensity, can suggested to be responsible for this observation. It was shown that water uptake in the hydrogels was controlled by both relaxation and diffusion mechanisms (anomalous behaviour). When the release of the model drug prednisolone was studied in phosphate buffer, it was shown that >80% of the drug was released during the first 3 h from hydrogels of MA-IN:HEMA. Although drug release decreased significantly from MA-IN:HEMA:BMAAB hydrogels, it remained too high: ∼50% of the drug was released after 5 h. The same observation was made for hydrogels containing MA instead of HEMA. These results clearly point out the difficulty in finding the optimal balance between swelling to allow degradation in the colon (high swelling of the gels) and low premature drug release before the colonic environment is reached (low swelling properties).
Keywords: Colon targeting; Azo polymers; Hydrogels; Inulin;
Pharmacokinetics of liposomal amphotericin B in neutropenic cancer patients by Türkan Eldem; Nermin Arican-Cellat; Ilbeyi Agabeyoglu; Murat Akova; Emin Kansu (153-161).
This study was conducted to characterise the pharmacokinetics of a liposomal pharmaceutical product of amphotericin B (LAB) in three neutropenic cancer patients complicated by suspected fungal infections. LAB was administered at a constant dose of 50 mg/day over 1–6 h by intravenous infusion, and blood samples were obtained between two infusion intervals without complicating the systemic therapy of the patients. Quantitative analysis of amphotericin B (AB) in plasma was established by a validated reversed-phase high-performance liquid chromatographic (HPLC) assay. Model independent pharmacokinetic parameters were estimated using area and moment analysis. Administration of LAB to the first patient (day 1) diagnosed as malignant melanoma resulted in a mean maximum concentration (C max) of 679±6 ng/ml and a mean minimum concentration (C min) of 139±9 ng/ml of AB. Pre-dose, C max and C min values of AB, after multiple LAB dosing to the other two patients both having acute myeloblastic leukemia were found to be 440±6, 1140±10, 409±11 ng/ml (day 19) and 408±3, 1180±10, and 283±1 ng/ml (day 9), respectively. The area under the plasma concentration–time curve (AUC) and the mean residence time (MRT) calculated between the two infusion intervals were 6180 ng h/ml, 7.79 h (day 1) for the first patient; 13 700 ng·h/ml, 10.5 h (day 19) and 14 000 ng·h/ml, 9.93 h (day 9) for the other two patients, respectively. The pharmacokinetic profiles and non-compartmental parameters calculated were comparable for both patients diagnosed with acute myeloblastic leukemia after multiple dosing at steady state, which also demonstrated a twofold increase in their AUC values compared with the AUC of the first patient. Although C min values supported the assumption that there was AB accumulation in plasma and this accumulation could be increased at high doses, LAB was administered safely to these patients and well tolerated at the doses given.
Keywords: Amphotericin B; Liposomes; Clinical pharmacokinetics; Neutropenic cancer patients;
Characterization of glassy itraconazole: a comparative study of its molecular mobility below T g with that of structural analogues using MTDSC by K. Six; G. Verreck; J. Peeters; P. Augustijns; R. Kinget; G. Van den Mooter (163-173).
The objective of the present study was to estimate the molecular mobility of glassy itraconazole below the glass transition, in comparison with structural analogues (i.e. miconazole and ketoconazole).Glassy itraconazole and miconazole were prepared by cooling from the melt. The glassy state of the drug was investigated with modulated temperature DSC using the following conditions: amplitude ±0.212 K, period 40 s, underlying heating rate 2 K/min. The glass transition was determined from the reversing heat flow and occurred at 332.4 (±0.5) K and 274.8 (±0.4) K for itraconazole and miconazole, respectively. The jump in heat capacity at the glass transition was 303.42 (±3.43) J/mol K for itraconazole and 179.35 (±0.89) J/mol K for miconazole. The influence of the experimental conditions on the position of the glass transition of itraconazole was investigated by varying the amplitude from ±0.133 to ±0.292 K and the period from 25 to 55 s, while the underlying heating rate was kept constant at 2 K/min. Glass transition temperature, T g, was not significantly influenced by the frequency of the modulation nor by the cooling rate. However, the relaxation enthalpy at the glass transition increased with decreasing cooling rate indicating relaxation during the glass formation process. To estimate the molecular mobility of the glassy materials, annealing experiments were performed from T g−10 to T g−40 K for periods ranging from 15 min to 16 h.Fitting the extent of relaxation of glassy itraconazole to the Williams–Watts decay function and comparing the obtained values with those of amorphous miconazole and ketoconazole indicated that the molecular mobility is influenced by the complexity of the molecular structure. The more complex the structure, the more stable the amorphous state.
Keywords: Itraconazole; Modulated temperature DSC; Molecular mobility; Amorphous drugs;
Factors involved in the production of liposomes with a high-pressure homogenizer by Ramon Barnadas-Rodrı́guez; Manuel Sabés (175-186).
A variety of factors were evaluated in order to establish the characteristics of the liposomes obtained with a high-pressure homogenizer (Microfluidizer 110S). The experimental mean diameter of the liposomes and the width of their size distribution were correlated to surfaces calculated from the responses obtained by the combination of two groups of factors. First, the inlet pressure of the homogenizer, the times that the samples were processed (cycles) and the bulk ionic strength. Second, the phospholipid (P) and ethanol concentrations. The variation of the entrapped liposome volume upon the pressure and cycles was also studied. All the calculated surfaces are statistically significant and have a low S.E. of estimate. Mean liposome diameter decreases with increasing inlet pressure, number of cycles and ethanol concentration, and increases raising ionic strength. No P concentration effect was observed. The variation of the entrapped volume of liposomes upon the cycles and pressure has a similar behavior to the diameter. Within the studied variable range, microfluidization does not increase the P oxidation index, nor does it significantly alter the P concentration.
Keywords: Experimental design; High-pressure homogenization; Liposome; Microfluidizer; Phospholipid; Statistical optimization;
In situ nasal absorption of midazolam in rats by J.-C Olivier; M Djilani; S Fahmy; W Couet (187-192).
Intranasal (i.n.) midazolam (MDZ) administrations may be used successfully for preoperative sedation, especially in young patients. However, clinicians have to use the commercial parenteral formulation, the low pH of which (3.3), necessary to solubilize MDZ (pK a 6.1), is probably responsible for the signs of local irritation frequently reported. As a starting point to design a formulation suitable for the nasal route, MDZ nasal absorption was investigated in rats. The effects of the MDZ solution concentration (10–100 μg/ml), osmolality (from less than 10 mOsm/kg up to 450 mOsm/kg) and pH (3.3–7.4) were studied using an in situ perfusion technique. MDZ was determined by reversed-phase HPLC in the circulating solution and results were expressed in clearance terms. MDZ absorption was independent of its concentration. The pH of the solutions was the key-parameter and only a pH above 4 allowed significant absorption. These results were consistent with a passive diffusion absorption of MDZ and partly followed the pH partition theory. In conclusion, satisfactory MDZ absorption should be expected with a formulation at a pH suitable for the nasal route in human (5.5–6.5).
Keywords: Intranasal administration; Midazolam; pH; Osmolality;
Simulation of skin permeability in chitosan membranes by H Dureja; A.K Tiwary; S Gupta (193-198).
To provide an alternative means of evaluating transdermal drug delivery systems, membranes of chitosan were developed. The membranes were prepared by cast-drying method. The effects of chitosan concentration, sodium tripolyphosphate (NaTPP) concentration and crosslinking (CL) time on flux and lag time were studied using central composite design. It was observed that chitosan membrane at a particular composition simulated the permeation of diclofenac sodium through rat skin The mathematical model developed in the present study can be used to simulate the permeation of drugs through different species of animal skins.
Keywords: Simulated skin; Chitosan membrane; Percutaneous permeation; Central composite design;
Evaluation of chemical stability of St. John's wort commercial extract and some preparations by Anna Rita Bilia; Maria Camilla Bergonzi; Fabrizio Morgenni; Giovanni Mazzi; Franco Francesco Vincieri (199-208).
Thermal and photostability of a commercial dried extract and capsules of St. John's wort (Hypericum perforatum L.) were evaluated under the ICH test conditions. The extract was considered as drug substance and its preparations as drug products. In addition, capsules of different colours corresponding to different opaficient and pigment contents were also evaluated as primary package of drug product and the tests in the secondary pack were performed with amber containers, as well. A selective high-performance liquid chromatography (HPLC) for determination of stability of all the characteristic constituents, namely flavonols, hyperforins and hypericins, was carried out. Photostability testing showed all the constituents to be photosensitive in the tested conditions. However, different opaficients and pigments present in the capsules influenced the stability of the different classes of constituents. Amber containers suggested as secondary packages influenced only in part the photostability of the investigated constituents. Long-term thermal stability testing showed a very low (less than 4 months) hyperforins and hypericins t90, even if ascorbic and citric acids were added to the formulation. From the results we have obtained it is clear that for St. John's wort preparations, a mere translation of the ICH guidelines to the field of herbal products, as suggested by the WPHMP of the EMEA, cannot be accepted. A revision and adaptation of the storage conditions should be elaborated.
Keywords: St. John's wort (Hypericum perforatum L.); Commercial extract and capsules; HPLC; Flavonols; Hyperforins and hypericins; Thermal and photostability;
The spray drying of acetazolamide as method to modify crystal properties and to improve compression behaviour by Piera Di Martino; Mara Scoppa; Etienne Joiris; Giovanni F Palmieri; Cyrille Andres; Yvette Pourcelot; Sante Martelli (209-221).
Acetazolamide shows a very poor compression ability and tablets must usually be produced through a wet granulation process. However, the possibility to obtain pure acetazolamide for direct compression could be interesting for industrial application. With the scope to obtain a material for direct compression, three different crystallisation methods were chosen, with respect to acetazolamide solvent solubility. (a) Acetazolamide was dissolved in an ammonia solution and then spray dried. It was possible to characterise the spherical particles as a mixture of two polymorphic forms, I and II by Powder X-ray diffraction study. (b) Pure form I was obtained by slowly cooling to room temperature a boiling water solution. (c) Pure form II, the marketed form, was obtained by neutralisation of an ammonia solution. Their compression behaviour was investigated firstly by a rotary press. Whilst pure polymorphic forms I and II could not be compressed, the spray dried particles showed very good compression properties. In fact, tablets were obtained only by spray dried particles, which show very good properties under compression and the absence of capping tendency. On the other hand, it was impossible to obtain tablets from polymorphic forms I and II, whatever compression pressures were used. In order to explain their densification mechanism, a single-punch tablet machine, equipped for the measurement of the upper punch displacement in the die, was used. From calculated Heckel's parameters, it was demonstrated that the spray dried material shows a greater particle rearrangement in the initial stage of compression due to its spherical habit and minor wrinkledness of particle surface. The crystalline structure due to the presence of polymorphic forms I and II concur to lowering the intrinsic elasticity of the material. This fact avoids the risk of the rupturing the interpaticulate bonds, which are formed during the compression, concurring to the consolidation of the tablet.
Keywords: Acetazolamide; Spray drying; Polymorphism; Compression behaviour; Densification behaviour;
Drug Stability, Principles and Practices, third edition, revised and expanded, Edited by J.T. Carstensen and C.T. Rhodes, in Drugs and the Pharmaceutical Sciences, Vol. 107, Marcel Dekker, New York, 2000, ISBN 0-8247-0376-6 by Gavin Halbert (223).