Development of a Novel Controlled-Release System for Gastric Retention

Purpose. We report on the development of a novel controlled-release gastric retention system, which consists of a matrix tablet, coated with a permeable membrane. When immersed in simulated gastric fluid, the tablet expands. The tablet remains expanded for eighteen to twenty hours, during which time the drug is released. The tablet then either disintegrates into fragments or loses its integrity. Methods. Tablets containing a soluble drug (chlorpheniramine maleate, i.e., CPM) and a poorly soluble drug (riboflavin 5 phosphate, i.e., R5P) were compressed. They were coated with a permeable and elastic polymer (Eudragit^®). Dissolution profiles of these tablets were studied. The changes in the pH, viscosity, and deformation characteristics as a function of time were measured. Results. Carbopol^® provided a firm structure to the swollen tablet. Polyvinyl pyrrolidone XL (PVP XL) contributed to the swelling of the tablet. Carbonates provided the initial alkaline micro-environment for Carbopol^® to gel and conferred buoyancy to the tablet. Coating provided the support needed for the core to remain intact during drug release and, at the same time, it allowed drug release due to its permeable nature. During release, the gelling properties of Carbopol^® lessened, resulting in a decrease in the firmness of the core. This was evident from the decrease in the viscosity of the core. The energy required at 50% strain also decreased as the drug release progressed. Conclusions. When this tablet is ingested, the chances of its elimination through the pylorus should be greatly reduced due to tablet's expansion, and due to its disintegration or loss in integrity it should then be expelled out of the stomach at the end of the drug release.     

Improved inhalation behavior of steroid KSR-592 in vitro with Jethaler by polymorphic transformation to needle-like crystals (beta-form)

Purpose. The aim of the present study was to improve the dry powder inhalation behavior of steroid KSR-592 with lactose by altering the crystal shape and the particle size of the drug for use in a newly designed inhalation device, Jethaler®. Method. The shape of the crystals was changed by polymorphic transformation of original crystal (-form) to -form by agitating -form crystals in hexane containing 5% ethanol. The inhalation properties of the resultant crystals in vitro were evaluated with a twin impinger and cascade impactor. Results. Needle-like crystals (-form) with dimensions of 1.8 m in width × 41m in length were obtained by the polymorphic transformation, the kinetics of which was described by the Avrami equation. The -form crystals loaded on lactose particles were easily separated and crushed into fine particles in the airstream produced in the Jethaler®, which increased dramatically the respirable fraction (RF) deposited in the twin impinger (43.8%) and the fine particle fraction (FPF) of the cascade impactor (FPF = 39.3%) compared with their values for the original crystals (RF = 5.8%, FPF = 4.7%). Conclusion. The dry powder inhalation properties of steroid KSR-592 (platelike crystal, -form) were improved dramatically by changing the crystal shape to a needle-like shape by the polymorphic transformation to the -form.     

Macroflux® Microprojection Array Patch Technology: A New and Efficient Approach for Intracutaneous Immunization

Purpose. We evaluated the Macroflux® microprojection array patch technology as a novel system for intracutaneous delivery of protein antigens. Methods. Macroflux® microprojection array systems (330-m microprojection length, 190 microprojections/cm², 1- and 2-cm² area) were coated with a model protein antigen, ovalbumin (OVA), to produce a dry-film coating. After system application, microprojection penetration depth, OVA delivery, and comparative immune responses were evaluated in a hairless guinea pig model. Results. Macroflux® microprojections penetrated into hairless guinea pig skin at an average depth of 100 m with no projections deeper than 300 m. Doses of 1 to 80 g of OVA were delivered via 1- or 2-cm² systems by varying the coating solution concentration and wearing time. Delivery rates were as high as 20 g in 5 s. In a prime and boost dose immune response study, OVA-coated Macroflux® was most comparable to equivalent doses injected intradermally. Higher antibody titers were observed when OVA was administered with the microprojection array or intradermally at low doses (1 and 5 g). Macroflux® administration at 1- and 5-g doses gave immune responses up to 50-fold greater than that observed after the same subcutaneous or intramuscular dose. Dry coating an adjuvant, glucosaminyl muramyl dipeptide, with OVA on the Macroflux® resulted in augmented antibody responses. Conclusions. Macroflux® skin patch technology provides rapid and reproducible intracutaneous administration of dry-coated antigen. The depth of skin penetration targets skin immune cells; the quantity of antigen delivered can be controlled by formulation, patch wearing time, and system size. This novel needle-free patch technology may ultimately have broad applications for a wide variety of therapeutic vaccines to improve efficacy and convenience of use.     

Comparison of the Hanson Microette® and the Van Kel Apparatus for In Vitro Release Testing of Topical Semisolid Formulations

Purpose. The major goal of this study was to compare the relative utility of the Hanson Microette® and the Van Kel apparatus, two fully automated devices, as in vitro release tests (IVRT) for semisolids. We attempted to develop methodology that can be used to discriminate formulation changes, and to evaluate the precision, reproducibility and technical complexity of each test apparatus. Methods. We chose the sunscreen Eusolex®232 (2-Phenylben- zimidazole-5-sulfonic acid) as a model compound, which was incorporated into an emulsion formulation prepared in our laboratory. Test conditions for the two IVRT were made as nearly identical as possible, in order to obtain an accurate comparison. Results. The formulations were tested and found to be physically stable throughout the entire study. Diffusion coefficients were apparatus-dependent but were independent of the drug concentration in the formulations. The IVRT data were plotted as amount released (g/cm²) vs. square root of time (s^0.5) and a linear relationship was obtained in each case. Both methods produced similar results and were able to detect changes in drug loading in the formulations. Conclusions. The linear relationship between the amount released and the square root of time indicates a diffusion-controlled release of drug. Both apparatuses proved to be suitable as tests for formulation sameness according to the FDA's SUPAC-SS guidelines, during level 3 changes. However, each apparatus produced a different release profile for the drug. The choice of apparatus will depend upon a number of considerations.     

The Mechanism of Uptake of Biodegradable Microparticles in Caco-2 Cells Is Size Dependent

Purpose. To study the uptake of biodegradable microparticles in Caco-2 cells. Methods. Biodegradable microparticles of polylactic polyglycolic acid co-polymer (PLGA 50:50) of mean diameters 0.1 m, 1 m, and 10 m containing bovine serum albumin as a model protein and 6-coumarin as a fluorescent marker were formulated by a multiple emulsion technique. The Caco-2 cell monolayers were incubated with each diameter microparticles (100 g/ml) for two hours. The microparticle uptake in Caco-2 cells was studied by confocal microscopy and also by quantitating the 6-coumarin content of the microparticles taken up by the cells. The effects of microparticle concentration, and incubation time and temperature on microparticle cell uptake were also studied. Results. The study demonstrated that the Caco-2 cell microparticle uptake significantly depends upon the microparticle diameter. The 0.1 m diameter microparticles had 2.5 fold greater uptake on the weight basis than the 1 m and 6 fold greater than the 10 m diameter microparticles. Similarly in terms of number the uptake of 0.1 m diameter microparticles was 2.7 × 10³ fold greater than the 1 m and 6.7 × 10⁶ greater than the 10 m diameter microparticles. The efficiency of uptake of 0.1 m diameter microparticles at 100 g/ml concentration was 41% compared to 15% and 6% for the 1 m and the 10 m diameter microparticles, respectively. The Caco-2 cell microparticle (0.1 m) uptake increased with concentration in the range of 100 g/ml to 500 g/ml which then reached a plateau at higher concentration. The uptake of microparticles increased with incubation time, reaching a steady state at two hours. The uptake was greater at an incubation temperature of 37°C compared to at 4°C. Conclusions. The Caco-2 cell microparticle uptake was microparticle diameter, concentration, and incubation time and temperature dependent. The small diameter microparticles (0.1 m) had significantly greater uptake compared to larger diameter microparticles. The results thus suggest that the mechanism of uptake of microparticles in Caco-2 cell is particle diameter dependent. Caco-2 cells are used as an in vitro model for gastrointestinal uptake, and therefore the results obtained in these studies could be of significant importance in optimizing the microparticle-based oral drug delivery systems.     

Effect of Vehicles and Penetration Enhancers on the In Vitro and In Vivo Percutaneous Absorption of Methotrexate and Edatrexate Through Hairless Mouse Skin

Purpose. Low-dose methotrexate (MTX) is approved for the treatment of recalcitrant rheumatoid arthritis (RA). The objective of this study was to determine the effect of vehicles and penetration enhancers on the percutaneous absorption of MTX and its analog edatrexate (EDAM), and develop transdermal (TD) delivery systems of the drugs for the treatment of RA. Methods. From previously published pharmacokinetic parameters with low-dose MTX therapy, and considering a 50 cm² diffusional area, the target steady state in vitroTD flux for MTX was calculated to be 35 g/cm²/hr. Modified Franz diffusion chambers and hairless mouse skin were used for in vitro skin permeation studies. Hairless mice were used for in vivo studies. Delivered amounts of MTX and EDAM were determined by assaying the receiver phase fluid (or blood) with validated reversed phase HPLC methods. Results. Intrinsic partition coefficient of MTX was low (log P = –1.2). Target MTX fluxes of 35 g/cm²/hr were achievable only with 1–15% (v/v) Azone^® in propylene glycol (PG). Flux of EDAM (85 g/cm²/hr) was higher than MTX from an isopropyl alcohol (IPA)—5% (v/v) Azone^® system. Clinically significant steady state in vivo blood concentration of MTX and EDAM was achieved using delivery systems containing 2.5% Azone^® in PG. Area under the drug concentration-time curves (AUC_0–24hr) for MTX were 2379 and 3534 ng*hr/ml from PG—2.5% Azone^® and PG—7.5% Azone^® systems respectively. AUC_0-24hr of EDAM was 6893 ng*hr/ml using a PG—2.5% Azone^® system. Conclusions. Results of this study show the feasibility of using a transdermal delivery system of MTX and EDAM for the treatment of rheumatoid arthritis.     

Biodegradable PLGA Microspheres Loaded with Ganciclovir for Intraocular Administration. Encapsulation Technique,in Vitro Release Profiles,and Sterilization Process

Purpose. The purpose of this work was to obtain a sterilized formulation consisting of biodegradable microspheres of poly (DL-lactide-co-glycolide) (PLGA) for intraocular sustained release of ganciclovir. Methods. Microspheres were prepared using a dispersion of ganciclovir in fluorosilicone oil (FSiO) that was further dispersed in an acetone solution of PLGA [50/50 and inherent viscosity 0.41 dl/g], and emulsified in silicone oil with a surfactant. Once prepared, the formulation was exposed with an effective radiation dose of 2.5 megarads. The release rate data of ganciclovir from the sterilized and nonsterilized batches were compared using the similarity factor (f₂). Results. The dispersion of the drug in FSiO contributed to achieving a drug payload of up to 95% of the theoretical in the 300-500 m microspheres. Ten mg released ganciclovir in vitroat 1.3 g/h for the first 21 days, but decreased to 0.2 g/h from day 25 until the end of the release study (42 days). No significant differences in the amounts of encapsulated drug (=0.05) were observed between the sterilized and nonsterilized microspheres. Furthermore, dissolution profiles of formulations behaved similarly before and after gamma radiation exposure. Conclusions. The technique of microsphere preparation described resulted in high ganciclovir loading (95%) and prolonged drug release. The ganciclovir formulation behaved similarly before and after the sterilization process.     

Protein Deposition from Dry Powder Inhalers: Fine Particle Multiplets as Performance Modifiers

Purpose. To evaluate the use of carrier-based dry powder aerosols for inhalation delivery of proteins and examine the effect of fine particle excipients as potential formulation performance modifiers. Methods. Bovine serum albumin (BSA) was co-processed with malto-dextrin by spray-drying to produce model protein particles. Aerosol formulations were prepared by tumble mixing protein powders with -lactose monohydrate (63–90 m) or modified lactoses containing between 2.5 and 10% w/w fine particle lactose (FPL) or micronised polyethylene glycol 6000. Powder blends were characterised in terms of particle size distribution, morphology and powder flow. Formulation performance in Diskhaler^® and Rotahaler^® devices was investigated using a twin stage impinger operating at 60 1 min^–1. Results. Inhalation performance of binary ordered mixes prepared using BSA-maltodextrin and lactose (63–90 m) was improved by addition of FPL and micronised PEG 6000. For the addition of 5% w/w FPL the protein fine particle fraction (0.5–6.4 m) using the Diskhaler^® was increased from 31.7 ± 2.4% to 47.4 ± 2.2%. Inclusion of FPL and micronised PEG 6000 changed the bulk properties of inhalation powders and reduced powder flow but did not affect device emptying. Unexpectedly, improvements in performance were found to be independent of the order of addition of FPL to the ternary powder formulations. SEM studies revealed that this was probably the result of a redistribution of protein particles between the coarse carrier lactose component and added FPL during mixing. Conclusions. Fine particle excipients can be used to improve the performance of carrier-based protein dry powder aerosols. Mechanistically, enhancement of performance is proposed to result from a redistribution of protein particles from coarse carrier particles to the fine particle component in the ternary mix.     

Effect of prostaglandin E2 on ACTH and β-endorphin release from rat adenohypophysis in vitro after secretagogues which can mimic various first or second messengers

Summary The modulation of the depolarization induced release of [³H]-acetylcholine by agonists acting on -adrenoceptors was studied in superfused rat atrial slices. In this model, noradrenaline and methoxamine, but not UK 14304 reduced the potassium evoked release of [³H]-acetylcholine. The inhibitory action of these drugs was antagonized by the ₁ selective adrenoceptor antagonist prazosin. Propranolol, idazoxan and sulpiride did not antagonize the inhibition by noradrenaline of the potassium-evoked release of [³H]-acetylcholine. Exposure to amphetamine, -phenylethylamine, m- or p-tyramine, increased in a concentration-dependent manner the spontaneous outflow of [³H]-noradrenaline from atrial slices. Yet, these concentrations of the indirectly acting sympathomimetic amines, tested in the presence of an inhibitor of monoamine oxidase (MAO), failed to modify the potassium evoked release of [³H]-acetylcholine. Desipramine 3 mol/l or cocaine 10 mol/l did not affect the release of [³H]-acetylcholine evoked by potassium stimulation. Under similar experimental conditions, -phenylethylamine facilitated the spontaneous outflow of [³H]-noradrenaline, and inhibited the electrically-evoked release of [³H]-serotonin from the hippocampus by activation of ₂-adrenoceptors. It is concluded that the release of acetylcholine from atrial cholinergic neurons can be modulated through inhibitory ₁-adrenoceptors, which are not activated when the release of noradrenaline is induced by indirectly acting sympathomimetic amines. In addition, amphetamine or structurally related amines do not activate directly recognition sites in the cholinergic postganglionic parasympathetic neuron to modify the release of [³H-acetylcholine.     

Design and Evaluation of an Osmotic Pump Tablet (OPT) for Chlorpromazine Using (SBE)7m-β-CD

Purpose. The purpose of this study was to develop a controlled-porosity osmotic pump tablet (OPT) which exhibits pH-independent release profiles for a basic drug using a sulfobutyl ether--cyclodextrin, (SBE)_7m--CD, which acts as both a solubilizer and as an osmotic agent. Methods. Chlorpromazine free base (CLP) was chosen as a model drug for this study. The release of CLP from osmotic pump tablets was studied in vitro. In vivo absorption of CLP from the OPT was evaluated in male beagle dogs. Results. The CLP release profile from an OPT prepared from a core tablet composed of a 1:10 molar ratio of CLP to (SBE)_7m--CD was pH-independent, and was controlled by modulating the membrane thickness of the OPT. Another cyclodextrin, hydroxypropyl--cyclodextrin (HP--CD), and a sugar mixture of lactose and fructose resulted in pH-dependent release at the same molar ratio. An in vivo absorption study in dogs with an OPT containing (SBE)_7m--CD correlated very well with the in vitro release profiles using the Japanese Pharmacopoeia dissolution method. Conclusions. In addition to serving as a solubilizer and osmotic agent, (SBE)_7m--CD can also serve as the controlling agent for pH independent release of CLP from OPTs. This system successfully modified the in vivo input rate of CLP without compromising oral bioavailability.     

Oral Mucosal Permeability and Stability of Transforming Growth Factor Beta-3 In Vitro

Purpose. To investigate the permeability and localization of topically applied ¹²⁵I-TGF-3 in porcine floor-of-mouth mucosa as a function of concentration and exposure. Methods. The ¹²⁵I-TGF-3 diluted in three different vehicles was applied to the tissue samples mounted in perfusion cells maintained at 37°C. Flux and K_p values were calculated from the perfusate collected over a 24 hour period. The quantity of ¹²⁵I-TGF-3 present in the tissue was determined by horizontal sectioning and subsequent counting. The stability of ¹²⁵I-TGF-3 in saliva and in the tissue was analyzed by SDS polyacrylamide gradient gel electrophoresis. Results. ¹²⁵I-TGF-3 was relatively stable in saliva and in the epithelium; approximately 50% of the total counts in the deeper epithelium were resident in the 25kDa TGF-3 homodimer. A steady-state flux was reached 6 hours post application and K_p value was 4.0 ± 0.6 × 10^-6 (mean ± sem). Penetration of ¹²⁵I-TGF-3 to the basal cell layer was concentration dependent but reached nanomolar concentrations even after extensive surface rinsing, representing over one-thousand fold the IC₅₀ for epithelial cell cycle arrest. Conclusions. The data suggest that topical application of TGF-3 to the oral mucosa in an appropriate vehicle can provide effective therapeutic delivery to the tissue.     

Arsenic dose in patients with cutaneous carcinomata and hepatic haemangio-endothelioma after environmental and occupational exposure

A total of 16 male cases with malignant tumours associated with arsenic-polluted water were observed in Tarapacá and Antofagasta Provinces, northern Chile. Fifteen of them had skin carcinomata and the remaining one a haemangio-endothelioma of liver. The 15 skin cancer cases had latent periods ranging from 12–45 years. Three patients were studied in detail. The first one (skin cancer) had a latent period of 20 years with a weighted mean dose of 1.2 mg/day (total dose for latent period 8.4 g). The second one (skin cancer) had a latent period of 23 years with a weighted mean dose of 1.0 mg/day (total dose for latent period 8.3 g). The third case (liver tumour) exhibited a latent period of 14 years with a weighted mean of 0.6 mg/day (total dose for latent period 3.1 g).Fifteen of the 16 cancer patients were labourers. For normal subjects of different ages and both sexes (n=290) and ingesting arsenic-polluted water (0.60 ppm), the relationship between mean age and mean arsenic dose is expressed by a weighted least square polynomial regression, of second degree: (y) = _o + ₁ ^t + ₂ ^{t 2} where y is mean arsenic dose (mg/person/day) and t is mean age (years). For the general male population and for male labourers, the respective equations are presented.Deceased. National Academy of Medicine, Santiago, Chile     

Intracranial Delivery of Recombinant Nerve Growth Factor: Release Kinetics and Protein Distribution for Three Delivery Systems

Purpose. Three different polymeric delivery systems, composed of either poly(ethylene-co-vinyl acetate) (EVAc) or poly(lactide-co-gly-colide) (PLGA), were used to administer recombinant human nerve growth factor (rhNGF) intracranially in rats. Methods. The delivery systems were characterized with respect to release kinetics, both in the brain and in well-stirred buffer solutions. Results. During incubation in buffered saline, the delivery systems released rhNGF in distinct patterns: sustained (EVAc), immediate (PLGA₁), and delayed (PLGA₂). One 10-mg delivery system was implanted in each rat and an ELISA technique was used to determine the amount of rhNGF in 1-mm coronal brain slices produced immediately after removal of the delivery system. High levels of rhNGF (as high as 60,000 ng in a brain slice of 50 L) were recovered from the brain tissue at 1,2, and 4 weeks after implantation. With all three delivery systems, the amount of rhNGF in each brain slice decreased exponentially with distance from the implant site; the distance over which concentration decreased by 10-fold was 2–3 mm for all delivery systems. When rhNGF release was moderate (10 to 200 ng rhNGF/ day), the total amount of rhNGF in the brain increased linearly with release rate, suggesting an overall rate of rhNGF elimination of 0.4 hr^–1 or a half-life of 1.7 hr. With higher release rates (500 to 50,000 ng rhNGF/day), total amounts of rhNGF in the brain were considerably higher than anticipated based on this rate of elimination. Conclusions. Polymeric controlled release can provide high, localized doses of rhNGF in the brain. All of the experimental data were consistent with penetration of rhNGF through the brain tissue with a diffusion coefficient 8 X 10^–7 cm²/s, which is 50% of the diffusion coefficient in water.     

Comparison of the antagonistic activity of tamsulosin and doxazosin at vascular α1-adrenoceptors in humans

₁-Adrenoceptor blockers such as prazosin and doxazosin are used to treat hypertension as well as benign prostatic hyperplasia (BPH), whereas the new _l-adrenoceptor blocker tamsulosin is used only for BPH and does not reduce blood pressure at the doses used to relax prostatic smooth muscle. In contrast to prazosin, tamsulosin has a higher affinity for prostatic than vascular ₁-adrenoceptors in vitro. The functional correlate of this observation in humans is the subject of this study. The ₁-adrenoceptor blockade by oral tamsulosin (0.2 mg), doxazosin (1 mg) or placebo on finger tip vascular and dorsal hand venous ₁-adrenoceptors stimulated by cold treatment (immersion in ice water) and the _l-adrenoceptor agonist phenylephrine, was thus studied in a 3-way crossover study in eight, healthy, male adults. Finger tip vasoconstriction after cold stimulation was assessed by laser Doppler flowmetry. A linear variable differential transformer was used to assess the drug effect on phenylephrine-induced venoconstriction. All study parameters were assessed at around 2 and 3.5 h after oral intake of doxazosin and tamsulosin respectively. The drug plasma levels were not significantly different. No significant differences were found for blood pressure or heart rate in the three treatments in supine and erect position. The reduction in finger tip blood flow after cold stimulation was significantly smaller after doxazosin treatment (P<0.01) than after tamsulosin or placebo, whereas there was no significant difference between tamsulosin and placebo treatments. The infusion rate of phenylephrine producing a half-maximum venoconstriction was significantly larger after doxazosin than after tamsulosin (P<0.05) or placebo (P<0.01), whereas there was again no significant difference between tamsulosin and placebo treatments. The data suggest that, at doses producing equal plasma levels after single oral doses in human subjects, the blocking activity at vascular ₁-adrenoceptors is lower for tamsulosin than for doxazosin.     

A New Mathematical Model Quantifying Drug Release from Bioerodible Microparticles Using Monte Carlo Simulations

Purpose. The major objectives of this study were to 1) develop a new mathematical model describing all phases of drug release from bioerodible microparticles; 2) evaluate the validity of the theory with experimental data; and 3) use the model to elucidate the release mechanisms in poly(lactide-co-glycolide acid)-based microspheres. Methods. 5-Fluorouracil-loaded microparticles were prepared with an oil-in-water solvent extraction technique and characterized in vitro. Monte Carlo simulations and sets of partial differential equations were used to describe the occurring chemical reactions and physical mass transport phenomena during drug release. Results. The new mathematical model considers drug dissolution, diffusion with nonconstant diffusivities and moving boundary conditions, polymer degradation/erosion, time-dependent system porosities, and the three-dimensional geometry of the devices. In contrast with previous theories, this model is able to describe the observed drug release kinetics accurately over the entire period of time, including 1) initial burst effects; 2) subsequent, approximately zero-order drug release phases; and 3) second rapid drug release phases. Important information, such as the evolution of the drug concentration profiles within the microparticles, can be calculated. Conclusions. A new, mechanistic mathematical model was developed that allows further insight into the release mechanisms in bioerodible microparticles.     

Thermodynamics of Solutions I: Benzoic Acid and Acetylsalicylic Acid as Models for Drug Substances and the Prediction of Solubility

Purpose. To investigate the solution process of drug substances (exemplified by benzoic acid, BA, and acetylsalicylic acid, ASA), particularly the interrelation between enthalpic and entropic terms of Gibbs energy, in different solvents. To develop an approach for the estimation of standard solution enthalpies based on a self-consistent thermochemical scale. Method. Two independent methods, solubility experiments (concentrations of saturated solutions) and solution calorimetry (standard solution enthalpies) in aliphatic alcohols and individual organic solvents were used. Correlation between the thermodynamic functions in various solvents were analyzed by standard statistical methods. Multiple regression analysis between H ⁰ _sol values and the parameters of the solvents was run on the Koppel-Palm equation. Results. Based on experimental data, a compensation effect between thermodynamic functions was observed. Correlation was found between H ⁰ _sol (BA) and H ⁰ _sol (ASA) [where the H ⁰ _sol (BA)-values were used as a self-consistent thermochemical scale]. Furthermore, H ⁰ _sol correlated with the Koppel-Palm basicity of the solvents. Conclusions. The model based on solubility and solution experiments might be useful for the prediction of solubility or solvation of drug substances in different media. The regression equation based on the self-consistent thermochemical scale makes it possible to approximate the ability to solvate a drug substance in comparison with structure-relative substances.     

A kinetic study of the release of noradrenaline by tyramine

Summary Dog saphenous vein strips obtained from untreated or reserpine-pretreated animals were incubated with 1,4 mol/l ³H-(–)noradrenaline for 60 min after inhibition of the noradrenaline-metabolizing enzymes and of extraneuronal uptake. At the end of the incubation period the strips were perifused during 200 min. Some strips were exposed to tyramine from the 100th to the 200th min of perifusion. A compartment analysis of spontaneous or tyramine-induced efflux of ³H-noradrenaline was made. The spontaneous efflux of strips obtained from untreated animals had a long half time (t/2=269 min), and most of the ³H-noradrenaline which accumulated in the strips did not participate in the efflux (bound fraction, representing 85% of tissue activity at the 100th min of perifusion). The strips were exposed to five concentrations of tyramine, ranging from 0.49–3,240 mol/l. At all concentrations, tyramine mobilized only one noradrenaline compartment. The increase of tyramine concentration decreased the bound fraction, which became negligible for the highest concentration of tyramine. The half time of ³H-efflux induced by tyramine decreased from 278–106 min when the tyramine concentration was increased from 0.49–40 mol/l. However, further increases of the concentration of tyramine up to 3240 mol/l did not result in a significantly lower half time.Strips obtained from reserpine-pretreated animals were characterized by a low accumulation of ³H-noradrenaline (403 ng/g vs. 1,374 ng/g for strips obtained from unpretreated animals, at the 100th min of perifusion), the efflux had a half time of only 122 min and the bound fraction was smaller than in strips obtained from unpretreated animals (bound fraction representing 47% of tissue activity at the 100th min of perifusion). Reserpine-pretreated strips were exposed to 40 mol/l tyramine. Under these experimental conditions there was no significant bound fraction. The ³H-efflux induced by tyramine decayed according to a two-compartment model, with half times of 8 and 50 min.The results support the view that in preparations from unpretreated animals the size of the noradrenaline pool available for release by tyramine is dependent on the concentration of the latter amine. Furthermore, the half time of the efflux evoked by tyramine in strips with intact vesicular stores is dependent on a rate-limiting process, probably of vesicular location.Results presented to the 4th Meeting on Adrenergic Mechanisms (Porto 1980). This work was supported by a grant from Instituto Nacional de Investigação Cientifica (Centro de Farmacologia e Biopatologia Química da Universidade do Porto)     

Protein Aggregates Seem to Play a Key Role Among the Parameters Influencing the Antigenicity of Interferon Alpha (IFN-α) in Normal and Transgenic Mice

Purpose. During long-term treatment of various malignant or viral diseases with IFN- up to 20% of patients develop anti-IFN- antibodies for as yet unknown reasons. Methods. To address this issue, a mouse model using Balb/C mice was established and the relevance of several potentially anti-IFN- antibodies inducing factors was studied. Results. The model revealed that both a higher frequency of injections and a higher dosage of IFN- were more immunogenic and that the route of administration affected the antibody response to IFN-. The intrinsic immunostimulatory activity of IFN- itself also enhanced the immune response. IFN- protein aggregates (IFN--IFN- and human serum albumin (HSA)-IFN- aggregates), which were recently identified in all marketed IFN- products, were significantly more immunogenic than IFN- monomers. These aggregates broke the tolerance against human IFN- monomers in human IFN- transgenic mice. Conclusions. Based on these animal studies it is proposed that the immune response to IFN- in humans is most probably elicited by a combination of several factors among which IFN- protein aggregates seem to play a key role.     

In Vitro Cutaneous Disposition of a Topical Diclofenac Lotion in Human Skin: Effect of a Multi-Dose Regimen

Purpose. This study determines comparative bioavailability of diclofenac sodium lotion compared to an aqueous solution after topical application to viable human skin in vitro. In addition, the difference between a single dose and multiple doses (8 times) was also determined. Methods. An in vitro flow-through diffusion cell system was employed, using radiolabelled diclofenac sodium. Results. Multiple doses of lotion (2 l/cm² and 5 l/cm²) delivered a total of 40.1 ± 17.6 g and 85.6 ± 41.4 g diclofenac, respectively, at 48 h, compared to only 9.4 ± 2.9 g and 35.7 ± 19.0 g absorbed after topical application of diclofenac as an aqueous solution (P < 0.05). A single dose study showed no statistical difference between diclofenac delivered in lotion or an aqueous solution. Over 48 h the total absorption from lotion was 10.2 ± 6.7 g and 26.2 ± 17.6 g (2 l/cm² and 5 l/cm², respectively), compared to 8.3 ± 1.5 g and 12.5 ± 5.7 g from an aqueous solution. Both single doses of lotion and aqueous diclofenac showed decreased diclofenac absorption into the receptor fluid between 12 and 24 h. However, when applied multiple times, absorption from lotion was continually increasing up to 48 h. The total dose accountability ranged from 76.8 ± 8.2% to 110.6 ± 15.1% of the applied dose. Conclusions. Diclofenac lotion exhibited enhanced diclofenac percutaneous absorption rate through human skin (mass, flux and partition coefficient) when applied a multiple number of times and this enhanced absorption was maintained over 48 h. This suggests that a constituent of the lotion (DMSO) will enhance human skin absorption of diclofenac when used in a multi-dose regimen, but not after a single dose.     

Influence of Particle Size,Air Flow,and Inhaler Device on the Dispersion of Mannitol Powders as Aerosols

Purpose. To study the effect of particle size, air flow and inhaler type on the dispersion of spray dried mannitol powders into aerosols. Methods. Mannitol powders were prepared by spray drying. The solid state properties of the powders were determined by laser diffraction, X-ray powder diffraction, scanning electron microscopy, freeze fracture, Karl Fischer titration and gas pycnometry. The powders were dispersed using Rotahaler^® and Dinkihaler^®, connected to a multistage liquid impinger at different air flows. Results. Three crystalline mannitol powders with primary particle size (MMD) 2.7, 5.0, 7.3 m and a similar polydispersity were obtained. The particles were spherical with a density of 1.5 g/cm³ and a moisture content of 0.4 wt.%. At an air flow of 30 L/min all the powders were poorly dispersed by both inhalers. With the Rotahaler^® increasing the flow (60–120 L/min) increased the fine particle fraction (FPF) in the aerosols for the 2.7 m powder, and decreased the FPF for the 7.3 m powder; whereas the FPF for 5.0 m powder was unaffected. With the Dinkihaler^®, all the powders were near complete dispersion at 60 L/min. Conclusions. The FPF in the mannitol powder aerosols was determined by an interplay of the particle size, air flow and inhaler design.