Polyacrylate resin microcapsules for taste masking of antibiotics.

Various microencapsulated dosage forms were prepared to limit the release of an antibiotic in solution for up to 3 days and in the oral cavity following per oral administration. An experimental antibiotic, clarithromycin (TE-031), was used in these studies. The drug was first encapsulated in gelatin followed in some cases by crosslinking with glutaraldehyde. The gelatin microcapsules were then coated with acrylic resins (Eudragit), whose solubility properties vary according to pH. A non-solvent coacervation technique was used to apply the Eudragit resins. It was found that crosslinking the gelatin retarded release of TE-031 somewhat relative to that from uncrosslinked gelatin microcapsules in a 72h release experiment conducted at room temperature. Coating the gelatin microcapsules with Eudragit resins L100, S100, or E100 slowed the release of TE-031 further still; less TE-031 was released over 72 h from the Eudragit-coated formulations prepared with crosslinked gelatin compared with formulations prepared with uncrosslinked gelatin. The Eudragit E100-coated crosslinked gelatin microcapsule formulation was most effective in preventing release of the TE-031 under simulated conditions of storage in an aqueous solution.     

Deconvolution analysis for absorption and metabolism of aspirin in microcapsules

We have previously proposed a novel deconvolution method, which can estimate first-pass metabolism of orally administered drugs. In the present study, we examined whether this deconvolution method is useful for evaluating oral dosage forms. The absorption and first-pass metabolism of orally administered aspirin formulated in several forms were analyzed. Two types of microcapsules consisting of Eudragit L100 alone and Eudragit L100/ethylcellulose (4:6) were prepared as sustained release formulations, for comparison with aspirin in powder form. The deconvolution analysis revealed that absorption of aspirin was sustained by encapsulating it in microcapsules. Interestingly, it also revealed that the percentage metabolized during absorption was different among the three types of formulations. Thus, the deconvolution method has enabled a comprehensive analysis of orally administered drugs. This method is believed to contribute to the evaluation of oral drug formulations.     

Preparation and in vitro evaluation of slow release ketoprofen microcapsules formulated into tablets and capsules

Abstract

Ketoprofen powder was encapsulated with Eudragit RL/RS polymer solutions in isopropanol-acetone 1:1, using a simple and rapid method. Microcapsules were prepared using Eudragit solutions with different RL/RS ratios. The encapsulation process produces free-flowing microcapsules with good drug content and marked decrease in dissolution rate. The retardation in release profile of ketoprofen from microcapsules was a function of the polymer ratio employed in the encapsulation process. In vitro release of ketoprofen from microcapsules either filled in gelatin capsules or compressed into tablets, using calcium sulphate as diluent, confirmed the efficiency of the encapsulation process for preparing prolonged release medication. A capsule formulation with optimum sustained-release profile was suggested.     

Technology to obtain sustained release characteristics of drugs after delivered to the colon

To determine the necessary technology by which sustained drug release is obtained after drug is delivered to the colon, two kinds of microcapsules were prepared and were filled in a pressure-controlled colon delivery capsule (PCDC). As a model drug 5-aminosalicylic acid (5-ASA) was used, because the target site of 5-ASA is the entire large intestine. 5-ASA was microencapsulated using a water-insoluble polymer, ethylcellulose (EC) or with pH-sensitive polymers, Eudragit L-100 or S-100 and encased in PCDC. The particle size of these microcapsules was around 800 microns and the loading efficiencies of 5-ASA were approximately 90%. In vitro dissolution tests were performed with the prepared microcapsules. The release rate of 5-ASA from the microcapsules was significantly prolonged as compared to 5-ASA powder, although there were no significant differences in the release rates between these microcapsules. By incorporating the 5-ASA microcapsules into PCDC, sustained release PCDCs for colon delivery were prepared and in vivo evaluation was performed using beagle dogs. As a fast release colon delivery system, PCDCs were prepared with 5-ASA powder suspended in suppository base. After oral administration of the test preparations to beagle dogs, plasma 5-ASA concentrations were measured and sustained release characteristics of 5-ASA from the test preparations were evaluated from the plasma 5-ASA concentration-time profiles. The first appearance time of 5-ASA into the systemic circulation after oral administration were 3 h for all the colon delivery preparations and it was thought that these test preparations were delivered to the colon. Both EC microcapsules and Eudragit S-100/RS-100 microcapsules in PCDC showed longer the mean residence time MRT, 8.2 +/- 0.6 h and 8.7 +/- 0.9 h, than Eudragit L-100/RS-100 microcapsules in PCDC where the MRT was 6.6 +/- 0.2 h. Since PCDCs containing 5-ASA powder exhibited a MRT of 7.0 +/- 1.0 h, these two types of preparations have suggested sustained release characteristics.     

Collagen-poly (HEMA) hydrogels for the controlled delivery of methotrexate and cisplatin

Collagen-poly (HEMA) hydrogels containing methotrexate (HGM) and cisplatin (HGC) were prepared and characterised for their drug content. The in vitro release profiles of surface crosslinked HGM (S-HGM), and deeper crosslinked HGM (D-HGM) were studied in phosphate buffer at pH 6.8 and 7.4 and compared with those of uncrosslinked HGM (U-HGM), and uncrosslinked HGC (U-HGC). All types of hydrogels showed controlled and near zero order release of the two anticancer drugs. Crosslinked HGM released MTX at a slower rate than uncrosslinked HGM. Between the two types of crosslinking studied, surface crosslinked hydrogels showed a faster release rate than deeper crosslinked HGM.     

Preparation and in vitro evaluation of slow release ketoprofen microcapsules formulated into tablets and capsules.

Ketoprofen powder was encapsulated with Eudragit RL/RS polymer solutions in isopropanol-acetone 1:1, using a simple and rapid method. Microcapsules were prepared using Eudragit solutions with different RL/RS ratios. The encapsulation process produces free-flowing microcapsules with good drug content and marked decrease in dissolution rate. The retardation in release profile of ketoprofen from microcapsules was a function of the polymer ratio employed in the encapsulation process. In vitro release of ketoprofen from microcapsules either filled in gelatin capsules or compressed into tablets, using calcium sulphate as diluent, confirmed the efficiency of the encapsulation process for preparing prolonged release medication. A capsule formulation with optimum sustained-release profile was suggested.     

Salmon calcitonin-loaded Eudragit® and Eudragit®-PLGA nanoparticles: in vitro and in vivo evaluation

The main objective of this study was to prepare salmon calcitonin (sCT)-loaded Eudragit?RSPO, Eudragit?L100 and Eudragit?-poly(lactic-co-glycolic acid) blend nanoparticles for in vitro and in vivo evaluation as an oral drug delivery system. The prepared nanoparticles ranged in size from 179.7 to 308.9?nm with a polydispersity index between 0.051 and 2.75, and had surface charges ~ -11 to +6?mV. Efficient sCT encapsulation and release was observed with all the nanoparticle formulations. The polymer type was an important factor that influenced the release characteristics and the in vivo hypocalcemic effect. Nanoparticle formulations were also prepared with sodium taurodeoxycholate (NaTDC) and characterized. No statistically significant difference was noted between the hypocalcemic effect of any of the nanoparticle formulations with and without NaTDC (p?>?0.05). The use of Eudragit?RSPO nanoparticles appears to be a potential approach for the oral delivery of sCT.     

Dissolution stability studies of suspensions of prolonged-release diclofenac microcapsules prepared by the Wurster process: I. Eudragit-based formulation and possible drug-excipient interaction

The aim was to evaluate possible interaction in solid and liquid state of the drug with formulation excipients consequent to very fast drug release of diclofenac-Eudragit prolonged release microcapsules. The microcapsules were prepared by drug layering on calcium carbonate cores and coated with Eudragit RS 30D and L30D-55 as previously reported. Suspension of the microcapsules was prepared using microcrystalline cellulose/sodium carboxymethyl cellulose (Avicel CL-611) as medium. In vitro dissolution testing of the suspension was done, and, based on the dissolution results, possible interaction between diclofenac and Eudragit and Avicel in the medium was studied. Powder X-ray diffraction (PXRD) and differential scanning calorimetry (DSC) analyses were performed using 1:1 binary, 1:1:1 ternary mixtures and a ratio equivalent to that in the formulation. The mixtures were prepared by mixing the dispersions--Eudragit RS 30D or L30D-55 with the drug or other components, followed by drying at 60 degrees C for 48 h. Dry mixing was done using the powder equivalents of the polymers, Eudragit RS PO and L100-55, Avicel and calcium carbonate. In vitro dissolution of the suspended microcapsules showed a very fast release after 48 h (T50 = <1 h) compared to the solid microcapsules (T50 = 6 h). DSC curves of the formulation components or microcapsules did not show the characteristic endothermic peak of diclofenac at 287 degrees C. Powder X-ray diffraction of the binary or ternary mixtures of diclofenac and Eudragit polymers indicated reduction, shift or modification of the crystalline peaks of the drug or excipients at 2theta of 12 degrees and 18 degrees , suggestive of interaction. Some changes in drug peak characteristics at 18 degrees and 23 degrees were observed for Avicel/drug mixture, though not significant. The DSC curves of the binary mixture of diclofenac co-dried with liquid forms of Eudragit (i.e. RS 30D or L30D-55) revealed greater interaction compared to the curves of drug and powdered forms of Eudragit (RS PO or L100-55). This was depicted by greater shift in fusion points of the mixtures relative to the drug. However, comparing the RS and L-type Eudragit, the latter generally showed greater interaction with the drug. Interaction between diclofenac and L-type Eudragit polymers can occur in liquid formulations.     

Chemical and Swelling Evaluations of Amino Group Crosslinking in Gelatin and Modified Gelatin Matrices

Purpose. To determine the extent of amino group crosslinking in gelatin matrices by chemical assay, and to compare these results to crosslinking evaluations from swelling measurements. Methods. Matrices crosslinked with a water soluble carbodiimide (EDC/G), glutaraldehyde (GTA/G), as well as a GTA crosslinked matrix prepared from gelatin modified to contain 230% greater crosslinking sites (GTA/Mod) were evaluated. Crosslinking extent, X _c, was determined by a UV assay of uncrosslinked amino groups before and after crosslinking, and was used to obtain crosslinking densities. Equilibrium swelling ratios, Q _m at 37°C in isotonic pH 7.4 were used to calculate crosslinking degree from the Flory equation for swelling of ionic polymers for comparison to the chemically determined crosslinking densities. Results. Of the original 33 × 10^–5 moles -amino groups/g gelatin, 91 to 95% were crosslinked in EDC/G and GTA/G. GTA/Mod lost 95% of the original 108 × 10^–5 moles amino groups/g gelatin. Crosslinking densities were 4.1 × 10^–4 and 4.2 × 10^–4 moles/mL for EDC/G and GTA/G, respectively. The value for GTA/Mod increased to 14.2 × 10^–4 moles/mL. Values of Q _m followed the same trend. The Flory crosslinking degrees for both gelatin matrices were 12 × 10^–4 and 13 × 10^–4 moles/mL, respectively. The value for the more extensively crosslinked GTA/Mod was 280 × 10^–4moles/mL. Conclusions. The swelling and chemical evaluations of crosslinking are in general agreement for matrices with the lower of two crosslinking levels. The chemical determination appears suitable for evaluating amino group crosslinking in gelatin and it may be suitable for other proteinaceous materials.     

Pharmacokinetics of clarithromycin granule and tablet in children

It has been known that clarithromycin (TE-031, A-56268), a new macrolide antibiotic (ML), achieves higher concentrations in blood, is better excreted into urine and is better distributed into various tissues than conventional MLs. We investigated the pharmacokinetics of TE-031 in children upon oral administration of the drug in the following method. TE-031 granular preparation with a potency of 100 mg/g was given to 6 boys (5 years 4 months-14 years 0 month) with dose levels of 5 mg/kg and 10 mg/kg for each 3 boys. A tablet preparation with each tablet containing 50 mg of TE-031 was administered to 4 boys and 2 girls (8 years 5 months-11 years 6 months) with dose level of 2 tablets (i.e., 100 mg) and 3 tablets (i.e., 150 mg) for each 3 children. All administrations were done at 30 minutes before meal. Then, to conduct a cross-over test, the granule preparation was given orally to the 3 children mentioned above who was given 2 tablets and the 1 of 3 cases that were given 3 tablets at the same dose levels (100 mg and 150 mg) respectively. A bioassay was used to determine concentrations in blood of active antibiotic compounds and an high performance liquid chromatography (HPLC) was used to determine unchanged TE-031 and its main metabolite, M-5. Urinary concentrations of active antibiotic compounds were also determined by the bioassay and the HPLC was used to determine concentrations and proportions of unchanged TE-031 and its metabolites, M-1, M-4, M-5, M-6 and M-7 to figure out the urinary recovery rate in the first 6 hours. The results of these experiments are summarized as follows. 1. As was mentioned above, TE-031 was administered orally to 2 groups of children at dose levels of 5 mg/kg and 10 mg/kg, respectively. Mean serum levels of total active antibiotic compounds reached their maximum in 1 and 2 hours for the 5 mg/kg and the 10 mg/kg dosage groups, respectively, at 1.28 and 3.62 micrograms/ml, respectively. Mean half lives of serum concentrations in the 2 groups were quite similar, with values of at 2.1 and 2.0 hours, respectively. Mean serum concentrations of unchanged TE-031 determined by the HPLC method reached their peaks in 1 hour after administration in either of the 5 and 10 mg/kg dosage groups at peak levels of 0.65 micrograms/ml and 2.67 micrograms/ml, respectively. Thus, dose-response relationships were observed with TE-031 and M-5.(ABSTRACT TRUNCATED AT 400 WORDS)     

Design of prolonged-release microcapsules containing diclofenac sodium for oral suspensions and their preparation by the Wurster process

Prolonged-release microcapsules of diclofenac sodium (DS), an acidic drug, applicable as an oral suspension for twice-a-day administration were designed. The microcapsules with a mass median diameter of around 100 μm and a high drug content were intended to exhibit a preferably prolonged release of highly water-soluble DS when prepared by the Wurster process–a spray coating method using a spouted bed assisted with a draft tube. The microcapsule was composed of a calcium carbonate core of 32–44 μm, a drug-layer of DS, hydroxypropyl cellulose and polyethyleneglycol 6000, an undercoat of Eudragit L30D and a release-sustaining coat of Eudragit RS30D. Eudragit L30D films were undercoated to decrease the solubility of DS within the environment of the microcapsules and thereby to prolong the drug release. This made it possible to decrease the amount of Eudragit RS30D membrane required to prolong the drug release, leading to decrease in the particle size of products and achievement of high drug content. As a result, prolonged release microcapsules with a mass median diameter of 92 μm and a drug content of 29% could be obtained.     

Time and pH dependent colon specific, pulsatile delivery of theophylline for nocturnal asthma

In this study, investigation of an oral colon specific, pulsatile device to achieve time and/or site specific release of theophylline, based on chronopharmaceutical consideration. The basic design consists of an insoluble hard gelatin capsule body, filled with eudragit microcapsules of theophylline and sealed with a hydrogel plug. The entire device was enteric coated, so that the variability in gastric emptying time can be overcome and a colon-specific release can be achieved. The theophylline microcapsules were prepared in four batches, with Eudragit L-100 and S-100 (1:2) by varying drug to polymer ratio and evaluated for the particle size, drug content and in vitro release profile and from the obtained results; one better formulation was selected for further fabrication of pulsatile capsule. Different hydrogel polymers were used as plugs, to maintain a suitable lag period and it was found that the drug release was controlled by the proportion of polymers used. In vitro release studies of pulsatile device revealed that, increasing the hydrophilic polymer content resulted in delayed release of theophylline from microcapsules. The gamma scintigraphic study pointed out the capability of the system to release drug in lower parts of GIT after a programmed lag time for nocturnal asthma. Programmable pulsatile, colon-specific release has been achieved from a capsule device over a 2-24h period, consistent with the demands of chronotherapeutic drug delivery.     

Microencapsulation of beta-galactosidase with Eudragit L-100

Microcapsules containing beta-galactosidase (lactase) were prepared by solvent evaporation using the pH sensitive polymer, Eudragit L-100. Formulations were prepared using various polymer-enzyme ratios with total solids content of the internal phase using sucrose stearate as a droplet stabilizer. Particle size distributions were invariant to relative proportion of ingredients but were dependent on stirring conditions. Although sucrose stearate had no effect on particle size distribution, release rate or encapsulation efficiency, its presence at a minimum 2% level was necessary to ensure intact microcapsules. Encapsulation efficiencies were higher for formulations prepared with 15% compared to 10% total solid content. DSC results revealed an interaction between encapsulated Eudragit L-100-enzyme-sucrose stearate vs their physical mixtures. The enzyme activities of the freshly prepared product vs those stored under stressed condition (40 degrees C and 75% RH) were 68 and 40% of their pre-processing activity, respectively. In vitro dissolution showed no enzyme release at 1 h in acidic media but 80% of the lactase was released from the microcapsules over 2.5 h in pH 6.8 media, thus establishing the feasibility of lactase microencapsulation to retard enzyme release in an acidic environment and ensuring release at intestinal pH.     

Preparation of polylactide-co-glycolide and chitosan hybrid microcapsules of amifostine using coaxial ultrasonic atomizer with solvent evaporation

The objective of this study was to evaluate the effect of various processing and formulation factors on the characteristics of amifostine hybrid microcapsules. Amifostine-loaded hybrid microcapsules were prepared using PLGA and chitosan. In short, amifostine powder was dissolved in de-aerated water with or without chitosan. The amifostine solution was later emulsified into PLGA solution in dichloromethane containing phosphatidylcholine. The resultant emulsion was fed through the inner capillary of a coaxial ultrasonic atomizer. The liquid fed through the coaxial outer capillary was either water or chitosan solution. The atomized droplets were collected into PVA solution and the droplets formed microcapsules immediately. The hybrid microcapsules prepared with chitosan solution only as an outer layer liquid showed the maximum efficiency of encapsulation (30%). The median sizes of all three formulations were 33-44 microm. These formulations with chitosan showed positive zeta-potential and sustained drug release with 13-45% amifostine released in 24 h. When chitosan was incorporated into inner as well as outer liquid layers, the drug release increased significantly, 45% (compared with other formulations) released in 24 h and almost 100% released in 11 days. Hybrid microcapsules of amifostine showed moderately high efficiency of encapsulation. The cationic charge (due to the presence of chitosan) of these particles is expected to favour oral absorption and thus overall bioavailability of orally administered amifostine.     

Dissolution stability studies of suspensions of prolonged-release diclofenac microcapsules prepared by the Wurster process: I. Eudragit-based formulation and possible drug-excipient interaction

The aim was to evaluate possible interaction in solid and liquid state of the drug with formulation excipients consequent to very fast drug release of diclofenac-Eudragit® prolonged release microcapsules. The microcapsules were prepared by drug layering on calcium carbonate cores and coated with Eudragit® RS 30D and L30D-55 as previously reported. Suspension of the microcapsules was prepared using microcrystalline cellulose/sodium carboxymethyl cellulose (Avicel® CL-611) as medium. In vitro dissolution testing of the suspension was done, and, based on the dissolution results, possible interaction between diclofenac and Eudragit and Avicel in the medium was studied. Powder X-ray diffraction (PXRD) and differential scanning calorimetry (DSC) analyses were performed using 1:1 binary, 1:1:1 ternary mixtures and a ratio equivalent to that in the formulation. The mixtures were prepared by mixing the dispersions—Eudragit RS 30D or L30D-55 with the drug or other components, followed by drying at 60°C for 48?h. Dry mixing was done using the powder equivalents of the polymers, Eudragit RS PO and L100-55, Avicel and calcium carbonate. In vitro dissolution of the suspended microcapsules showed a very fast release after 48?h (T₅₀?=?<1?h) compared to the solid microcapsules (T₅₀?=?6?h). DSC curves of the formulation components or microcapsules did not show the characteristic endothermic peak of diclofenac at 287°C. Powder X-ray diffraction of the binary or ternary mixtures of diclofenac and Eudragit polymers indicated reduction, shift or modification of the crystalline peaks of the drug or excipients at 2θ of 12° and 18°, suggestive of interaction. Some changes in drug peak characteristics at 18° and 23° were observed for Avicel/drug mixture, though not significant. The DSC curves of the binary mixture of diclofenac co-dried with liquid forms of Eudragit (i.e. RS 30D or L30D-55) revealed greater interaction compared to the curves of drug and powdered forms of Eudragit (RS PO or L100-55). This was depicted by greater shift in fusion points of the mixtures relative to the drug. However, comparing the RS and L-type Eudragit, the latter generally showed greater interaction with the drug. Interaction between diclofenac and L-type Eudragit polymers can occur in liquid formulations.     

Release of diltiazem from Eudragit microparticles prepared by spray-drying

Microparticles containing diltiazem hydrochloride were prepared by the spray-drying technique using acrylatemethacrylate copolymers, Eudragit RS and Eudragit RL, as coating materials. The choice of solvent used during spray-drying determined the structure of the resultant microparticles. Spray-drying using dichloromethane as the solvent resulted in microspheres where the drug was distributed in the coating polymer matrix, whereas using toluene gave microcapsules with the drug coated by the polymer. The particle size distribution for both microspheres and microcapsules was narrow, with mean particle size below 10 μm. DTA-analysis showed that the drug was amorphous in the microspheres but crystalline in the microcapsules. The release pattern of diltiazem hydrochloride was affected by microparticle structure, whether the structure was matrix (microspheres) or reservoir (microcapsules). The results indicate that spray-drying is a method that can be used to prepare microparticles from the Eudragit acrylic resins RL and RS with a narrow particle size distribution. It is concluded that drug release rate can be controlled by choice of polymer type and production conditions during spray-drying.     

Preparation and evaluation of slow-release pan-coated indomethacin granules

Abstract

Granules containing indomethacin crystals are coated with Eudragit solutions of different RL/RS ratios using a pan coating technique. The process is reproducible with regard to drug content, inexpensive and the formed granules were directly compressed into tablets. In vitro release of indomethacin from coated granules, tablets and capsules was studied as a function of different ratios of Eudragit RL/RS in the coating solution. The release of the drug was significantly reduced by the coating process in comparison with a formulation made from uncoated granules, prepared using 10 per cent gelatin solution as a binder. Release data were found to follow a diffusion-controlled model.     

Clinical evaluation of clarithromycin in pediatric patients

A clinical evaluation of clarithromycin (TE-031, A-56268), a newly synthesized macrolide antibiotic, was made for its efficacy and safety in 30 patients with ages ranging from 8 month-old to 12 year- 2 month-old with mycoplasmal and bacterial infections. The obtained results are summarized below. 1. A pharmacokinetic study following oral administration of TE-031 at 10 mg/kg (granule) or 5.5 mg/kg (tablet) resulted in blood concentrations and urinary recovery rates higher than with other macrolides. 2. TE-031 was administered orally to 5 patients with Mycoplasma pneumonia, 21 patients with pneumonia or bronchopneumonia, 2 patients with pertussis and 2 patients with enterocolitis at daily dosages ranging 11.1-31.6 mg/kg divided into 3. Clinical evaluations of these 30 patients were as follows; excellent: 19 patients, good: 11 patients. The efficacy rate was 100%. 3. Neither clinical adverse reaction nor abnormal laboratory data was found in any of these 30 patients. 4. MICs of TE-031 against 10 strains of bacteria isolated from 10 patients with pneumonia or bronchopneumonia were as follows. MICs against 3, 2 and 2 out of 7 strains of Streptococcus pneumoniae were less than 0.025 microgram/ml, 0.05 microgram/ml and 0.10 microgram/ml, respectively. MIC against a strain of Haemophilus influenzae was 3.13 micrograms/ml. MICs of 2 strains of Branhamella catarrhalis were 0.20 microgram/ml. 5. TE-031 is considered to be a new useful and safe antibiotic in pediatric patient with an excellent bactericidal capacity.     

Gelatin microspheres crosslinked with D,L-glyceraldehyde as a potential drug delivery system: preparation, characterisation, in vitro and in vivo studies

To overcome the restriction in using crosslinked gelatin in the pharmaceutical field, D,L-glyceraldehyde (GAL), a non-toxic crosslinking agent, was proposed. Gelatin microspheres crosslinked with different concentrations of GAL (0.5, 1 or 2%, w/v) and for different time periods (1 or 24 h) were prepared. The effect of the preparation variables was evaluated analysing the extent of crosslinking, the morphological aspect, the particle size and the swelling behaviour. To evaluate the pharmaceutical properties, an antihypertensive drug, clonidine hydrochloride, was chosen as drug model and loaded into the microspheres. Either the increase of the crosslinker concentration or of the crosslinking time period decreased both the swelling and the in vitro drug release processes of the microspheres. After the subcutaneous injection, the loaded microspheres crosslinked with the lowest GAL concentration (0.5%, w/v) or for the shortest time period (1 h) showed a reduction of systolic blood pressure (SBP) similar to that recorded with a clonidine hydrochloride solution having the same drug concentration. Instead, the microspheres crosslinked for 24 h with concentrations of GAL higher than 0.5% (w/v) produced a more gradual and sustained SBP reduction and the antihypertensive effect was maintained until 52-72 h. The biocompatibility studies showed that the microspheres crosslinked with GAL are well tolerated in vivo. These results suggest the potential application of gelatin microspheres crosslinked with GAL as a suitable drug delivery system for the subcutaneous administration.     

Crosslinking studies in gelatin capsules treated with formaldehyde and in capsules exposed to elevated temperature and humidity

Incomplete in vitro capsule shell dissolution and subsequent drug release problems have recently received attention. A modified USP dissolution method was used to follow capsule shell dissolution, and a 2,4,6-trinitrobenzenesulfonic acid (TNBS) assay was used to follow loss of epsilon-amino groups to study this shell dissolution problem postulated to be due to gelatin crosslinking. The dissolution problems were simulated using hard gelatin capsule (HGC) shells previously treated with formaldehyde to crosslink the gelatin. These methods were also used to study the effect of uncrosslinked HGC stored under stressed conditions (37 degrees C and 81% RH) with or without the presence of soft gelatin capsule shells (SGC). A 120 ppm formaldehyde treatment reduced gelatin shell dissolution to 8% within 45 min in water at 37 degrees C. A 200 ppm treatment reduced gelatin epsilon-amino groups to 83% of the original uncrosslinked value. The results also support earlier reports of non-amino group crosslinking by formaldehyde in gelatin. Under stressed conditions, HGC stored alone showed little change over 21 weeks. However, by 12 to 14 weeks, the HGC exposed to SGC showed a 23% decrease in shell dissolution and an 8% decrease in the number of epsilon-amino groups. These effects on the stressed HGC are ascribed to a volatile agent from SGC shells, most likely formaldehyde, that crosslinked nearby HGC shells. This report also includes a summary of the literature on agents that reduce gelatin and capsule shell dissolution and the possible mechanisms of this not-so-simple problem.