International Journal of Pharmaceutics (v.198, #1)
Stability assessment of ketoconazole in aqueous formulations by M. Skiba; M. Skiba-Lahiani; H. Marchais; R. Duclos; P. Arnaud (1-6).
Ketoconazole is an imidazole antifungal agent. It has a wide antifungal spectrum and possesses some antibacterial activity. In inappropriate formulations, especially in aqueous media, ketoconazole molecules may be unsteady. The stability of ketoconazole in aqueous media was assessed as a function of pH, antioxidant and ketoconazole concentrations. It was found that ketoconazole was least stable at pH 1 among the pH values studied (pH 1–9). Since the major degradation pathway was specific acid catalysis, based upon the transition-state theory, the entropy (ΔS) of the activation was calculated and found to be negative indicating that the activated complex was more constrained than the individual species. The free energy of activation (ΔG) was estimated to be 30 kcal mol−1. The viscosity of the formulation was found to be more stable at high pH because carbopol is stable at basic pH and protected ketoconazole. It appears that the amount of ketoconazole in the formulation has a low influence on the degradation mechanisms. The increase of the butylated hydroxytoluene antioxidant levels from 0.05 to 0.4%, adversely affected the stability of ketoconazole. In conclusion, the expected shelf life of the final ketoconazole formulation (pH 7, 0.1% butylated hydroxytoluene) was 15 months.
Keywords: Ketoconazole; Stability; Antioxidant; Entropy; Free energy;
Nonionic oil-in-water microemulsions: the effect of oil type on phase behaviour by W. Warisnoicharoen; A.B. Lansley; M.J. Lawrence (7-27).
The formation of oil-in-water (o/w) microemulsions stabilized by the nonionic surfactants, polyoxyethylene-10-dodecyl ether, polyoxyethylene-10-oleyl ether, N,N-dimethyldodecylamine-N-oxide and N,N-dimethyloleylamine-N-oxide and containing a variety of pharmaceutically acceptable oils, namely ethyl butyrate, ethyl caprylate, ethyl oleate and the triglycerides, soybean oil, Miglyol 812 and tributyrin, has been examined at 298 K. The effect on microemulsion formation of replacing water with phosphate buffered saline (PBS) and complete PBS has been established. In addition, the effect of changing temperature (from 298 to 310 K) on the phase behaviour of microemulsions formulated using PBS as continuous phase has been determined. Although some small differences in phase behaviour were noted when altering the continuous phase, the greatest difference in phase behaviour was observed when changing the experimental temperature, particularly for microemulsions stabilized by polyoxyethylene-10-oleyl ether. Regardless of the temperature and aqueous phase used, however the larger molecular volume oils (soybean oil, Miglyol 812 and ethyl oleate) were solubilized to a lower extent than the smaller molecular volume oils (namely, ethyl butyrate and ethyl caprylate). The only exception to this rule was when polyoxyethylene-10-oleyl ether was used as surfactant, particularly at 298 K, where it was the larger molecular volume oils that were solubilized to the greatest extent. Cloud point/phase inversion temperature experiments suggested that the higher molecular volume oils were incorporated into the microemulsions prepared using the polyoxyethylene-based surfactants in a different way than the smaller molecular volume oils and suggest that the smaller molecular volume oils are acting in much the same way as a cosurfactant in that they interchelate with their hydrophilic group interspersed in the surfactant head group region. As N,N-dimethyldodecylamine-N-oxide does not exhibit a cloud point it was not possible to determine the mode of oil incorporation in microemulsions prepared with this surfactant.
Keywords: Nonionic oil-in-water microemulsions; Polyoxyethylene ether surfactants; N,N-Dimethyl-alkylamine-N-oxide surfactants;
Prolonged effect of liposomes encapsulating pilocarpine HCl in normal and glaucomatous rabbits by A.Soltan Monem; Fadel M Ali; Medhat W Ismail (29-38).
The possibility of using liposomes as an ophthalmic drug delivery carrier for the lipophilic drug, pilocarpine HCl, was investigated on the eyes of normal and glaucomatous pigmented rabbits. The intraocular pressure (IOP) of rabbits was measured, using a Shi∅tz tonometer, as a function of time after topical administration with free drug, neutral and negatively charged multilamellar vesicles (MLVs) encapsulating pilocarpine HCl. The results showed that administration with neutral MLVs displayed the most prolonged effect with respect to negatively charged MLVs and free drug. The efficiency of MLVs encapsulating pilocarpine HCl, measured using spectrophotometric technique, was found to be 96% in our modified preparations. The storage stability of MLVs encapsulating pilocarpine HCl was investigated by measuring phase transition and size distribution using light scattering technique. The results show that liposomes encapsulating pilocarpine HCl have kept their integrity and physicochemical properties for at least 15 months, which makes them suitable for commercial use.
Keywords: Liposome characterization; Pilocarpine hydrochloride; Glaucomatous pigmented rabbits; Intraocular pressure (IOP); Light scattering;
Improved kinetic parameter estimation in pH-profile data treatment by Issa T Some; Philippe Bogaerts; Raymond Hanus; Michel Hanocq; Jacques Dubois (39-49).
Statistical problems in temperature stability parameter estimation have been the subject of many papers whereas statistics in, pH-profile parameter estimation have focused little attention. However, the conventional two step method used in data treatment in both cases leads to identical statistical problems. The aim of this study is then to introduce a method that improves statistics in pH-profile parameter estimation. A one step non-linear method that takes into account the errors in drug content determination is proposed. A mathematical relationship between drug content C, pH and time t is tested. The proposed method allows the estimation of the specific kinetic constants and the dissociation constant (pK a) in a single run. The most likely experimental initial drug contents C 0j ,. where j is the index of a given experiment, are also determined. This approach that takes into account all relevant experimental information for the estimation of kinetic parameters is more rigorous from a statistical viewpoint than the classical two step methods. Kinetic data from acetylsalicylic acid (ASA) hydrolysis was used for the tests.
Keywords: Acetylsalicylic acid; Stability; pH-profile; Non-linear fitting; Simplex algorithm;
Effect of process parameters on compressibility of granulation manufactured in a high-shear mixer by Sherif I.Farag Badawy; Mark M. Menning; Mary Ann Gorko; Donna L. Gilbert (51-61).
Various processing variables that can influence granulation characteristics of a lactose-based formulation were evaluated using a Plackett–Burman experimental design. These parameters were impeller speed, granulating solution addition rate, total amount of water added in the granulation step, wet massing time, moisture content of the granulation after drying, and screen size used for the dry milling. Results showed that granulation growth was enhanced by the increase in the amount of added water, high impeller speed, and short wet massing time. On the other hand, moisture content had the largest impact on granulation compressibility, followed by the wet massing time and impeller speed. Increasing moisture content of the granulation and decreasing wet massing time or impeller speed increased granulation compressibility. Increasing impeller speed and/or wet massing time decreased granule porosity and fragmentation propensity, which led to decreased granulation compressibility. Granulation compressibility was extremely sensitive to processing conditions. Tablets from all runs showed acceptable weight variation and friability, suggesting that the parameters evaluated had little effect on these responses in the ranges tested.
Keywords: Granulation; High shear; Lactose; Compressibility; Porosity;
Comparison of in vitro and in vivo efficiencies of a novel unit-dose liquid aerosol generator and a pressurized metered dose inhaler by Stephen J. Farr; Simon J. Warren; Peter Lloyd; Jerry K. Okikawa; Jeffrey A. Schuster; Antony M. Rowe; Reid M. Rubsamen; Glyn Taylor (63-70).
Gamma scintigraphic imaging was employed in 10 healthy volunteers to compare the total and regional lung deposition of aerosols generated by two delivery platforms that permitted microprocessor-controlled actuation at an optimal point during inhalation. An aqueous solution containing 99mTc-DTPA was used to assess the deposition of aerosols delivered by inhalation from two successive unit-dosage forms (44 μl volume) using a prototype of a novel liquid aerosol system (AERx™ Pulmonary Delivery System). This was compared with aerosol deposition after inhalation of two 50 μl puffs of a 99mTc-HMPAO-labeled solution formulation from a pressurized metered dose inhaler (MDI). The in vitro size characteristics of the radiolabeled aerosols were determined by cascade impaction. For the AERx system, the predicted lung delivery efficiency based on the product of emitted dose (60.8%, coefficient of variation (CV)=12%) and fine particle fraction (% by mass of aerosol particles <5.7 μm in diameter) was 53.3% (CV=13%). For the solution MDI, the emitted dose was 62.9% (CV=13%) and the predicted lung dose was 44.9% (CV=15%). The AERx system demonstrated efficient and reproducible dosing characteristics in vivo. Of the dose loaded into the device, the mean percent reaching the lungs was 53.3% (CV=10%), with only 6.9% located in the oropharynx/stomach. In contrast, the lung deposition from the solution MDI was significantly less (21.7%) and more variable (CV=31%), with 42.0% of the radiolabel detected in the oropharynx/stomach. Analysis of the regional deposition of the radioaerosol indicated a homogeneous pattern of deposition after delivery from the AERx system. A predominantly central pattern of distribution occurred after MDI delivery, where the pattern of deposition was biased towards a central zone depicting the conducting airways. The AERx system, in contrast to MDIs, seems highly suited to the delivery of systemically active agents via pulmonary administration.
Keywords: Aerosol deposition; Metered dose inhaler; Liquid aerosol generator; Microprocessor-controlled device; Gamma scintigraphy;
Synthesis and bacterial degradation of an azopolymer by S.Hashem Soozandehfar; Janine L Bragger; Gary P Martin; Andrew W Lloyd (71-82).
Azopolymers were synthesised with differing degrees of hydrophobicity, from 2-hydroxyethylmethacrylate (HEMA), styrene and 2,2′-dimethylacryloyloxyazobenzene as azo crosslinker. Bacterial degradation of the series of polymers was assessed using a pure culture of the colonic organism Enterococcus faecalis and rat caecal contents. Polymer degradation was determined in terms of weight loss on polymer coated glass beads and using scanning electron microscopy after incubation. Similar weight loss occurred on incubation of polymers in both bacterial cultures and non-bacterial control. The presence of styrene was found to decrease the amount of weight loss. The polymer surfaces showed microscopic cracks and holes after incubation, again, this phenomenon was less pronounced with increasing styrene content. As there was no increase in polymer degradation in the presence of azo reducing microorganisms, the results of this study suggest that these polymers are degraded by mechanisms other than azo reduction.
Keywords: Azopolymers; HEMA; Styrene; 2,2′-Dimethylacryloyloxyazobenzene; Bacterial degradation;
Modulating pharmacokinetics of an anti-interleukin-8 F(ab′)2 by amine-specific PEGylation with preserved bioactivity by Iphigenia Leonidou Koumenis; Zahra Shahrokh; Steven Leong; Vanessa Hsei; Laura Deforge; Gerardo Zapata (83-95).
By covalently attaching biocompatible polyethylene-glycol (PEG) groups to ε-amino groups of the F(ab′)2 form of a humanized anti-interleukin-8 (anti-IL-8) antibody, we sought to decrease the in vivo clearance rate to give a potentially more clinically acceptable therapeutic. The in vivo clearance was modulated by changing the hydrodynamic size of the PEGylated antibody fragments. To achieve significant increases in the hydrodynamic size with minimal loss in bioactivity, high molecular weight linear or branched PEG molecules were used. Modification involved N-hydroxy-succinamide reaction of the PEGs with primary amines (lysines and/or the N-terminus) of the anti-IL-8 F(ab′)2. The process of adding up to four linear 20 kDa PEG, or up to two branched 40kDa PEG, gave reproducible distribution of products. The components with uniform size (as assessed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis) were purified by a single-step ion-exchange high-performance liquid chromatography and showed no significant loss of biological activity in ligand binding and cell-based assays. Addition of a single branched 40 kDa PEG to a F(ab′)2 (molecular weight (MW)=1.6 million Da) or up to two 40 kDa branched PEG (MW=1.9 million Da) increased the serum half-life to 48 h as compared with the unPEGylated F(ab′)2 with a half-life of 8.5 h. This study shows that by attaching high molecular weight PEGs at a one or two sites, bioactive antibody fragments can be made reproducibly with sizes tailored to achieve the desired pharmacokinetics.
Keywords: Pharmacokinetics; Polyethylene-glycolylation; Bioactivity; Anti-interleukin-8 antibody;
Chitosan citrate as film former: compatibility with water-soluble anionic dyes and drug dissolution from coated tablet by Thawatchai Phaechamud; Tamotsu Koizumi; Garnpimol C. Ritthidej (97-111).
Chitosan citrate solution containing 25% w/w propylene glycol was prepared and tested for its compatibility with some water soluble anionic dyes. The immiscibility between erythrosine, ponceau 4R, sunset yellow or tartrazine solutions and chitosan citrate solution was evident. The Fourier transform-infrared spectra revealed charged interaction between anionic dye and chitosan. Brilliant blue and green FS at concentration of 0.02–1.00% w/w polymer could be miscible with chitosan citrate solution due to the decrease in charge interaction by the positive charge on molecule of brilliant blue, which was also the composition in green FS. Propranolol HCl tablets coated with these colored film-coating solutions exhibited good appearance and no color migration. Drug dissolution from coated tablets was pH dependent, corresponding to the ability of chitosan to protonate in the medium. Color incorporation slightly retarded drug dissolution in acidic medium. Drug dissolved from coated tablet colored with brilliant blue was faster than from that colored with green FS. This was because brilliant blue had positive charge and more SO3H groups on its molecular structure, and exhibited higher water solubility. Accelerated condition could alter dissolution characteristics, and the Td+t 0 value from curve fitting between the dissolution profiles and Weibull equation was increased. However, drug dissolution from freshly prepared coated tablets, coated tablets after exposure to accelerated condition and after storage at room temperature for 12 months conformed to the monograph in USP XXIII.
Keywords: Chitosan citrate; Film former; Coated tablet; Water-soluble anionic dye; Compatibility;
Thermodynamic analysis of compact formation; compaction, unloading, and ejection by Mark T. DeCrosta; Joseph B. Schwartz; Rodney J. Wigent; Keith Marshall (113-134).
The aim of this investigation was to determine and evaluate the thermodynamic properties, i.e. heat, work, and internal energy change, of the compaction process by developing a ‘Compaction Calorimeter’. Compaction of common excipients and acetaminophen was performed by a double-ended, constant-strain tableting waveform utilizing an instrumented ‘Compaction Simulator.’ A constant-strain waveform provides a specific quantity of applied compaction work. A calorimeter, built around the dies, used a metal oxide thermistor to measure the temperature of the system. A resolution of 0.0001°C with a sampling time of 5 s was used to monitor the temperature. An aluminum die within a plastic insulating die, in conjunction with fiberglass punches, comprised the calorimeter. Mechanical (work) and thermal (heat) calibrations of the elastic punch deformation were performed. An energy correction method was outlined to account for system heat effects and mechanical work of the punches. Compaction simulator transducers measured upper and lower punch forces and displacements. Measurements of the effective heat capacity of the samples were performed utilizing an electrical resistance heater. Specific heat capacities of the samples were determined by differential scanning calorimetry. The calibration techniques were utilized to determine heat, work, and the change in internal energies of powder compaction. Future publications will address the thermodynamic evaluation of the tablet sub-processes of unloading and ejection.
Keywords: Compaction; Unloading; Ejection; Decompression; Calorimetry; Compaction calorimeter; Compaction work; Compaction heat; Internal energy change; Punch deformation;