European Journal of Pharmaceutics and Biopharmaceutics (v.67, #3)
Effect of excipients on the encapsulation efficiency and release of human growth hormone from dextran microspheres
by K.D.F. Vlugt-Wensink; Y.J. Meijer; M.J. van Steenbergen; R. Verrijk; W. Jiskoot; D.J.A. Crommelin; W.E. Hennink (pp. 589-596).
The possibility was investigated to modulate the encapsulation efficiency and release of human growth hormone (hGH) from hydroxyl ethyl methacrylated dextran (dex-HEMA) hydrogel microspheres by using excipients. Microspheres were prepared by polymerization of dex-HEMA in an aqueous two-phase system of this polymer and PEG with or without excipients (Tween 80, pluronic F68, sucrose, NaCl, urea or methionine). High hGH encapsulation efficiencies (50–70%) were obtained for microspheres prepared without excipients and with Tween 80, NaCl or methionine. Substantially lower encapsulation efficiencies (27% and 19%, respectively) were obtained for microspheres prepared in the presence of sucrose and urea, which was attributed to the more favoured partitioning of hGH over the PEG-phase due to higher hydrophobicity of the (partly) denatured hGH. Likely, differences in precipitate size of the encapsulated hGH resulted in different release profiles between microspheres prepared without excipients (biphasic release: 2 days delay time followed by 6 days release) and the release profile for microspheres prepared with Tween 80, pluronic F68, sucrose, NaCl and urea (release over a period of 6–8 days (without a delay time)). Microspheres prepared with methionine showed a concentration-dependent delay time varying from 0 to 2 days followed by almost zero-order release over 6 days, attributed to the effect of methionine on the polymerization of dex-HEMA. Especially, Tween 80 and methionine are attractive excipients since hGH was encapsulated in high yield (60–70%) and the protein was released from the microspheres mainly in its monomeric form without a delay time and with an almost zero-order release over 6–8 days.
Keywords: dex-HEMA microspheres; hGH; Excipients; Hydrogel; Protein release; Microspheres
Preparation and characterization of radioactive dirhenium decacarbonyl-loaded PLLA nanoparticles for radionuclide intra-tumoral therapy
by Misara Hamoudeh; Hani Salim; Dumitru Barbos; Coustantin Paunoiu; Hatem Fessi (pp. 597-611).
This study describes the development of biocompatible radioactive rhenium-loaded nanoparticles for radionuclide anti-cancer therapy. To achieve this goal, dirhenium decacarbonyl [Re2(CO)10] has been encapsulated in poly(l-lactide) based nanoparticles by an oil-in-water emulsion–solvent evaporation method. A 33 factorial design method was applied to investigate the influence of both the proceeding and formulation parameters including the stirring speed and the concentration of both the PLLA polymer and the poly(vinyl alcohol) stabiliser on both nanoparticles size and the Re2(CO)10 encapsulation efficacy. The factorial design results attributed a clear negative effect for the stirring speed and the stabiliser concentration on the nanoparticles size while the polymer concentration exhibited a positive one. Regarding the Re2(CO)10 encapsulation efficacy, higher values were obtained when higher polymer concentrations, lower stabiliser concentrations or slower stirring speeds were applied in the preparation. Different tests were thereafter performed to characterize the Re2(CO)10-loaded nanoparticles. The nanoparticles size, being experimentally controlled by the above mentioned parameters, ranged between 330 and 1500nm and the maximum rhenium loading was 24% by nanoparticles weight as determined by atomic emission assays and neutron activation analysis. Furthermore, the rhenium distribution within nanoparticles has been shown to be homogeneous as confirmed by the energy dispersive X-ray spectrometry. DSC assays demonstrated that Re2(CO)10 was encapsulated in its crystalline initial state. Other experiments including FT-IR and NMR did not show interactions between PLLA and Re2(CO)10. To render them radioactive, these nanoparticles have been bombarded with a neutron flux of 1.45×1013n/cm2/s during 1h. The SEM micrographs of nanoparticles after neutron bombardment showed that the nanoparticles remained spherical and separated but slightly misshaped. These applied neutron activation conditions yielded a specific activity of about 32.5GBq per gram of nanoparticles. Preliminary estimations allow us to think that a sole injection of 50mg of these activated nanoparticles into a brain tumor model (4.2cmdiameter) would deliver a tumor absorbed dose of up to 47Gy. In conclusion, these dirhenium decacarbonyl-loaded nanoparticles represent a novel promising tool for radionuclide anti-cancer therapy.
Keywords: Rhenium; Dirhenium decacarbonyl; Radioactivity; PLLA; Nanoparticles; Radionuclide; Encapsulation; Cancer
Influence of preparation conditions and heat treatment on the properties of supercooled smectic cholesteryl myristate nanoparticles
by J. Kuntsche; H. Bunjes (pp. 612-620).
Colloidal dispersions of cholesterol esters in the supercooled smectic state are under investigation as a novel drug carrier system in particular with respect to parenteral application. In the present study, suitable conditions for the homogenization of cholesteryl myristate dispersions stabilized with a phospholipid/bile salt blend were evaluated. For effective particle size reduction homogenization with high pressure and at temperatures above the melting temperature of the cholesterol ester (isotropic melt) is necessary. Homogenization at lower temperature where the matrix lipid is in the smectic state is less effective even when applying the highest homogenization pressure possible but still leads to dispersions with particles in the colloidal size range.Since sterility is required for parenteral medications and is usually achieved by autoclaving for aqueous systems, the physical and chemical stability of cholesteryl myristate nanoparticles stabilized with different surface active agents during heat treatment was investigated as well. The dispersions were characterized by particle size and zeta potential measurements, differential scanning calorimetry (DSC) and high performance thin layer chromatography (HPTLC). The results indicate that cholesteryl myristate nanoparticles stabilized with phospholipid/sodium glycocholate, polyvinyl alcohol, poloxamer and poloxamine can be sterilized by autoclaving. Compared to cholesterol ester free dispersions of phospholipids, the phospholipid seems to be more stable against hydrolysis during prolonged heat treatment in the phospholipid/bile salt containing cholesteryl myristate dispersions.
Keywords: Lipid nanoparticles; Supercooled smectic nanoparticles; Homogenization; Autoclaving; Stability; Cholesterol esters
Nanoparticles based on the complex of chitosan and polyaspartic acid sodium salt: Preparation, characterization and the use for 5-fluorouracil delivery
by Yongli Zheng; Wuli Yang; Changchun Wang; Jianhua Hu; Shoukuan Fu; Ling Dong; Lili Wu; Xizhong Shen (pp. 621-631).
New nonstoichiometric polyelectrolyte complex nanoparticles were prepared based on chitosan (CS) and polyaspartic acid sodium salt (PAsp). The physicochemical properties of the complexes were investigated by means of turbidity, dynamic light scattering, transmission electron microscopy and zeta potential. The results indicated that the slow dropwise addition of chitosan into PAsp allowed to elaborate either anionic or cationic particles in the size range of 85–300nm with proper CS and PAsp unit molar ratios. Investigation of structural changes during the addition of CS revealed that the microstructure of the nanoparticles depended strongly on the unit molar ratio of CS to PAsp. Nanoparticles containing a hydrophilic drug, 5-fluorouracil (5FU), were prepared by mixing and absorption method. In vitro and in vivo experiment indicated that the drug-loaded CS–PAsp nanoparticles presented a sustained release of 5FU compared to the 5FU solution and the areas under curve (AUC) were increased by about four times.
Keywords: Chitosan; Polyaspartic acid; Nanoparticle; Controlled drug release; 5-Fluorouracil
Oral low molecular weight heparin delivery by microparticles from complex coacervation
by Alf Lamprecht; Nathalie Ubrich; Philippe Maincent (pp. 632-638).
As low molecular weight heparins exhibit limited oral absorption they usually have to be administered parenterally. Their strong negative charge appears to be one of the biggest hurdles to overcome in order to increase oral absorption. Complex coacervation has been proposed as a microencapsulation technique for increased oral drug absorption on the basis of charge compensation. Optimized tinzaparin/acacia gum mixture were coacervated with either gelatin A or B leading to microparticles with monodispersed size distribution, good fluidity and high encapsulation rates (>90%), while mean particle size varied between 5 and 20μm, respectively, depending on the gelatin type. Tinzaparin was homogeneously distributed throughout the particle matrix and anti-Xa activity was maintained during preparation and storage. Drug release occurred in dependency of the pH triggering the dissociation between tinzaparin/acacia and gelatin. Cell binding experiments on Caco-2 led to slightly increased adhesion of gelatin A microparticles compared to gelatin B (A: 3.5±0.3%; B: 2.5±0.3%; solution: 1.9±0.1%), while drug transport did not differ from free tinzaparin solution. In-vivo results demonstrated an oral bioavailability of about 4.2±2.9% with gelatin B particles while gelatin A led to no absorption of tinzaparin. In conclusion, tinzaparin microparticles exhibited excellent particle properties in vitro and demonstrate potential for a formulation increasing the oral bioavailability of low molecular weight heparins.
Keywords: Microparticles; Complex coacervation; Low molecular weight heparin; Tinzaparin; Oral absorption; Gelatin
Targeted transfollicular delivery of artocarpin extract from Artocarpus incisus by means of microparticles
by Tasana Pitaksuteepong; Atawit Somsiri; Neti Waranuch (pp. 639-645).
Artocarpin (Ar), an extract of heartwood of Artocarpus incisus, possesses potent 5α reductase inhibitory effect. The penetration of Ar into the deeper layers of the skin where androgen receptors are present is limited. Therefore, this study was aimed to prepare alginate/chitosan (ACS) microparticles for targeted transfollicular delivery. It was found that a suitable particle size ranging from 2 to 6μm can be prepared using the ionotropic gelation technique. Entrapment efficiency of Ar in ACS microparticles was 18.7±1.7%. The release of Ar from the ACS microparticles over 6h was 0.7% of the loading dose suitable for a long-term release of Ar in the follicular ducts. The optimal growth suppression of the hamster flank organs could be achieved by topical application of Ar-ACS microparticles with a content of 0.1mg in 5mg microparticles to one hamster flank while the other flank (intraspecies control) showed the normal growth of the flank organs and Ar at the same concentration in solution form could not suppress the growth of the flank organs to the same extent. The efficiency of Ar 0.1mg loaded in ACS microparticles was shown to be comparable to a dose of 1mg Ar applied as solution. However, Ar formulated in microparticles did not show significant systemic action compared to the dermal application of an Ar solution and a flutamide preparation (1mg) as positive control.
Keywords: Alginate; Chitosan; Microparticles; Artocarpin; Artocarpus incisus; 5α-Reductase inhibitor; Targeted follicular delivery; Pigmented macules
MMPs-specific PEGylated peptide–DOX conjugate micelles that can contain free doxorubicin
by Gee Young Lee; Kyeongsoon Park; Sang Yoon Kim; Youngro Byun (pp. 646-654).
The goal of this study was to develop anti-cancer drug conjugates with increased anti-tumor effect and reduced toxicity. In this regard, we utilized the physiological characteristics of tumors such as angiogenesis, the expression of matrix metalloproteinases (MMPs) and the enhanced permeability and retention (EPR) effect, and designed MMPs-specific PEGylated peptide–DOX conjugate micelles containing doxorubicin. These conjugates were prepared by using two peptides, GPLGV and GPLGVRG (P5D and P7D, respectively), and doxorubicin was loaded into micelles formed by each conjugate. P5D and P7D were specifically cleaved by active MMP-2 and all conjugates showed significantly better cell viability than doxorubicin at equivalent concentrations. In vivo, animals treated with PEGylated peptide–DOX conjugate micelles showed approximately 50% of the tumor growth of the control, and doxorubicin-loaded conjugates micelles inhibited tumor growth up to about 72% compared with the control, which matched the effect of doxorubicin. Doxorubicin-loaded PEGylated peptide–DOX conjugate micelles exhibited longer half-lives and maintained higher concentrations of doxorubicin in plasma than PEGylated peptide–DOX conjugate micelles alone. Doxorubicin-loaded PEGylated peptide–DOX conjugate micelles might offer a cancer therapy with an activity that is similar to that of the parent drug but with reduced toxicity.
Keywords: Abbreviations; MMPs; matrix metalloproteinases; DOX; doxorubicin; IC; 50; 50% inhibitory concentration; MTD; maximum tolerance dose; LD; 50; 50% lethal doseMatrix metalloproteinases (MMPs); Conjugate micelles; PEGylated peptide; Doxorubicin loading; Cancer therapy
Liposomes for drug delivery to the lungs by nebulization
by Marco Zaru; Spyridon Mourtas; Pavlos Klepetsanis; Anna Maria Fadda; Sophia G. Antimisiaris (pp. 655-666).
Preparation of drug-loaded freeze-dried (FD) liposomes, designed for delivery to lungs after rehydration/nebulization was investigated. Rifampicin (RIF) incorporating multilamelar (MLV) and dried rehydrated vesicles (DRV); composed of phosphatidylcholine (PC), dipalmitoyloglycero-PC (DPPC) or distearoyloglycero-PC (DSPC), containing or not Cholesterol (Chol), were prepared. Vesicles were characterized for encapsulation efficiency (EE%), size distribution, zeta-potential, stability during freeze drying (FD) and nebulization (nebulization efficiency (NE%) and retention of RIF after nebulization (NER%)). Mucoadhesion and toxicity in A549 cells was measured. RIF EE% was not affected by liposome type but lipid composition was important; Synthetic lipid vesicles (DPPC and DSPC) had higher EE% compared to PC. As Chol increased EE% decreased. Freeze drying (FD) had no effect on EE%, however trehalose decreased EE% possibly due to RIF displacement. NER% was highly affected by lipid composition. Results of NE% and NER% for RIF-loaded liposomes show that DSPC/Chol (2:1) is the best composition for RIF delivery in vesicular form to lungs, by nebulization. Mucoadhesion and A549 cell toxicity studies were in line with this conclusion, however if mucoadhesion is required, improvement may be needed.
Keywords: Liposome; Lipid composition; Microparticle; Alveolar delivery; Lungs; Rifampicin; Nebulization; Aerosol; Amphiphilic drug; Mucoadhesion
Dry powder inhalation of hemin to induce heme oxygenase expression in the lung
by G.S. Zijlstra; C.A. Brandsma; M.F.H. Harpe; G.M. Van Dam; D.J. Slebos; H.A.M. Kerstjens; A.H. De Boer; H.W. Frijlink (pp. 667-675).
The purpose of this study was to formulate hemin as a powder for inhalation and to show proof of concept of heme oxygenase 1 (HO-1) expression in the lungs of mice by inhalation of hemin. Hemin was spray dried from a neutralized sodium hydroxide solution. The particle size distribution of the powder was between 1 and 5μm. Dispersion from the Twincer dry powder inhaler showed a fine particle fraction (<5μm) of 36%. A specially designed aerosol box based on the Twincer®-inhaler was used for a proof of concept study of HO-1 induction by inhalation of hemin in mice. The aerosol in the exposure chamber of the aerosol box remained aerosolized up to 5min. A rhodamin B containing aerosol was used to show that the aerosol box gave deposition over the entire lung indicating the suitability of the model. Additionally, inhalation of hemin showed a dose dependent increase in HO-1 protein expression in the lungs. In conclusion, hemin was successfully formulated as a powder for inhalation and the inhalation model allowed controlled HO-1 expression in the lungs of mice. Future studies investigating the utility of inhaled hemin in treating disease states are warranted.
Keywords: Heme oxygenase; Hemin; Dry powder inhalation; Mice; Spray drying; Fluorescent imaging
Antitumor effect of an injectable in-situ forming drug delivery system composed of a novel tissue adhesive containing doxorubicin hydrochloride
by Sachiro Kakinoki; Tetsushi Taguchi (pp. 676-681).
Our group has developed a novel tissue adhesive composed of biomacromolecules and organic acid derivatives which have good biocompatibility and exhibit high bonding strength to living tissues. We propose to use this tissue adhesive for in-situ forming drug delivery system (DDS) for cancer chemotherapy. In a previous work, we had prepared a novel in-situ forming DDS composed of human serum albumin (HSA) and tartaric acid derivative (TAD) containing doxorubicin hydrochloride (DOX), and we had demonstrated an in vitro release profile of DOX from HSA–TAD gel for approximately up to 100h. Here, we report on antitumor effect of this injectable in-situ forming DDS. Local injection of DOX by the HSA–TAD was administered to human colon carcinoma (WiDr) implanted subcutaneously onto the immunodeficient mouse. The results of the in vivo experiments showed that the presence of DOX in blood of mice was detectable for up to 3days, and that the tumor volume was effectively minimized with injection of HSA–TAD containing DOX. The in-situ forming DDS with the novel tissue adhesive containing DOX, therefore, is a useful technique for cancer chemotherapy.
Keywords: Tissue adhesive; Hydrogel; Drug delivery system; Human serum albumin; Tartaric acid; Injectable; in-situ forming; N; -Hydroxysuccinimide; Doxorubicin; Antitumor effect
Physical gels of a carboxymethyl derivative of scleroglucan: Synthesis and characterization
by Maria Antonietta Casadei; Pietro Matricardi; Giancarlo Fabrizi; Michelle Feeney; Patrizia Paolicelli (pp. 682-689).
A carboxymethyl derivative of scleroglucan (Scl-CM) was synthesized and characterized through FT-IR,1H NMR and potentiometer titration. Rheological studies allowed evidencing the effect produced by the introduction of the carboxymethyl moiety on the native polymer. The mechanical spectrum of the scleroglucan solution showed a weak gel behaviour, while the derivative one looked like a system near the gel point, that evolved to a gel state depending on the concentration. This difference could be related to conformational changes due to the introduction of the negative charges on the chains. Different concentrations of Ca2+, added to the aqueous solutions of Scl-CM, were able to deeply modify the resulting system, showing a sharp transition toward a gel like behaviour. Acyclovir was loaded into the hydrogels obtained with different amounts of polymer and salt. The release rate of the drug from these systems was strictly related to both concentrations of salt and polymer. The obtained results suggest a possible employment of these new hydrogels for topical formulations or in situ implantation.
Keywords: Carboxymethyl scleroglucan; Physical hydrogels; Rheology; Acyclovir; Controlled release
Enhanced enteric properties and stability of shellac films through composite salts formation
by Sontaya Limmatvapirat; Chutima Limmatvapirat; Satit Puttipipatkhachorn; Jurairat Nuntanid; Manee Luangtana-anan (pp. 690-698).
The objective of this study was to improve the properties of shellac by composite salts formation. The shellac samples were prepared in various salt forms by dissolving them with 2-amino-2-methyl-1-propanol (AMP) and ammonium hydroxide (AMN) at various ratios of AMP:AMN. The results demonstrated that aqueous solubility of the shellac salts was improved as the ratio of AMP:AMN increased. The absorbance ratio of the FTIR peaks assigned to CO stretching of carboxylate and carboxylic acid (ABS1556/ABS1716) was increased with the increase of the AMP fraction, suggesting that the solubility enhancement was due to more ionization of AMP salts. Moisture adsorption studies indicated that shellac salts were more hygroscopic as AMP content increased. After storage at 40°C, 75% RH, the acid value and insoluble solid of AMP salts were relatively constant even after storage of up to 180 days, suggesting that AMP should protect polymerization. The ABS1556/ABS1716 values of the shellac salts were rapidly decreased after storage, especially for those consisting of a high percentage of AMN. Thus, AMP should bind much tighter at the carboxylate binding site as compared with AMN, resulting in more solubility and stability. In conclusion, optimized shellac properties could be easily accomplished by composite salts formation.
Keywords: Shellac; Salt; Enteric; Film; Stability; Ammonia; 2-Amino-2-methyl-1-propanol
Comparison of stratum corneum penetration and localization of a lipophilic model drug applied in an o/w microemulsion and an amphiphilic cream
by Alexa Teichmann; Sandra Heuschkel; Ute Jacobi; Gaëlle Presse; Reinhard H.H. Neubert; Wolfram Sterry; Jürgen Lademann (pp. 699-706).
Vehicle dependent effects on the penetration behavior of drugs following topical application are well known from the literature. In this context, many reports concerning the enhancing activities for hydrophilic as well as lipophilic substances by colloidal drug carrier systems, particularly microemulsions, are available. However, there is little knowledge about the localization of the drugs within the skin and the stratum corneum, respectively. In the present study, the lipophilic dye curcumin incorporated in an oil-in-water microemulsion and in an amphiphilic cream was applied onto the skin of human volunteers. Using the method of tape stripping to remove the stratum corneum (SC), the depth profiles of the dye within the horny layer were compared. Applying the microemulsion, a deeper part of the SC was accessible by a number of 20 tapes removed and significantly smaller amounts of curcumin were found on the skin surface. Also differences in the distribution and localization of the dye within the stratum corneum were observed by laser scanning microscopy. Furthermore, curcumin was detected in hair follicles. It was obvious that the microemulsion led to a penetration into the complete follicular infundibula, whereas, following application of the cream, a fluorescence signal was only received from the follicular orifices.
Keywords: Microemulsion; Penetration; Curcumin; Tape stripping; Stratum corneum; Follicle
Biphasic release of indomethacin from HPMC/pectin/calcium matrix tablet: I. Characterization and mechanistic study
by Baojian Wu; Zhukang Chen; Xiuli Wei; Ningyun Sun; Yi Lu; Wei Wu (pp. 707-714).
Calcium-induced crosslinking of pectin acts as the dominating factor controlling drug release from pectin-based matrices. The same interaction was employed to modify indomethacin release from HPMC/pectin/calcium matrix in this study. The aim was to characterize the release profiles, and to study the formulation variables and the underlying mechanisms. The matrix tablet was made up of pectin HM 70, calcium chloride and HPMC K4M, and prepared by the wet granulation method. In vitro release was performed in water and characterized by the power law. Matrix erosion was evaluated by studying the weight loss and pectin release. Biphasic release of indomethacin from the HPMC/pectin/calcium matrix tablet was observed, and extraordinary power law exponent n values of over 1.0 were observed. Increase in calcium amount led to more significant retardation on drug release. The two power law parameters, n and K, correlated to the amount of calcium in the matrix. A lag time of over 4h can be achieved at HPMC/pectin/calcium chloride amount of 100mg/100mg/100mg. Both matrix weight loss and pectin release were linearly correlated to indomethacin release, indicating erosion-controlled drug release mechanisms. The hybrid matrix showed retarded erosion and hydration rate, which served as the basis for retarded indomethacin release. It is concluded that the pectin/calcium interaction can be employed to modify drug release from HPMC/pectin/calcium matrix tablet with biphasic release patterns for potential timed or site-specific drug delivery.
Keywords: Pectin; HPMC; Calcium ions; Matrix; In situ crosslinking; Biphasic release
Immediate release of poorly soluble drugs from starch-based pellets prepared via extrusion/spheronisation
by Aleksandra Dukić-Ott; Jean Paul Remon; Paul Foreman; Chris Vervaet (pp. 715-724).
The aim of this study was to evaluate modified starch (high-amylose, crystalline and resistant starch) as the main excipient for immediate-release pellets containing poorly soluble drugs (hydrochlorothiazide and piroxicam) and prepared via extrusion/spheronisation. The bioavailability of pellets (containing 50mg hydrochlorothiazide) was determined after oral administration to 6 dogs. A 24-factorial design with central point was used to evaluate the influence of hydrochlorothiazide (10% and 50%, w/w), HPMC (binder, 4% and 7%, w/w), sorbitol (0% and 10%, w/w) and water (granulation liquid, low and high level) on pellet yield, size (Feret mean diameter) and sphericity (aspect ratio and two-dimensional shape factor, eR). Optimal granulation liquid content depended on drug and sorbitol level in the formulation. All factors except sorbitol content, as well as the interactions between drug concentration and binder level and between drug and water level, were significant ( P<0.05) for pellet yield, while a significant curvature ( P<0.05) suggested non-linearity of the response plots. The model was not significant for pellet shape, while hydrochlorothiazide and water level as well as their interaction were significant ( P<0.05) for pellet size. Pellet friability, disintegration, residual water content and in-vitro drug release were determined. Pellets containing 2.5% (w/w) piroxicam were also evaluated. For both model drugs, pellets with a high yield (>90%), acceptable sphericity (AR<1.2) and low friability (<0.01%) were obtained. Due to pellet disintegration, fast dissolution of both hydrochlorothiazide and piroxicam was achieved: >80% drug released in 30min. The bioavailability (AUC0→24h, Cmax and tmax) of hydrochlorothiazide pellets in dogs was not significantly different from fast-disintegrating immediate-release hydrochlorothiazide tablets ( P>0.05).
Keywords: Extrusion/spheronisation; Pellets; Starch; Hydrochlorothiazide; Piroxicam; In-vivo; evaluation
Effect of formulation parameters on the release characteristics of propranolol from asymmetric membrane coated tablets
by Amit Garg; Mukur Gupta; H.N. Bhargava (pp. 725-731).
Controlled delivery of drugs has been achieved successfully by use of asymmetric membranes. In our study, we have evaluated the influence of various preparation parameters such as concentration of the polymer, concentration of the pore former and temperature of the precipitation bath on the permeability and the release characteristics of propranolol. Propranolol tablets were prepared by direct compression and were coated with varying concentrations of cellulose acetate and glycerin. The coat was precipitated in water, maintained at various temperatures, followed by air drying of the coat. Scanning Electron Microscopy (SEM) was used to characterize the asymmetric structure of the membrane. The influence of various preparation parameters on the release of propranolol from asymmetric coated tablets was evaluated. SEM confirmed the asymmetric nature of the membrane. A zero order release of propranolol was obtained from the coated tablets of propranolol. Various preparation parameters studied significantly affected ( p<0.05) the release of propranolol hydrochloride from the asymmetric membrane coated tablets and the release was independent of the pH and the rate of agitation of the dissolution medium ( p>0.05). Asymmetric membranes can be successfully utilized in the controlled delivery of highly water soluble drugs like propranolol and by modifying preparation parameters like polymer concentration, pore former concentration and temperature of the precipitation bath, desired release rates can be obtained.
Keywords: Propranolol hydrochloride; Asymmetric membrane; Osmosis; Osmotic drug delivery system; Controlled porosity membranes; Cellulose acetate
Enhancement of the dissolution of indomethacin in interactive mixtures using added fine lactose
by Ayman Allahham; Peter J. Stewart (pp. 732-742).
The objective of the study was to investigate the effect of fine lactose on the in vitro dissolution of indomethacin in interactive mixtures containing spray-dried lactose and lactose monohydrate (106–250μm). Dissolution of the indomethacin was measured using an automated dissolution apparatus following the USP paddle method at 100rpm. The particle size distributions of indomethacin mixtures were measured using a Mastersizer S under non-sink conditions. Data fitted bi-exponential or tri-exponential dissolution models, representing dissolution from dispersed and agglomerated particle distributions. The addition of fine lactose (VMD 3.8±0.4μm) to 20% indomethacin-coarse lactose mixtures resulted in significantly increased rates of dissolution caused by increases in the estimated dissolution rate constants for dispersed particles ( Kd) and by de-agglomeration. Agglomerates in the mixture showed little tendency to comminute under shear pressure. De-agglomeration in the dissolution medium was attributed to increased porosity of agglomerates, caused by dissolution of water soluble fine lactose in the agglomerate structure. The median particle size ( D50) of the dispersed particle distribution decreased with increasing concentrations of added fine lactose, indicating increasing extents of de-agglomeration, and a good correlation between Kd and ( D50)2 resulted for the coarse lactose-based mixtures ( R2>0.984).
Keywords: Indomethacin interactive mixtures; In vitro; dissolution; De-agglomeration; Poorly water-soluble drugs; Particle sizing; Mathematical models; Oral drug delivery; Milling and solid dosage form
Thermochemical analysis of the dissolution process of Griseofulvin
by J. Knoblauch; I. Zimmermann (pp. 743-751).
Very often poor water solubility limits the therapeutic use of drug molecules. In order to develop strategies to overcome this handicap a basic understanding of this phenomenon is needed. In this paper Griseofulvin is used as a model substance. According to the Hess theorem the direct dissolution of Griseofulvin is replaced by a series of alternative processes which in their combination have the same starting point as well as the same endpoint as the direct dissolution. The energies associated with these alternative processes however can be determined more exactly than the dissolution energy. In cases where the measurement of an energy is impossible, e.g. the transfer energy of single molecules from the vapor phase into water, this energy is calculated by quantum chemical methods. In addition these alternative processes allow for a better understanding of the elementary steps involved in the dissolution process. The energies determined for the various alternative processes are compared with the dissolution energies as calculated by means of AMSOL. An excellent agreement can be observed.
Keywords: Griseofulvin; Energy; Thermochemical analysis; AMSOL; Solvation; Sublimation; Dissolution; Hess theorem
Proline prodrug of melphalan, prophalan-l, demonstrates high therapeutic index in a murine melanoma model
by Sachin Mittal; Yasuhiro Tsume; Christopher P. Landowski; Kyung-Dall Lee; John M. Hilfinger; Gordon L. Amidon (pp. 752-758).
The therapeutic efficacy of prophalan-l, thel-proline prodrug of melphalan that demonstrated prolidase-dependent bioactivation to melphalan, was examined in vivo in a mouse melanoma model. Prophalan-l exhibited 2- to 2.5-fold higher hydrolytic and cytotoxic activity than prophalan-d, thed-analog, in B16-F10 murine melanoma cells in vitro. Prophalan-l cytotoxicity in B16-F10 cells was lower (GI50=221μM) than that of melphalan (GI50=173μM). The tumor growth profiles in C57BL/6J mice injected with B16-F10 cells and treated with melphalan (5.5μg/g i.p.) and equimolar concentrations of the prodrugs demonstrated significant difference between the control (buffered saline) and melphalan or prophalan-l but no significant difference between control and prophalan-d or between melphalan and prophalan-l. Prophalan-l was significantly less toxic than melphalan, while no significant difference was observed in toxicity, measured as percent weight loss, between the prodrugs and saline control. Tumor reduction efficacy at high doses (12μg/g i.p.) was similar for melphalan and prophalan-l; however, fatal toxicity was associated with melphalan while prophalan-l exhibited significantly lower systemic toxicity. An excellent correlation between GI50 and tumor reduction efficacy was observed for the tested drugs ( r2=0.95). Prophalan-l thus demonstrates higher therapeutic index than melphalan in the murine melanoma model.
Keywords: Prodrug; Melphalan; Mouse melanoma model; Prolidase; Therapeutic efficacy
The role of the lymphatic system in subcutaneous absorption of macromolecules in the rat model
by Leonid Kagan; Pavel Gershkovich; Avivit Mendelman; Sofia Amsili; Nathan Ezov; Amnon Hoffman (pp. 759-765).
The purpose of this study was to assess the contribution of lymphatics to the systemic bioavailability of macromolecules following SC administration in a rat model. The rat model included continuous lymph collection from the thoracic lymph duct and concurrent serial blood sampling from freely moving animals. A thoracic lymph duct – jugular vein shunt produced by an implanted connective cannula, and maintained during the recovery period, enabled superior rat survival and prevented lymphatic cannula occlusion. The SC absorption of three macromolecules (bovine insulin, bovine serum albumin, and recombinant human erythropoietin alpha) was assessed in comparison to the non-lymph cannulated control group. For all tested molecules, only minimal amounts (less than 3%) of the SC administered dose were detected in the collected lymph. In the rat model, following SC administration, the macromolecules were absorbed mainly through the blood capillaries with minimal contribution of the lymphatic system to systemic bioavailability. The relatively small elevation in the lymphatic concentration, which occurred in all molecules, may be attributed to the redistribution of the molecules from the blood to the interstitial fluid compartment. These findings are important since rodents are commonly used in preclinical evaluation of macromolecular drugs.
Keywords: Pharmacokinetics; Lymphatic uptake; Therapeutic protein; Insulin; Erythropoietin
Microscopic image analysis techniques for the morphological characterization of pharmaceutical particles: Influence of the software, and the factor algorithms used in the shape factor estimation
by Sergio Almeida-Prieto; José Blanco-Méndez; Francisco J. Otero-Espinar (pp. 766-776).
The present report highlights the difficulties of particle shape characterizations of multiparticulate systems obtained using different image analysis techniques. The report describes and discusses a number of shape factors that are widely used in pharmaceutical research. Using photographs of 16 pellets of different shapes, obtained by extrusion–spheronization, we investigated how shape factor estimates vary depending on method of calculation, and among different software packages. The results obtained indicate that the algorithms used (both for estimation of basic dimensions such as perimeter and maximum diameter, and for estimation of shape factors on the basis of these basic dimensions) have marked influences on the shape factor values obtained. These findings suggest that care is required when comparing results obtained using different image analysis programs.
Keywords: Image analysis; Granulation; Shape analysis; Extrusion; Spheronization; Morphology; Pellets
by Ingfried Zimmermann (pp. 777-778).