Paul B. Foreman

Ex vivo bioadhesion and in vivo testosterone bioavailability study of different bioadhesive formulations based on starch-g-poly(acrylic acid) copolymers and starch/poly(acrylic acid) mixtures

Starch-g-poly(acrylic acid) copolymers or grafted starches synthesized by 60Co irradiation or chemical modification and co-freeze-dried starch/poly(acrylic acid) mixtures were evaluated on their ex vivo bioadhesion capacity. The buccal absorption of testosterone from a bioadhesive tablet formulated with the grafted starches or starch/poly(acrylic acid) mixtures was investigated. The results were compared to a reference formulation (physical mixture of 5% Carbopol 974P and 95% Drum Dried Waxy Maize). Rice starch-based irradiated grafted starches showed the best bioadhesion results. Partial neutralization of the acrylic acid with Ca(2+) ions resulted in significantly higher bioadhesion values compared to the reference. Ca(2+) and Mg(2+) partially neutralized maltodextrin-based irradiated grafted starches showed significantly higher bioadhesion values compared to the reference formulation. The chemically modified grafted starches showed significantly higher adhesion force values than for the reference tablet. None of the co-freeze-dried starch/poly(acrylic acid) mixtures showed significantly higher bioadhesion results than the reference (Bonferroni test, P<0.05). A chemically modified grafted starch could sustain the 3 ng/ml plasma testosterone target concentration during +/- 8 h (T(>3 ng/ml)). By lyophilization of a partially neutralized irradiated grafted starch, the in vivo adhesion time (22.0 +/- 7.2 h) and the T(>3 ng/ml) (13.5 +/- 1.3 h) could be increased. The absolute bioavailability of the lyophilized formulation approached the reference formulation. Some of the grafted starches showed to be promising buccal bioadhesive drug carriers for systemic delivery.

Spray-dried powders of starch and crosslinked poly(acrylic acid) as carriers for nasal delivery of inactivated influenza vaccine

Mucosal vaccination has several advantages over parenteral vaccination. In this study, viscosity-enhancing mucosal delivery systems for the induction of an adaptive immune response against viral antigen were investigated. Powder formulations based on spray-dried mixtures of starch (Amioca)/poly(acrylic acid) (Carbopol 974P) in different ratios were used as carriers of the viral antigen. A comparison of these formulations for intranasal delivery of heat-inactivated influenza virus combined with LTR192G adjuvant was made in vivo in a rabbit model. Individual rabbit sera were tested for seroconversion against hemagglutinin (HA), the major surface antigen of influenza. The powder vaccine formulations were able to induce systemic anti-HA IgG responses. The presence of Carbopol 974P improved the kinetics of the immune responses and the level of IgG titers in a dose-dependent way which was correlated with moderately irritating capacities of the formulation. In contrast, mucosal IgA responses were not detected. In conclusion, it was demonstrated that the use of bioadhesive carriers based on Amioca starch and poly(acrylic acid) facilitates the induction of a systemic anti-HA antibody response after intranasal vaccination with a whole virus influenza vaccine.

Trypsin inhibition, calcium and zinc ion binding of starch-g-poly(acrylic acid) copolymers and starch/poly(acrylic acid) mixtures for peroral peptide drug delivery.

Newly synthesised starch-g-poly(acrylic acid) copolymers and starch/poly(acrylic acid) mixtures were evaluated for their in vitro inhibition potency towards the proteolytic enzyme trypsin. Their Ca2+ and Zn2+ binding capacity was measured. Carbopol 934P was used as reference polymer. Starch-g-poly(acrylic acid) copolymers were prepared by chemical grafting and 60Co irradiation, the starch/poly(acrylic acid) mixtures by freeze-drying. The influence of preparation method, the ratio starch:acrylic acid, the neutralisation degree and for the freeze-dried polymers the influence of heat treatment after freeze-drying was investigated. All freeze-dried polymers showed a higher inhibition factor (IF) than the chemically grafted and 60Co irradiated starches, which all showed significantly lower IF than Carbopol 934P. The heat treated freeze-dried polymer Amioca/poly(acrylic acid) (1:1) showed a significantly higher IF than the reference polymer (Mann-Whitney test, p<0.05). The Ca2+ and Zn2+ binding capacity of all chemically grafted starches was much lower than for Carbopol 934P. Only the 60Co irradiated starches and freeze-dried polymers with ratio 1:3 approached the binding capacity of the reference polymer. The freeze-dried polymers showed the highest proteolytic enzyme inhibition potency. Freeze-drying and 60Co irradiation could result in the highest ion binding capacity. This combination of proteolytic enzyme inhibition activity and ion binding capacity makes these polymers hopeful excipients for successful oral peptide delivery.

Evaluation of the mucosal irritation potency of co-spray dried Amioca/poly(acrylic acid) and Amioca/Carbopol 974P mixtures.

The purpose of this study was to evaluate the biocompatibility of different Amioca/poly(acrylic acid) and Amioca/Carbopol 974P co-spray dried mixtures with an alternative mucosal irritation test using slugs. The irritation potential of the mixtures was measured by the amount of mucus produced during a repeated 30-min contact period. Additionally, membrane damage was assessed by measuring the protein and enzyme release from the body wall of slugs after treatment. All the Amioca/poly(acrylic acid) co-spray dried mixtures (50:50 and 25:75 ratios) induced slight irritation of the mucosal tissue as was demonstrated by the significantly increased mucus production however no increased protein and enzyme release was detected. Co-spray dried Amioca/Carbopol 974P mixtures containing 40% and more Carbopol 974P demonstrated a significantly higher mucus production and release of cytosolic LDH, indicating membrane damage. The total mucus production of the slugs treated with the co-spray dried mixtures containing up to 20% Carbopol 974P was significantly higher compared to the blank slugs. However, these mixtures induced no membrane damage since no additional effect on the protein release and no enzyme release was detected. By co-spray drying up to 20% Carbopol 974P could be incorporated without showing a distinct sign of irritation. These mixtures can be considered as potentially safe bioadhesive carriers.

In-vitro and in-vivo evaluation of enteric-coated starch-based pellets prepared via extrusion/spheronisation

Pellet cores containing modified starch (high-amylose, crystalline and resistant starch) as the main excipient were enteric-coated with an Eudragit L30 D-55 based dispersion. The polymer weight gain was from 15% to 30% (w/w). Pellet cores were prepared using piroxicam (2.5% w/w, poor water solubility) and anhydrous theophylline (2.5% and 25% w/w, coarse and micronised powder, medium water solubility) as model drugs. Next to the water solubility, particle size and concentration of the model drugs, the influence of sorbitol (0% and 10%, w/w) and drying method (oven and fluid-bed) on pellet yield, size (Feret mean diameter), sphericity (aspect ratio, AR and two-dimensional shape factor, e(R)), friability, surface morphology and drug release were evaluated. Binder (HPMC) and granulation liquid (water) concentration were optimised to obtain maximum yield (size fraction between 900 and 1400 microm) and acceptable sphericity (AR<1.2). Pellet friability was <0.01% for all formulations, while the mean pellet diameter was lower for pellets with sorbitol and the ones dried in an oven. Mercury intrusion porosimetry combined with scanning electron microscopy revealed an influence of drying method and sorbitol level on the surface structure: the surface of fluid-bed dried pellets without sorbitol and with 2.5% of model drug was cracked, which correlated with a Hg-intrusion peak at the 6-80 microm pore size range. Due to improved mechanical properties of the wet mass, sorbitol addition smoothened the pellets as the main peak of Hg-intrusion shifted to a smaller pore size range. Using a higher drug concentration and micronised theophylline shifted the main peak of Hg-intrusion further towards the smaller pore size range. Oven-dried pellets showed no Hg-intrusion and no cracks were observed. When applying the highest coating thickness (30% weight gain), all theophylline pellet formulations were successfully coated (<10% drug release after 2h in acid dissolution medium), while pellets with the lowest coating thickness (15% weight gain) released from 5% to about 30% theophylline. The extent of drug release depended on the pellet composition and drying method as these factors determined the surface properties. Piroxicam release in acid medium was less than 1% irrespective of the surface characteristics, due to its poor water solubility. In basic medium (phosphate buffer, pH 6.8) all pellets released the drug in less than 45 min. The bioavailability of coated and uncoated piroxicam pellets was determined after oral administration to six dogs. Values of AUC(0-->72h), C(max) and t(max) after oral administration of piroxicam pellets to dogs were not significantly different from the values obtained for immediate release capsules (P>0.05).

Effect on the nasal bioavailability of co-processing drug and bioadhesive carrier via spray-drying.

A mucoadhesive combination of a maize starch (Amioca, mainly consisting of amylopectine) and a cross-linked acrylic acid-based polymer (Carbopol 974P) was spray-dried with metoprolol tartrate (used as model molecule) in order to develop a powder suitable for nasal drug delivery via a one-step manufacturing process. The bioavailability of metoprolol tartrate after nasal administration of this powder to rabbits was compared with powders manufactured via other procedures: (a) freeze-drying of a dispersion prepared using the co-spray-dried powder, (b) freeze-drying of a dispersion prepared using a physical mixture of drug and mucoadhesive polymers. After co-processing via spray-drying a low bioavailability (BA 10.8+/-2.3%) was obtained, whereas manufacturing procedures based on freeze-drying yielded a higher BA: 37.9+/-12.8% using the co-processed powder and 73.6+/-24.9% using the physical mixture. The higher bioavailability was due to the deprotonation of poly(acrylic acid) during neutralisation of the dispersion prior to freeze-drying. This induced repulsion of the ionised carboxyl groups and a lower interaction between poly(acrylic acid) and starch, creating a less compact matrix upon hydration of the polymer and allowing an easier escape of metoprolol tartrate from the matrix. This study showed that co-processing of a mucoadhesive Amioca/Carbopol 974P formulation with metoprolol tartrate via co-spray-drying did not provide any added value towards the bioavailability of the drug after nasal administration of the mucoadhesive powder.

Influence of heat treatment on spray-dried mixtures of Amioca® starch and Carbopol® 974P used as carriers for nasal drug delivery

A mucoadhesive spray-dried starch/poly(acrylic acid) powder underwent different heat treatments in order to induce cross-linking between the functional groups of starch (Amioca) and poly(acrylic acid) (Carbopol 974P). After heat treatment the water-absorbing capacity, viscosity and elasticity of the mucoadhesive powder increased. NMR analysis in combination with FT-IR indicated that heat treatment induced a low degree of cross-linking between the polymers. Nasal administration of Amioca/Carbopol 974P powders without heat treatment resulted in an absolute bioavailability in rabbits of 8.2+/-3.0% for insulin. Due to the difference in water-absorbing capacity (which opened the tight junctions of the nasal mucosa), elasticity and plasticity (which reduced mucociliairy clearance and prolonged residence time) heat treatment at 120 degrees C improved the bioavailability: 26.4+/-21.9, 36.5+/-11.0 and 19.3+/-17.3% after heat treatment during 30 min, 1 h and 4 h, respectively. Heat treatment at 60 degrees C was less efficient. This study demonstrated that the nasal insulin absorption improved via heat treatment of the Amioca/Carbopol 974P powder (prior to the addition of insulin). The bioavailability-enhancing effect of a 1 h heat treatment at 120 degrees C was confirmed using the same polymer matrix in combination with different drugs (salmon calcitonin, human growth hormone and metoprolol tartrate).