International Journal of Pharmaceutics (v.278, #1)
(EDI BOARD) (iii).
Poly-ϵ-caprolactone microspheres and nanospheres: an overview by V.R. Sinha; K. Bansal; R. Kaushik; R. Kumria; A. Trehan (1-23).
Poly-ε-caprolactone (PCL) is a biodegradable, biocompatible and semicrystalline polymer having a very low glass transition temperature. Due to its slow degradation, PCL is ideally suitable for long-term delivery extending over a period of more than one year. This has led to its application in the preparation of different delivery systems in the form of microspheres, nanospheres and implants. Various categories of drugs have been encapsulated in PCL for targeted drug delivery and for controlled drug release. Microspheres of PCL either alone or of PCL copolymers have been prepared to obtain the drug release characteristics. This article reviews the advancements made in PCL-based microspheres and nanospheres with special reference to the method of preparation of these and their suitability in developing effective delivery systems.
Keywords: Poly-ε-caprolactone; Microsphere; Implant;
Hemolysate-filled polyethyleneimine and polyurea microcapsules as potential red blood cell substitutes: effect of aqueous monomer type on properties of the prepared microcapsules by I El-Gibaly; M Anwar (25-40).
In this paper, we describe the synthesis and characterization of rabbit hemolysate-filled polyethyleneimine (PEI)- or polyurea (PU)-type artificial red blood cells (ARBCs) with different membrane compositions. These microcapsules were prepared by making use of the interfacial polymerization (IP) reaction between the water-soluble amine monomers (triethylamine (TEA), ethylene glycol-bis(β-aminoethyl ether)-N,N′-tetraacetic acid (EGATA), diethylenetriamine (DETA), tetramethyl diaminomethane (TMDAM), piperazine hexahydrate (PPHH), l-lysine monohydrochloride (LLMH) or PEI) and 2,4-toluylene diisocyanate (TDI) as an oil-soluble shell monomer. The resultant microcapsules were spherical and with mean diameters of 8.71–63.33 μm. Microcapsules having sulfonic acid groups on their surfaces were prepared by using a combination of the functional amines (DETA, LLMH or PEI) and 4,4′-diaminostilbene-2,2′-disulfonic acid (DASSA). Oxygen-binding abilities of the ARBCs were measured by a Clark-type oxygen electrode. The obtained results revealed that the highest oxygen-binding abilities were obtained with the PU-ARBCs prepared with DETA alone or in combination with EGATA. Unfortunately, these microcapsules exhibited large diameters and wider size distribution curves (span values (S)=1.3, 1.7, geometric standard deviation (σ g)=1.85, 2.18, respectively). However, the novel ARBCs (sulfonated PU-PEI graft copolymer membrane microcapsules (SPU/PEI-ARBCs)) prepared had good oxygen affinity, the smallest mean diameter (d=8.71 μm) and the best distribution (S=0.9, σ g=1.48) and a flow behavior identical to rabbit RBCs. Therefore, these unique microcapsules can be recommended for scale-up considerations as a promising blood substitute.
Keywords: Polyurea microcapsules; Interfacial polymerization; Hemoglobin microencapsulation; Polyethyleneimine membrane microcapsules;
Modification of physicochemical and mechanical properties of shellac by partial hydrolysis by Sontaya Limmatvapirat; Chutima Limmatvapirat; Manee Luangtana-anan; Jurairat Nunthanid; Toshio Oguchi; Yuichi Tozuka; Keiji Yamamoto; Satit Puttipipatkhachorn (41-49).
The shellac was modified by partial hydrolysis with 2.0% (w/w) NaOH for different times. The hydrolysed shellac was then evaluated for physicochemical and film properties in comparison with native shellac. The tablets coated with native and hydrolysed shellac were also evaluated. The results demonstrated that acid value (AV) of shellac increased with prolongation of hydrolysis time. The solubility of shellac in buffer solution (pH≤7) gradually increased with increasing hydrolysis time. The films prepared from hydrolysed shellac were more flexible and soft than those prepared from native shellac. The increasing of flexibility was correlated with the increasing of soft resin in shellac. The water vapor permeability of hydrolysed shellac film was lower than that of native shellac film. The higher acid permeability of the tablet coated with hydrolysed shellac was observed. In ethanol-based film coating, shellac had lower solubility and thus lower drug dissolution from coated tablets was observed. In ammonia-based film coating, the solubility of shellac was improved higher nearby pH 7.0 by an ammonium neutralisation method because of forming well-soluble salts, thereby higher drug dissolution was obtained. Partial hydrolysis provided modified shellac, which is more effective for ammonium salt formation, thus very higher drug dissolution was achieved in the ammonia-based coated tablets.
Keywords: Shellac; Enteric polymer; Coating; Films; Hydrolysis;
Acetaminophen-containing chewable tablets with suppressed bitterness and improved oral feeling by Hiroyuki Suzuki; Hiraku Onishi; Seiji Hisamatsu; Kosuke Masuda; Yuri Takahashi; Masanori Iwata; Yoshiharu Machida (51-61).
The aim of this study was to develop acetaminophen chewable tablets with suppressed bitterness and improved oral feeling by examination of hard fats as the matrix base and of sweetening agents as corrigents. Witepsol® H-15, W-35, S-55, E-75 and E-85, and Witocan® H and 42/44 were used as hard fats. Witocan® H and 42/44 were selected in view of improved oral feeling. Witocan® H/Witocan® 42/44 mixture tablets showed different melting characteristics and drug release rates dependent on their ratios, and those with the Witocan® H/Witocan® 42/44 ratio of 92.5% (w/w) and more showed good drug release. Sucrose, xylitol, saccharin, saccharin sodium, aspartame and sucralose were used as sweetening agents, and applied alone or with Benecoat BMI-40 or cocoa powder. The Witocan® H tablet with 1% (w/w) saccharin plus 5% (w/w) Benecoat BMI-40 (Sc1-B5), and the Witocan® H/Witocan® 42/44 (92.5:7.5, w/w) mixture tablet with 1% (w/w) aspartame plus 5% (w/w) Benecoat BMI-40 suppressed bitterness and sweetness excellently, but the former tablet showed better drug release. Thus, the Witocan® H tablet with Sc1-B5 is suggested as the best acetaminophen chewable tablet, exhibiting suppressed bitterness, low sweetness, improved oral feeling and good drug release.
Keywords: Acetaminophen chewable tablet; Hard fat; Bitterness; Sweetness; Oral feeling; Drug release;
Effect of β-sitosterol on the characteristics of vesicular gels containing chlorhexidine by E Farkas; R Schubert; R Zelkó (63-70).
Previous studies confirm that β-sitosterol is very effective in altering the molecular packing of soybean lecithin bilayers even more than the cholesterol. The primary aim of the present study was to evaluate the influence of the β-sitosterol portion in the lipid bilayer on the physical–chemical characteristics of the prepared gel systems, and its influence on the consequent drug release from the liposomes obtained from vesicular phospholipid gels (VPG-s) by redispersion. VPG-s were prepared of different molar ratios of lecithin:sterol components (10:90–35:65 mol%). The mixture was hydrated with the aqueous solution of chlorhexidin digluconate in order to achieve 30% (w/w) final concentration of the lipid mixtures and 4% (w/w) concentration of the drug in each homogenized VPG sample. To characterize the obtained VPG systems optical microscopic examinations using polarized light, differential scanning calorimetry (DSC), photon correlation spectroscopy (PCS), and dynamic surface tension measurements were carried out. Vertical type diffusion cell was applied to determine the amount of released chlorhexidine digluconate. As a result of the surface tension-decreasing effect of β-sitosterol, the membrane deformability and the dispersity of the system increased. The increased dispersity and fluidity significantly increased the extent of released chlorhexidine from the vesicles.
Keywords: Vesicular phospholipid gels (VPG); β-Sitosterol; Chlorhexidine digluconate release; Dynamic surface tension; Dispersity;
Development of a controlled release formulation based on SLN and NLC for topical clotrimazole delivery by E.B Souto; S.A Wissing; C.M Barbosa; R.H Müller (71-77).
Solid lipid nanoparticles (SLN) and nanostructured lipid carriers (NLC) are colloidal carrier systems providing controlled release profiles for many substances. Clotrimazole-loaded SLN and NLC were prepared by the hot high pressure homogenization technique in order to evaluate the physical stability of these particles, as well as the entrapment efficiency of this lipophilic drug and its in vitro release profile. The particle size was analyzed by PCS and LD showing that the particles remained in their colloidal state during 3 months of storage at 4, 20 and 40 °C. For all tested formulations the entrapment efficiency was higher than 50%. The obtained results also demonstrate the use of these lipid nanoparticles as modified release formulations for lipophilic drugs over a period of 10 h.
Keywords: Solid lipid nanoparticles; Nanostructured lipid carriers; Clotrimazole; Franz diffusion cells;
Influence of cryogenic grinding on properties of a self-emulsifying formulation by O Chambin; V Jannin; D Champion; C Chevalier; M.-H Rochat-Gonthier; Y Pourcelot (79-89).
Recently, self-emulsifying drug delivery systems (SEDDS) have been developed as a method to deliver lipophilic drugs. Gelucire® 44/14 is an excipient, from the lauroyl macrogolglycerides family, producing a fine oil-in-water emulsion when introduced into an aqueous phase under gentle agitation as SEDDS, improving thereby solubility of poorly water-soluble drugs and their bioavailability. The aims of this study were to process Gelucire® 44/14 into a powder by cryogenic grinding to produce solid oral dosage forms and to investigate influence of this process on different properties of a formulation made of Gelucire® 44/14 and ketoprofen (90/10). Cryogenic grinding produced Gelucire® 44/14 in a powder form and this process did not change its physical properties, emulsification capacities and dissolution performances of the formulation tested. However, interactions took place between ketoprofen and Gelucire® 44/14 with a decrease of the melting peak and a reduction of the droplet size of the formed emulsion. The influence of drug–Gelucire® 44/14 interactions must be investigated case by case in any formulations.
Keywords: Lipid formulations; Self-emulsifying systems; Gelucire® 44/14; Ketoprofen; Bioavailability; Cryogenic grinding;
Evaluation of new propofol aqueous solutions for intravenous anesthesia by Adriana Trapani; Valentino Laquintana; Angela Lopedota; Massimo Franco; Andrea Latrofa; Giuseppe Talani; Enrico Sanna; Giuseppe Trapani; Gaetano Liso (91-98).
The aim of this study was to evaluate the potential of using three new aqueous formulations of propofol for intravenous (i.v.) anesthesia. The first formulation can be prepared by using hydroxypropyl-γ-cyclodextrin (HP-γ-CD) as a solubilizer. Phase-solubility analysis showed a linear increase in the solubility of propofol to a maximum of 16.6 mg/ml in 30% (w/v) HP-γ-CD. Moreover, phase-solubility studies demonstrated that 18% (w/v) HP-β-CD or SBE-β-CD and 24% HP-γ-CD solutions, respectively, are required to dissolve 10 mg of propofol in 1 ml of the vehicle; the corresponding solutions, however, are slightly hypertonic. Autoclaving the 10 mg/ml CD-based formulations for 15 min at 121 °C caused a change in pH which was more evident for the HP-β-CD-based formulation while, in any case, no detectable fall in propofol concentration was observed. The second formulation herein evaluated is a co-solvent mixture (i.e., propylene glycol:water (1:1), v/v) which is able to dissolve 10 mg/ml of the anesthetic agent. However, although it is simple to prepare, the stability of this formulation is limited. The third aqueous formulation can be prepared by using the prolinate ester of propofol and its water-soluble derivative dissolved in water at equimolar concentration. The efficacy of all these formulations as i.v. anesthetic agents was assessed using a pharmacodynamic measure (onset and duration of loss of the righting reflex, LORR), and compared with that of the commercial propofol formulation (Diprivan®, 10 mg/ml) in rats. It was found that minimizing the amount of cyclodextrin in all CD-based formulations, anesthetic effects comparable to those of propofol in Diprivan® were still observed. Moreover, the prolinate ester constituted an effective i.v. anesthetic formulation with the same duration of action but with a longer induction time than Diprivan®.
Keywords: Propofol; Aqueous solutions; Intravenous anesthesia; Cyclodextrins; Prodrug;
Characterization and drug-permeation profiles of microporous and dense cellulose acetate membranes: influence of plasticizer and pore forming agent by Marcia M. Meier; Luiz A. Kanis; Valdir Soldi (99-110).
The use of pore forming agents and plasticizers are efficient ways to obtain membranes for controlled drug permeation through polymeric membranes. The challenge of the present study was to combine these two strategies to obtain cellulose acetate (CA) membranes, where poly(caprolactone triol) (PCL-T) was used as a plasticizer and water, dissolved in a casting solution, was used as a pore forming agent. First, the influence of water on membrane morphology, porosity and the permeation coefficient of a model drug (paracetamol) was analyzed. The influence of different amounts of PCL-T on the permeation coefficient of the CA membranes was then evaluated. Finally, both strategies were combined to obtain porous CA/PCL-T membranes. The membrane microstructure was analyzed using scanning electron microscopy (SEM), the CA crystallinity was determined via differential scanning calorimetry (DSC), and membrane permeability was investigated using paracetamol. The addition of water, a non-solvent, during the membrane casting process was found to be a simple and effective way to change membrane porosity and consequently the drug-permeation profile. When small quantities of non-solvent were used to obtain low porosity membranes, the presence of a plasticizer agent could be used to better modulate drug permeation. Combining the addition of PCL-T with the use of a non-solvent resulted in a series of CA membranes with paracetamol-permeation coefficient values in the range of ca. 10−7 to 10−5 cm s−1.
Keywords: Cellulose acetate; Poly(caprolactone triol); Plasticizer; Porous membrane; Drug permeation;
New hypoglycaemic agents selected by molecular topology by C. Calabuig; G.M. Antón-Fos; J. Gálvez; R. Garcı́a-Doménech (111-118).
New compounds showing hypoglycaemic activity have been designed through a computer aided method based on quantitative structure–activity relationship (QSAR) and molecular connectivity. After calculation of topological indices for a set of 89 compounds including active and inactive with regards to hypoglycaemic action, linear discriminant analysis was performed so that a useful model to predict such an activity was achieved. Later on, the discriminant model was applied on a huge database so that fourteen compounds were selected as potential new hypoglycaemics. From them, just five were finally selected for experimental test on expected hypoglycaemic activity. Among the selected compounds, l-arabitol, Acid blue 161, 1,4-butanediol diglycidil ether and Acid red 151 stand out, which are comparable in potency to standard drugs such as tolbutamide. Acid blue has a glycaemia profile similar to that of tolbutamide but does not lead to a severe hypoglycaemic condition, while the profile of the other agents is near normality.
Keywords: Molecular connectivity; Topological indices; Molecular topology; Linear discriminant analysis (LDA); Hypoglycaemic drugs;
Impact of excipients on the absorption of P-glycoprotein substrates in vitro and in vivo by Gilles Cornaire; John Woodley; Philippe Hermann; Alix Cloarec; Cécile Arellano; Georges Houin (119-131).
The efflux transporter, P-glycoprotein (P-gp), located in the apical membranes of intestinal absorptive cells, can reduce the bioavailability of a wide range of orally administered drugs. A number of surfactants/excipients have been shown to inhibit P-gp, and thus potentially enhance drug absorption. In this study, the improved everted gut sac technique was used to screen excipients for their ability to enhance the absorption of digoxin and celiprolol in vitro. The most effective excipients with digoxin were (at 0.5%, w/v): Labrasol > Imwitor 742 > Acconon E = Softigen 767 > Cremophor EL > Miglyol > Solutol HS 15 > Sucrose monolaurate > Polysorbate 20 > TPGS > Polysorbate 80. With celiprolol, Cremophor EL and Acconon E had no effect, but transport was enhanced by Softigen 767 > TPGS > Imwitor 742. In vivo, the excipients changed the pharmacokinetic profile of orally administered digoxin or celiprolol, but without increasing the overall AUC. The most consistent change was an early peak of absorption, probably due to the higher concentration of excipient in the proximal intestine where the expression of P-gp is lower. These studies show that many excipients/surfactants can modify the pharmacokinetics of orally administered drugs that are P-gp substrates.
Keywords: Digoxin; Celiprolol; Everted sacs; P-glycoprotein; Excipients; Surfactants;
In vitro evaluation of PLA nanoparticles containing a lipophilic drug in water-soluble or insoluble form by Eliana Leo; Barbara Brina; Flavio Forni; Maria Angela Vandelli (133-141).
Cloricromene (AD6), an anti-ischemic drug, is rapidly metabolised into a stable and active metabolite (cloricromene acid, AD6-acid) poorly soluble in water and less lipophilic than cloricromene. The aim of this study was to evaluate which of the two forms has more possibility to be efficiently encapsulated in nanoparticles based on poly(d,l-lactide) and prepared using the nanoprecipitation method. Increasing the theoretical loading of AD6, an increase in drug actual loading and in the mean particle size occurred, while no formation of nanoparticles was observed when the highest theoretical loading (50 mg) was employed. Changing the pH of the aqueous phase the drug content dramatically increased. However, at a pH value of 11 a more rapid hydrolysis of AD6 occurred. When AD6-acid was embedded in the nanoparticles, suitable results concerning both drug content and encapsulation efficiency were achieved. A good control in the release of AD6 from the AD6-loaded nanoparticles was observed while the liberation of AD6-acid from the AD6-acid-loaded nanoparticles was faster than the dissolution of the AD6-acid free. These results confirm that the most easy encapsulable form in nanoparticles is AD6-acid probably owing to its poor water solubility. Further studies will be carried out in order to evaluate if the increase in the liberation of AD6-acid by nanoencapsulation may have outcomes in its bioavaibility in vivo.
Keywords: Poly(d,l-lactide); Nanoparticles; Cloricromene; In vitro release;
A hydroxyethylated cholesterol-based cationic lipid for DNA delivery: effect of conditioning by A Percot; D Briane; R Coudert; P Reynier; N Bouchemal; N Lièvre; E Hantz; J.L Salzmann; A Cao (143-163).
We have synthesised a novel cholesterol-based cationic lipid to promote DNA transfer in cells. This lipid, dimethyl hydroxyethyl aminopropane carbamoyl cholesterol iodide (DMHAPC-Chol) contains a biodegradable carbamoyl linker and a hydroxyethyl group in the polar amino head moiety and is characterised by NMR. Liposomes prepared from this lipid and dioleoyl phosphatidyl ethanolamine (DOPE) in equimolar proportion showed a weak cytotoxicity as revealed by MTT assays and are efficient to deliver plasmids DNA evaluated by the expression of reporter genes in vitro and in vivo. In this paper, we present an original method to determine the lipid concentration based on the colorimetric detection of the colipid DOPE and the measure of the molar ratio DOPE/cationic lipid in the liposome by FTIR spectroscopy. The liposomes and lipid/DNA complexes structures were characterized by transmission electron microscopy (TEM) and by quasi-elastic light scattering (QLS). TEM indicated that the complexes correspond to aggregates containing globular substructures with liposomes size. The method of immuno-gold labelling was used to detect plasmid in the complex and reveals the presence of DNA inside the aggregates. Transfection results showed efficient DNA transfer depending on the charge ratio and liposomes conditioning. Gel retardation results indicated that at a molar charge ratio between X=1.5 and X=2.5 (depending on the liposome conditioning), all DNA was taken by liposomes. We showed that conditioning by freeze-drying (lyophilization) facilitates storage and improves transfection efficiency. When the liposomes were lyophilized prior to DNA addition or when the complexes were subjected to freeze-thawing cycles, the obtained complexes showed a transfection with levels enhanced up to four and five-fold respectively for the lyophilized liposomes and freeze-thawed complexes. NMR was used to characterize the modifications under freezing which showed an effect on 31 P spectra.
Keywords: Hydroxyethylated cationic lipid; Liposome characterization; Liposome conditioning; DNA delivery;
Milling of agglomerates in an impact mill by Joost J.A.M. Verheezen; Kees van der Voort Maarschalk; Fried Faassen; Herman Vromans (165-172).
Milling of agglomerates is one of the common unit operations during preparation of oral dosage forms like capsules and tablets. In literature the breakage of granules is mostly determined after single impact at an ideally formed granule or of single particles. In this paper the breakage behavior of agglomerates after milling with multiple impacts has been studied. It investigates the effects of the formulation and the influences of the mill settings. With respect to the formulation it has been found that both the size of the particles before granulation and the amount of binder used determine the breakage behavior. Both parameters have an influence on the strength of the granule to be milled, where initial particle size has the largest effect. A relation has been found between the strength of granules and the degree of size reduction. Regarding the mill settings, there are no mill parameters which influence the formation of fines independently. Formation of fines is always the result of the total degree of size reduction. It is not possible to achieve a large degree of size reduction without intensive fines formation. The results indicate that it is possible to achieve every desired average particle size. However, when formation of dust has to be reduced, multiple milling steps with separation of in-size particles is necessary.
Keywords: Agglomerates; Milling; Impact; Particle size; Size reduction;
Transdermal permeation of WIN 55,212-2 and CP 55,940 in human skin in vitro by Satyanarayana Valiveti; Paul K Kiptoo; Dana C Hammell; Audra L Stinchcomb (173-180).
Synthetic cannabinoids have a promising future as treatments for nausea, appetite modulation, pain, and many neurological disorders. Transdermal delivery is a convenient and desirable dosage form for these drugs and health conditions. The aim of the present study was to investigate the in vitro transdermal permeation of two synthetic cannabinoids, WIN 55,212-2 and CP 55,940. Transdermal flux, drug content in the skin, and lag times were measured in split-thickness human abdominal skin in flow-through diffusion cells with receiver solutions of 4% bovine serum albumin (BSA) or 0.5% Brij 98. Differential thermal analysis (DSC) was performed in order to determine heats of fusion, melting points, and relative thermodynamic activities. The in vitro diffusion studies in 0.5% Brij 98 indicated that WIN 55,212-2 diffuses across human skin faster than CP 55,940. The WIN 55,212-2 skin disposition concentration levels were also significantly higher than that of CP 55,940. Correspondingly, CP 55,940 was significantly metabolized in the skin. WIN 55,212-2 flux and skin disposition were significantly lower into 4% BSA than into 0.5% Brij 98 receiver solutions. There was no significant difference in the flux, lag time, and drug content in the skin of CP 55,940 in 4% BSA versus 0.5% Brij 98 receiver solutions. The DSC studies showed that CP 55,940 had a significantly lower melting point, smaller heat of fusion, and corresponding higher calculated thermodynamic activity than the more crystalline WIN 55,212-2 mesylate salt. The permeation results indicated that WIN 55,212-2 mesylate, CP 55,940, and other potent synthetic cannabinoids with these physicochemical properties could be ideal candidates for the development of a transdermal therapeutic system.
Keywords: WIN 55,212-2; CP 55,940; Transdermal delivery; Percutaneous absorption; Cannabinoids;
Surface studies on acrylic bone cement by A. Bettencourt; A. Calado; J. Amaral; A. Alfaia; F.M. Vale; J. Monteiro; M.F. Montemor; M.G.S. Ferreira; M. Castro (181-186).
Poly(methyl methacrylate) (PMMA) is used to fill the gap between the prosthesis and the surrounding bone in cemented arthroplasties. Biocompatibility problems related to bone cement application limit the clinical success of these cemented arthroplasties. Being the cement surface in close connection with the living bone, it is reasonable to assume that surface properties such as, surface composition and surface energy, will play a role in the biomaterial performance. X-ray photoelectron spectroscopy (XPS) analysis and surface energy studies were carried out during 4 months, in order to assess a possible correlation between aging time and surface changes. The aging of PMMA, in a biological model fluid, strongly influences the composition and wettability of the cement surface. These changes may be explained through the hydrolysis of PMMA ester groups and the subsequent hydrogen bonding. Although our study does not exactly reproduce the in vivo environment surrounding a prosthesis, it suggests that the changes in the composition and wettability of the surface may modulate the host response towards the implant, thus contributing to its loosening.
Keywords: Poly(methyl methacrylate); Methyl methacrylate; Bone cement; Aging; Surface chemistry; Surface energy;
A novel spray-drying technique to produce low density particles for pulmonary delivery by Hartwig Steckel; Heike G Brandes (187-195).
To date, all marketed DPI products rely on jet-milled, micronized drugs. Micronization often leads to drug powders exhibiting a large hydrophobic surface area resulting in strong cohesive forces, agglomeration and unsuitable aerosolization properties. In the current study, a new approach to prepare low density drug particles is described. Briefly, an oil-in-water emulsion consisting of an aqueous phase containing the dissolved model drug salbutamol sulphate, suitable surfactants, such as poloxamer or phosphatidylcholine, and optionally a bulking agent like lactose or a cyclodextrin derivative, and a lipid-phase that essentially consists of a liquefied propellant is spray-dried. By means of this process particles of very low density (0.02 g/cm3) and a drug load of 40% were prepared. The particle exhibit a porous to hollow structure, are thin-walled and of irregular shape. Depending on the composition of the aqueous phase, mean geometric particle sizes of <5 μm were obtained. It could be shown that a higher amount of poloxamer in the feed emulsion resulted in particles with improved dispersibility. Reducing the vapour pressure of the inner propellant phase by addition of dichloromethane decreased the agglomeration tendency of the powders as a result of the irregular particle morphology and, hence, resulted in higher fine particle fractions.
Keywords: Dry powder inhaler; Spray-drying; Fine particle fraction; Efficiency; Phosphatidylcholine; Dipalmitoylphosphatidylcholine; Emulsion-spray technique;
Instructions to authors (201-206).