Physicochemical characterization and preliminary in vivo efficacy of bioadhesive, semisolid formulations containing flurbiprofen for the treatment of gingivitis

In this study, the physicochemical properties and preliminary in vivo clinical performance of formulations containing hydroxyethylcellulose (HEC; 3, 5, 10% w/w), poly(vinylpyrrolidone) (PVP; 3, 5% w/w), polycarbophil (PC; 1, 3, 5% w/w), and flurbiprofen (5% w/w) were examined. Flurbiprofen release into PBS pH 7.4 was performed at 37 degrees C. The mechanical properties (hardness, compressibility, adhesiveness, initial stress) and syringeability of formulations were determined using a texture analyzer in texture profile analysis (TPA) and compression modes, respectively. In general, the time required for release of 10 and 30% of the original mass of flurbiprofen (t10%, t30%) increased as the concentration of each polymeric component increased. However, in the presence of either 5 or 10% HEC and 5% PC, increased PVP concentration decreased both t10%, t30% due to excessive swelling (and disintegration) of these formulations. Increased concentrations of HEC, PVP, and PC significantly increased formulation hardness, compressibility, work of syringe expression, and initial stress due to the effects of these polymers on formulation viscoelasticity. Similarly, increased concentrations of PC (primarily), HEC, and PVP increased formulation adhesiveness due to the known bioadhesive properties of these polymers. Clinical efficacies of formulations containing 3% HEC, 3% PVP, 3% PC, and either 0% (control) or 5% (test) flurbiprofen, selected to offer optimal drug release and mechanical properties, were evaluated and clinically compared in an experimental gingivitis model. The test (flurbiprofen-containing) formulation significantly reduced gingival inflammation, as evaluated using the gingival index, and the gingival crevicular fluid volume, whereas, these clinical parameters were generally increased in volunteers who had received the control formulation. There were no observed differences in the plaque indices of the two subject groups, confirming that the observed differences in gingival inflammation could not be accredited to differences in plaque accumulation. This study has shown both the applicability of the in vitro methods used, particularly TPA, for the rational selection of formulations for clinical evaluation and, additionally, the clinical benefits of the topical application of a bioadhesive semisolid flurbiprofen-containing formulation for the treatment of experimental gingivitis.

Oleate salt formation and mesomorphic behavior in the propranolol/oleic acid binary system

Thermal analysis of propranolol/oleic acid mixtures prepared by solvent evaporation enabled construction of the binary system phase diagram. This allowed both physical and chemical interactions to be identified, including complex formation at the equimolar composition. An incongruent melting complex with a characteristic reaction point was identified in excess oleic acid compositions, a common property of fatty acid/fatty acid salt binary systems. The equimolar complex was confirmed to be propranolol oleate using infrared spectroscopy. Wide-angle X-ray powder diffractometry demonstrated that propranolol oleate possessed long-range positional order ( approximately 25 A d spacing) accompanied by a degree of disorder over shorter d spacings. Such a pattern suggested mesophase formation, explaining the unctuous nature of propranolol oleate at room temperature. Accurate measurement of the long-range d spacing was achieved using small-angle X-ray scattering, permitting differentiation of the three different phases identified (phase I: 25.4 A, phase II: 24.6 A, phase III: 25.4-25.5 A). The implications of drug fatty acid salt formation and also mesomorphism in pharmaceutical systems are discussed.

Water movement evaluation during extrusion of wet powder masses by collecting extrudate fractions

Water is normally the liquid of choice in extrusion/spheronisation systems. Its behaviour during the process is crucial to its success. In most extrusion formulations water moves under the pressures involved. It is important to understand how to control and limit water movement, and to understand its consequences. Five drug models were mixed with microcrystalline cellulose and with three different ratios of water and extruded at two different speeds using a ram extruder. Whilst extruding, the extrudates were collected to small fractions and dried to constant weight. Different parameters were calculated to quantify the extent of water movement that occurred. The same formulations were also extruded and than spheronised to pellets, for which size and shape factor were measured. The correlation between water level and extrusion force at the same given time was calculated. It was found that at the faster speed and in the wettest formulation there was less water movement. A significant correlation was found between extrusion force and water going through the die. The extrusion/spheronisation technique was found to be tolerant to some extent of water movement during the extrusion process. Nevertheless, excessive water movement is not appropriate.

Investigations into the structure and composition of beta-cyclodextrin/poly(acrylic acid) microspheres

Microspheres composed of the hydrophilic polymer poly(acrylic acid) (PAA), with and without beta-cyclodextrin (beta-CD), were prepared by a water-in-oil (w/o) solvent evaporation technique. Microspheres were characterised for particle size, beta-CD and residual oil content. The type of matrix formed during microsphere synthesis was investigated by solid state carbon 13C NMR, in vitro release of beta-CD and swelling measurements. A high encapsulation efficiency of the beta-CD was observed (?90%). The in vitro release of beta-CD in water over 24 h was initially rapid ( approximately 70% in 3 h) with no further loss thereafter, suggesting potential covalent binding of the residual beta-CD. NMR indicated that in the presence of beta-CD, two concomitant chemical processes occur during microsphere synthesis: (i) esterification of the hydroxyl group(s) of the beta-CD with the carboxylic acid groups of the PAA; and (ii) the formation of intra-/inter-polymer acid anhydrides.

Optimization of the mechanical properties and water-vapor transmission properties of free films of hydroxypropylmethylcellulose

Free films of hydroxypropylmethylcellulose were prepared by a spraying technique. Methocel E5 and Methocel E15 were used in varying proportions in the preparation of films. The free films were studied for their mechanical properties and moisture permeability characteristics. A 2(2) factorial design was used to quantitate the effect of each polymer on the tensile strength and permeability constant of the films.

In vitro release of cytarabine from swellable matrices of CnEmCn triblock copolymers

Matrices loaded with cytarabine were prepared by compression of the tailor made triblock copolymers C17E227C17 and C17E454C17 (where C=methylene and E=oxyethylene). Observations of the swelling characteristics of copolymer matrices on immersion in distilled water indicated an increase in the thickness of the gel layer around the matrices following ingress of water into the matrices. The in vitro release of cytarabine was characterised from matrices of different molar mass and with different known drug loadings. The release of cytarabine from the copolymer matrices was predominantly by a Fickian diffusion mechanism; the release rate was dependent on drug loading and independent of copolymer molar mass.

Erythropoietin loaded microspheres prepared from biodegradable LPLG-PEO-LPLG triblock copolymers: protein stabilization and in-vitro release properties

Biodegradable microspheres containing recombinant human Erythropoietin (EPO) were prepared from ABA triblock copolymers, consisting of hydrophobic poly(l-lactic-co-glycolic acid) A blocks and hydrophilic polyethylenoxide (PEO) B blocks. Different polymer compositions were studied for the microencapsulation of EPO using a modified double-emulsion process (W/O/W). The encapsulation efficiency for EPO, ranging from 72% to 99% was quite acceptable. The formation of high molecular weight EPO aggregates, however, was higher than in poly(d,l-lactide-co-glycolide) (PLG) microparticles. Using different excipients with known protein stabilizing properties, such as Bovine Serum Albumin (BSA), Poly-l-Histidine (PH), Poly-l-Arginine (PA) or a combination of PA with Dextran 40 (D40), the EPO aggregate content was significantly reduced to <5% of the encapsulated EPO. In contrast to PLG, ABA triblockcopolymers containing >7 mol % PEO, allowed a continuous release of EPO from microspheres for up to 2 weeks under in-vitro conditions. The release profile was comparable to FITC-Dextran 40 kDa (FD 40) loaded microspheres in the initial release phase, while EPO release was leveling off at later time points. BSA additionally prolonged the EPO release, while blends of PLG and PEO did not generate continuous EPO release profiles. LPLG-PEO-LPLG triblock-copolymers (35 mol % PEO; 30 kDa) in combination with 5% BSA yielded both an acceptable level of EPO aggregates and a continuous release profile under in-vitro conditions for up to 2 weeks. The formation of EPO aggregates at later time points is probably induced by acidic cleavage products of the biodegradable polymer and requires further optimization of the ABA polymer composition.

Polyethyleneglycol-stabilized manganese-substituted hydroxylapatite as a potential contrast agent for magnetic resonance imaging: particle stability in biologic fluids

RATIONALE AND OBJECTIVES

Polymer-stabilized manganese(II)-substituted hydroxylapatite (MnHA) has been investigated as a particulate contrast agent for magnetic resonance imaging. The MnHA core requires a polymer coating to retard opsonization, thereby prolonging its systemic persistence. Therefore, the aim of this study was to assess the stability of various formulations in biologic media in vitro.

METHODS

Polyethyleneglycol-coated manganese(II)-substituted hydroxylapatite particles were studied in bovine plasma as a function of the concentration of polymer in the formulation. Particle sizing techniques and nuclear magnetic resonance proton relaxometry were used to evaluate both in vitro and in vivo stability.

RESULTS

A small-sized particle (approximately 10 nm diameter) that is stable in bovine plasma and rabbit whole blood was formed in formulations with high amounts of polymer concentration. In formulations with low amounts of polymer concentration, larger-sized particles (approximately 100 nm diameter) were present along with the small-sized population. The larger particles de-aggregated into the small-size particle distribution on dispersion in bovine plasma and rabbit whole blood.

CONCLUSIONS

Ultrasmall particles with high surface coat were stable in plasma, whereas larger aggregates de-aggregated. Unlike Mn2+, the interaction of polyethyleneglycol-stabilized manganese(II)-substituted hydroxylapatite with plasma proteins was weak.

Enthalpy relaxation in binary amorphous mixtures containing sucrose

PURPOSE

To compare the enthalpy relaxation of amorphous sucrose and co-lyophilized sucrose-additive mixtures near the calorimetric glass transition temperature, so as to measure the effects of additives on the molecular mobility of sucrose.

METHODS

Amorphous sucrose and sucrose-additive mixtures, containing poly(vinylpyrrolidone) (PVP), poly(vinylpyrrolidone-co-vinyl-acetate) (PVPNA) dextran or trehalose, were prepared by lyophilization. Differential scanning calorimetry (DSC) was used to determine the area of the enthalpy recovery endotherm following aging times of up to 750 hours for the various systems. This technique was also used to compare the enthalpy relaxation of a physical mixture of amorphous sucrose and PVP.

RESULTS

Relative to sucrose alone, the enthalpy relaxation of co-lyophilized sucrose-additive mixtures was reduced when aged for the same length of time at a comparable degree of undercooling in the order: dextran approximately PVP > PVPNA > trehalose. Calculated estimates of the total enthalpy change required for sucrose and the mixtures to relax to an equilibrium supercooled liquid state (deltaHinfinity) were essentially the same and were in agreement with enthalpy changes measured at longer aging times (750 hours).

CONCLUSIONS

The observed decrease in the enthalpy relaxation of the mixtures relative to sucrose alone indicates that the mobility of sucrose is reduced by the presence of additives having a Tg that is greater than that of sucrose. Comparison with a physically mixed amorphous system revealed no such effects on sucrose. The formation of a molecular dispersion of sucrose with a second component, present at a level as low as 10%, thus reduces the mobility of sucrose below Tg, most likely due to the coupling of the molecular motions of sucrose to those of the additive through molecular interactions.

Effects of Tween 80 and sucrose on acute short-term stability and long-term storage at -20 degrees C of a recombinant hemoglobin

The addition of low levels of surfactant polyoxyethylene 20 sorbitan monooleate, Tween 80, to recombinant hemoglobin in phosphate-buffered saline minimized the level of protein aggregation during acute freeze-thaw studies. Addition of sucrose alone to the phosphate-buffered saline formulation, up to 0.5 M, provided minimal protection against freeze-thaw induced aggregation. In contrast to the acute stability studies, long-term storage at -20 degrees C induced aggregation and methemoglobin formation in those formulations containing only Tween 80 in phosphate-buffered saline. Addition of sucrose between 0.1 and 0.5 M to the formulation prevented formation of aggregates and severely arrested methemoglobin formation during the long-term -20 degrees C storage. Specific binding of Tween 80 to the hemoglobin was not observed using 16-doxyl stearic acid partitioning techniques with electron paramagnetic resonance. Minor structural changes to the protein secondary structure during freezing in the absence and presence of Tween 80 were observed with Fourier transform infrared spectroscopy. The alterations were partially prevented by addition of the sucrose. It is likely that the Tween 80 severely reduced protein aggregation during the acute stability studies by preventing the hemoglobin from reaching the air-liquid interface or the liquid-surface interfaces. The reduction in methemoglobin formation and aggregation observed during long-term storage can be accounted for on the premise that the sucrose reduced localized unfolding of the protein in a manner similar to the preferential exclusion theory (Arakawa, T.; and Timasheff, S. N. 1982, Biochemistry 1982, 21, 6536-6544). These studies demonstrate that acute formulation screening studies, albeit useful, may not necessarily predict protein stability during long-term storage.

Influence of dextran molecular weight on capture in and release from decylamine carboxymethylcellulose capsules

A series of dextran molecular weight markers were encapsulated in decylamine carboxymethylcellulose microcapsules to serve as probes of capsule retentivity. The capsules were prepared by allowing microdrops of aqueous sodium carboxymethylcellulose to fall into aqueous decylamine acetate solution. Salt exchange reaction at the droplet pseudointerface resulted in self-assembling films which essentially instantaneously enclosed the droplets. Concentrations of anionic polymer were varied in the range from 1-3%. Chromophore-bearing dextrans were incorporated into these capsules by blending the dextrans with the carboxymethylcellulose prior to the encapsulation step. Four dextrans of differing (light scattering) molecular weights were used: 2 x 10(6), 6 x 10(5), 7 x 10(4), and 1.9 x 10(4) amu. The mass balance of dextran retained in the capsules, released on washing the capsules or which escaped encapsulation was determined spectrophotometrically. To measure total dextran in a population of washed capsules, the capsules were lysed in a 0.3 M solution of sodium chloride. To monitor dextran release, washed capsules were suspended in water and dextran concentration in the supernatant was measured. Encapsulation efficiency exceeded 80% for high molecular weight dextran but was lower with the smaller dextrans.

Studies on immunodiagnosis of dracunculiasis. II. Search for circulating antigens

Sera from individuals living in a dracunculiasis endemic area of northern Ghana were examined for circulating Dracunculus medinensis antigens by applying protocols previously developed for detection of circulating antigens in other helminth infections. Antisera from rabbits immunised with homogenized first stage D. medinensis larvae were used for antigen capture and detection in three different forms, namely non-treated, biotinylated and horseradish peroxidase (HRP)-labelled. Three different preparations of human sera were examined, namely non-treated, pre-treated with polyethylene glycol/ethylenediaminetetra-acetic acid (PEG/EDTA) for analysis of precipitated immune complexes, and pre-treated with trichloroacetic acid (TCA) for analysis of isolated glycoproteins. In both SDS-PAGE/Western blotting and ELISA, significant reactivity was observed between non-treated and treated rabbit-antisera on the one hand and non-treated and treated human sera on the other. However, no significant response differences were observed between sera obtained from individuals with dracunculiasis and non-endemic controls. The reasons are analysed and possible explanations presented. The study provided no evidence that D. medinensis-specific circulating antigens, detectable by relatively simple means, occur in infected individuals.

Resistance to densification, tensile strength and capsule-filling performance of some pharmaceutical diluents

The purpose of this study was to compare some indicators of capsule-filling performance, as measured by tapped density under different conditions, and elucidate possible quantitative relationships between variation of capsule fill-weight (%CV) and gravitational and inter-particle forces (attractive or frictional) derived from measurements of particle size, true density, low compression and tensile strength. Five common pharmaceutical diluents (lactose, maize starch, talc, Emcocel and Avicel) were investigated and two capsule-filling methods (pouring powder and dosator nozzle) were employed. It was found that for the pouring-type method the appropriateness of Hausner's ratio (HR), Carr's compressibility index (CC%) and Kawakita's constant (alpha) as indicators of capsule fill-weight variation decreases in the order alpha > CC% > HR; the appropriateness of these indicators also decreases with increasing cylinder size and with impact velocity during tapping. For the dosator-type method the appropriateness of the indicators decreases in the order HR > CC% > alpha, the opposite of that for the pouring-type method; the appropriateness of the indicators increases with decreasing cylinder size and impact velocity. The relationship between %CV and the ratio of inter-particle attractive to gravitational forces calculated from measurements of particle size and true density (Fvdw/Wp) was more significant for the pouring-type capsule-filling method. For the dosator-type method a significant relationship (1% level) was found between %CV and the product of Fvdw/Wp and a function expressing the increase, with packing density (p(f)), in the ratio of frictional to attractive inter-particle forces derived from compression (P) and tensile-strength (T) testing, d(log(P/T))/d(p(f)). The value of tapped density in predictions of capsule-filling performance is affected by the testing conditions in a manner depending on the filling method applied. For the pouring-type method predictions can be based on the ratio of attractive (inter-particle) to gravitational forces, whereas for the dosator-type method the contribution of frictional and attractive forces should, because of packing density change, also be taken into account.

Optimization of an effervescent tablet formulation containing spray dried L-leucine and polyethylene glycol 6000 as lubricants using a central composite design

A rotatable central composite design is used to evaluate the effects of lubricants and compression force on the physical characteristics of effervescent tablets. Effervescent tablets lubricated with a combination of spray dried L-leucine and polyethylene glycol 6000 are prepared by direct compression and examined. Residual force, crushing strength and disintegration time are considered as response variables and related to the L-leucine and polyethylene glycol concentrations and to the compression force. The calculated models are used to assess the influence of the production factors on tablet properties. As increasing amounts of L-leucine, showing good lubricating properties, reduce the crushing strength and prolong tablet disintegration, the L-leucine concentration is kept at a low level. An optimum tablet formulation contains 2% L-leucine and 3% polyethylene glycol 6000. The tablets have a tensile strength of 0.47 MPa and disintegrate in less than 2 min. Predicted and experimental results are in agreement within a 95% CI.

The pH-independent release of fenoldopam from pellets with insoluble film coats

Various ratios of succinic acid to fenoldopam mesylate, ranging from 0:1 to 18:1 were incorporated in pellets and coated with 1.5-12% w/w Surelease. Even though the coating level did influence the rate and amount of fenoldopam release, the influence of the succinic acid to drug ratio was much more important and evident at all coating levels. Being a weakly basic drug, fenoldopam release ceased when testing in SIF for succinic acid to drug ratios of 0:1-4:1, with the end of release being more abrupt for the 0:1 than for the 4:1 ratio. Only for a succinic acid to drug ratio of > or =5 was fenoldopam release constant for 6-8 h and independent of the pH-value of dissolution media. For a thin coat of about 2.5% w/w Surelease, those pellets showed an ideal controlled release behaviour with release rates of about 5-10%/h and a total release of almost 80% in 8 h. The dissolution profiles of Surelease coated pellets with high succinic acid to drug ratios (> or =5) and different coating levels, were evaluated for best fits to commonly used kinetic models. Sustained release mechanisms are discussed according to best fit models. The quantification of the pH-adjuster succinic acid, released from pellets with an acid to drug ratio of < or =1 showed, that despite their failure as a controlled release system for fenoldopam, the investigated coats could control the release of succinic acid effectively at optimized coating levels. For increasing succinic acid to drug ratios (< or =4) succinic acid was released at an ever more constant rate and release rates, though still faster than the release rates of fenoldopam, decreased steadily for increasing ratios. At a 5:1 ratio finally release rates of succinic acid and fenoldopam were almost identical. Therefore those pellet cores were almost completely emptied during dissolution testing, with both fenoldopam and succinic acid leaving at a constant rate and a total release of about 80% each for a 2.5% Surelease coat, while lower succinic acid to drug ratios had failed to show any sustained release for such thin Surelease coats. A similar formulation with fumaric acid instead of succinic acid failed to show the desired release pattern, indicating that it is the presence of a sufficiently high amount of succinic acid rather than the presence of an acidic compound in general, that ensures fenoldopam solubility at higher pH-values.

Improving stability and release kinetics of microencapsulated tetanus toxoid by co-encapsulation of additives

PURPOSE

Tetanus toxoid (Ttxd) encapsulated in polyester microspheres (MS) for single injection immunization have so far given pulsatile in vitro release and strong immune response in animals, but no boosting effect. This has been ascribed to insufficient toxoid stability within the MS exposed to in vivo conditions over a prolonged time period. This study examined the effect of co-encapsulated putative stabilizing additives.

METHODS

Two different Ttxd were encapsulated in poly(D,L-lactic-co-glycolic acid) (PLGA 50:50) and poly(D,L-lactic acid) (PLA) MS by spray-drying. The influence of co-encapsulated additives on toxoid stability, loading in and release from the MS, was studied by fluorimetry and ELISA.

RESULTS

Co-encapsulated albumin, trehalose and gamma-hydroxypropyl cyclodextrin all improved the toxoid encapsulation efficiency in PLGA 50:50 MS. Albumin increased the encapsulation efficiency of antigenic Ttxd by one to two orders of magnitude. Further, with albumin or a mixture of albumin and trehalose ELISA responsive Ttxd was released over 1-2 months following a pulsatile pattern.

CONCLUSIONS

Optimized Ttxd containing MS may be valuable for a single-dose vaccine delivery system.

Influence and optimisation of operating parameters with a new binder in wet granulation. I: use in powder form

It is very important to know the properties of a new binder in wet granulation because it involves the good or poor quality of the grain and the tablets. To estimate the effects of various procedural parameters on the tablet properties, to evaluate the optimal quantity of binder and solvent, the consequences of excess solvent or time mixing and to limit the number of experiments, the authors use the method of design of experiments. The experiments were carried out on a classical blend of lactose and maize starch and the binder was LYCATAB DSH, a maltodextrin. In this first part the binder was used in powder form and three process factors were retained and controlled, the binder quantity, the quantity of wetting liquid and the mixing time after granulation. Different outcomes were measured and mathematical relationships between responses and operating factors were performed and discussed. A 4% binder concentration with 14-16% of solvent gives good results and an increase in mixing time improves the tablet hardness without increasing the disintegration time (the wetting liquid was water and the blender a LOEDIGE).

The effect of an increase in chain length on the mechanical properties of polyethylene glycols

The mechanical properties of different molecular weights of polyethylene glycol (PEG) have been determined by formation of compacted tablets and beams, which were subjected to diametral compression and 3-point bending, respectively. From diametral compression, the tensile strength for the different grades of PEG was determined. Flat beams made from powder by compaction were used to determine Young's modulus of elasticity. Beams into which a notch had been introduced after formation allowed the fracture mechanical parameters of critical stress intensity factor, K(IC), and fracture toughness, R, to be determined. Evaluation of these parameters as a function of compact porosity allowed extrapolation to values at zero porosity, providing an estimate of the material properties. The increase in chain length of the PEG was found to have a non-linear effect on tensile strength and Young's modulus. The ductility of the polymer increased proportionally to the increase in chain length, reflected by the linear relationship between K(IC) and the molecular weight. Young's modulus and critical stress intensity factor allowed the estimation of the strain energy release rate, G(IC), which is the driving force in crack propagation. Consequently, the tensile strength at zero porosity was found to be predictable from the values of G(IC) and the molecular weight of the different grades of PEG.

Effect of sodium metabisulfite on hydrogen peroxide production in light-exposed pediatric parenteral amino acid solutions

The effect of sodium metabisulfite (MBS) on hydrogen peroxide (HP) production in model and commercial amino acid solutions exposed to phototherapy light was studied. Model and commercial pediatric amino acid solutions were prepared such that the amino acid concentration was 1%. MBS concentration, riboflavin concentration, and duration of exposure to phototherapy light were varied to determine the effect on HP production. Control solutions were kept in the dark. HP production was assayed in the model amino acid solutions by using potassium iodide in the presence of ammonium molybdate. In all experiments, HP production was measured at 360 nm in the presence and absence of catalase. In light-exposed solutions, HP production increased linearly for several hours and reached a plateau by eight hours. A mean maximum of 940 microM was produced (data pooled for all solutions). No detectable HP was generated in the solutions kept in the dark. After two hours of light exposure, it was necessary to add at least 10 times more MBS than is typically found in commercial total parenteral nutrient solutions to scavenge all the HP produced. An average of up to 940 microM of HP was produced in model and commercial pediatric parenteral 1% amino acid solutions in the presence of phototherapy light and clinically relevant concentrations of riboflavin and MBS. Light exposure decreased the antioxidant effect of MBS.

Stability of enalapril maleate in three extemporaneously prepared oral liquids

The stability of enalapril 1 mg/mL (as the maleate) in deionized water, citrate buffer solution, and a sweetened suspending agent at two temperatures was studied. Twenty enalapril 10-mg tablets were crushed to a powder. Deionized water, citrate buffer solution, or sweetened vehicle was added to produce three 200-mL batches of each liquid; the expected final concentration of enalapril in each was 1 mg/mL. Each formulation was stored in 10 60-mL bottles, 5 of which were stored at 4 degrees C and 5 at 25 degrees C. Samples were collected on days 0, 7, 14, 28, 42, 56, 70, and 91 for visual inspection and analysis by high-performance liquid chromatography; pH was measured at each sampling time as well. The mean concentration of enalapril in the three liquids at 4 degrees C was > 94% of the initial concentration throughout the 91-day study period. At 25 degrees C, the mean concentration of enalapril was > 90% for 56 days and > 92% for 91 days in both citrate buffer solution and sweetened vehicle. The pH of the liquid prepared with deionized water and stored at 25 degrees C decreased by 2.0 pH units. Enalapril 1 mg/mL (as the maleate) in three extemporaneously compounded oral liquids was stable for 91 days at 4 and 25 degrees C with the exception of enalapril in deionized water, which was stable for only 56 days at 25 degrees C.

Coumarin-based prodrugs. Part 3: Structural effects on the release kinetics of esterase-sensitive prodrugs of amines

To study the structural effects on the release kinetics of a coumarin-based esterase-sensitive prodrug system, two series of compounds with varying structural features of the ester 'trigger' part and the amine 'drug' part were synthesized. The half-lives of the nine model prodrugs in the presence of porcine liver esterase ranged from about 2 min to 190 min. The steric bulkiness of the acyl group seems to have only a very minor effect on the half-lives of the esterase-triggered release of amines from the model prodrugs. The rate of the lactonization depends on the steric and electronic properties of the amine moiety.

Mechanochemical solid-state polymerization. VIII. Novel composite polymeric prodrugs prepared by mechanochemical polymerization in the presence of pharmaceutical aids

We carried out the mechanochemical polymerization of methacryloyl derivatives of acetoaminophen and 5-fluorouracil in the presence of lactose. The reaction proceeded readily and the polymeric prodrugs were quantitatively produced. This method produces powdered polymeric prodrugs in which fine particles of lactose are homogeneously dispersed, since the reaction proceeds quantitatively through a totally dry process. It is difficult to prepare such a powdered polymeric prodrug by conventional solution polymerization. The rate of drug release of polymeric prodrugs increases with increasing content of lactose, as is shown to be true of the specific surface of polymeric prodrugs. These results suggest that lactose is homogeneously dispersed in powdered polymeric prodrugs. The present method seems applicable to a wide variety of pharmaceutical aids. If one takes the physiochemical property of pharmaceutical aids into consideration, novel polymeric prodrugs with a variety of drug release rates can be synthesized simultaneously with mixing.

Non-antigenic and low allergic gelatin produced by specific digestion with an enzyme-coupled matrix

Porcine gelatin (heat-denatured collagen) was digested with a bioreactor using an enzyme-coupled matrix (ECM) with purified collagenase. The digested gelatin, FreAlagin type R (M.W. range 200-10000 Da), was further purified by an HPLC system depending upon molecular size. The molecular weight range of the purified fractions, FreAlagin type P and type AD, were 200-500 and 2000-10000 Da, respectively, and glycine was the N-terminal amino acid of both types (> or =93%). ECM has the capability of digesting gelatin at a specific point in the sequence before glycine, and it was determined that FreAlagin type P consists of a tri-peptide fraction with the amino acid sequence Gly-X-Y. No types of FreAlagin exhibited any reactivity with gelatin-specific IgG antibody raised in guinea pigs, and they also possessed an extremely low reactivity with gelatin-specific IgE antibody from the sera of patients who had experienced an anaphylactic reaction against gelatin after vaccination or after eating gelatin-containing foods. From these results, it was determined that FreAlagin types R and AD were non-antigenic, low-allergic gelatins. FreAlagin type R, and especially type AD, had strong adsorption-blocking activity comparable to the level of bovine serum albumin, whereas type P and glycine had virtually no adsorption-blocking activity. Therefore, the new types of gelatin, FreAlagin types R and AD, are suitable for pharmaceutical use to avoid gelatin allergy.

The adsorption of cellulose ethers in aqueous suspensions of pyrantel pamoate: effects on zeta potential and stability

This work examined the physico-chemical phenomena induced in aqueous suspensions of pyrantel pamoate by two varieties of hydroxypropylmethylcellulose (HPMC) and sodium carboxymethylcellulose (NaCMC) of different molecular weights, and the effects of these phenomena on the physical stability of the suspension. The mechanism of the interfacial adsorption of the polymer was investigated by constructing adsorption isotherms: for the two HPMC varieties, the isotherms were of type L and were fitted with the Langmuir model; of the NaCMCs, only the variety with higher molecular weight was adsorbed, its adsorption isotherm being of type S (sigmoidal). The resulting monolayer films were characterized viscosimetrically, determining their thickness and the number of polymer molecules adsorbed per unit area. The nonionic polymers formed thinner, more continuous monolayers than the NaCMC. Only the nonionic polymers significantly altered the zeta potential of the systems. In the range of conditions studied, all the polymers stabilized the initially flocculated systems, decreasing sedimentation volume and increasing the time necessary to redisperse them (the redispersability value). This stabilization occurred either by the steric mechanism (HPMCs and the high-molecular-weight NaCMC) or by depletion mechanisms (low-molecular-weight NaCMC). Owing to the complexity of these mechanisms, sedimentation volume was not found to be a useful index of the consistency of the sediments obtained from the suspensions.

Collagen--biomaterial for drug delivery

The use of collagen as a biomaterial is currently undergoing a renaissance in the tissue engineering field. The biotechnological applications focus on the aspects of cellular growth or delivery of proteins capable of stimulating cellular response. However, basic knowledge about collagen biochemistry and the processing technology in combination with understanding of the physico-chemical properties is necessary for an adequate application of collagen for carrier systems. The purpose of this review article is to summarize information available on collagen dosage forms for drug delivery as well as to impart an overview of the chemical structures and the galenical properties including detailed description of the processing steps - extraction, purification, chemical crosslinking and sterilization. The most successful and stimulating applications are shields in ophthalmology, injectable dispersions for local tumor treatment, sponges carrying antibiotics and minipellets loaded with protein drugs. However, the scientific information about manipulating release properties or mechanistic studies is not as abundant as for some synthetic polymers.