Effect of different sterilisation methods on the properties of bioadhesive powders and ocular minitablets, and clinical evaluation

The revival of the mini-tablets: Recent advancements, classifications and expectations for the future

Mini-tablets have recently raised huge interest in pharmaceutical industry. The present review aims to identify the rational, the opportunities and challenges of this emerging small solid drug dosage form by a structured literature review following the PRISMA algorithm. In total, more than 5,000 literature and patent sources have been found starting with the very first in the 60s of the past century, followed by the first multiparticular products using mini-tablets with pancreatin (Panzytrat® by the former BASF subsidiary Knoll/Nordmark) authorized in 1985. There seems to be a second boost of common interest in the 2000s when clinical studies demonstrated that one or more mini-tablets could enable superior drug administration even in very young patients including neonates over the former gold standard, a liquid drug preparation. Several pharmaceutical companies immediately started clinical development programs using the mini-tablet concept and the first products have been recently authorized by the competent authorities. Superiority was given as the mini-tablets ease the swallowing procedure compared to conventional tablets, enable various modified drug release opportunities including taste-masking by film-coating technology and provide excellent drug stability compared to liquid oral dosage forms. Due to these product attributes they are particularly beneficial to children and their caregivers. Furthermore, there is potential for precise individual drug dosing by counting adequate amounts of the multiple drug carriers. Most recently, two novel products with different concepts were authorized by the EMA and entered the market which are highlighted in this review: the first orodispersible mini-tablet with enalapril maleate for congenital heart failure (Aqumeldi® from Proveca Pharma) and the first single unit mini-tablet with matrix-type controlled melatonin release for insomnia (Slenyto® from Neurim Pharmaceuticals). Our review reveals, that the majority of the published scientific papers use co-processed, ready-to-use excipients for the orodispersible mini-tablet formulations. However, traditional fillers such as microcrystalline cellulose or lactose have also been used for immediate release mini-tablets after adding a (super)disintegrant and a lubricant. The manufacturing of mini-tablets is conducted on conventional rotary tablet presses, predominantly equipped with multi-tip toolings to improve the yield or production speed. Scaling-up has been successfully realized from compaction simulators to pilot and production scale. Film-coatings enabling gastric resistance, taste masking or sustained-release properties have been realized in both fluid-bed and drum coaters using the same polymers as for conventional tablets. There is still a significant lack in regulatory guidance despite the recent success of the mini-tablet concept, starting from suitable characterization methods in the pharmacopoeias up to the design and conduct of clinical studies on mini-tablets.

Poly(amino acid) based fibrous membranes with tuneable in vivo biodegradation

In this work two types of biodegradable polysuccinimide-based, electrospun fibrous membranes are presented. One contains disulfide bonds exhibiting a shorter (3 days) in vivo biodegradation time, while the other one has alkyl crosslinks and a longer biodegradation time (more than 7 days). According to the mechanical measurements, the tensile strength of the membranes is comparable to those of soft the connective tissues and visceral tissues. Furthermore, the suture retention test suggests, that the membranes would withstand surgical handling and in vivo fixation. The in vivo biocompatibility study demonstrates how membranes undergo in vivo hydrolysis and by the 3rd day they become poly(aspartic acid) fibrous membranes, which can be then enzymatically degraded. After one week, the disulfide crosslinked membranes almost completely degrade, while the alkyl-chain crosslinked ones mildly lose their integrity as the surrounding tissue invades them. Histopathology revealed mild acute inflammation, which diminished to a minimal level after seven days.

Radiation sterilization of new drug delivery systems

Radiation sterilization has now become a commonly used method for sterilization of several active ingredients in drugs or drug delivery systems containing these substances. In this context, many applications have been performed on the human products that are required to be sterile, as well as on pharmaceutical products prepared to be developed. The new drug delivery systems designed to deliver the medication to the target tissue or organ, such as microspheres, nanospheres, microemulsion, and liposomal systems, have been sterilized by gamma (γ) and beta (β) rays, and more recently, by e-beam sterilization. In this review, the sterilization of new drug delivery systems was discussed other than conventional drug delivery systems by γ irradiation.

In vitro evaluation of gentamicin- and vancomycin-containing minitablets as a replacement for fortified eye drops

OBJECTIVE

Ocular bioadhesive minitablets containing gentamicin and vancomycin were developed using different powder mixtures of pregelatinized starch and Carbopol (physical or cospray-dried mixtures).

METHODS

Drug content, antimicrobial activity, and radical formation of the powders used for tablet preparation were evaluated immediately and 30 days after gamma sterilization. Tablet properties and in vitro drug release from the sterilized minitablets were determined. Storage stability of vancomycin and gentamicin in sterilized bioadhesive mixtures was examined by LC-UV/MS and a microbiological assay, respectively. A bioadhesive powder mixture containing only vancomycin was irradiated by X electron-magnetic radiation to evaluate vancomycin stability following sterilization through irradiation.

RESULTS

The antimicrobial activity of gentamicin against Staphylococcus epidermidis was not altered in comparison to nonsterilized formulations. Only after an overkill dose of 50 kGy, the concentration of vancomycin decreases to an extent that was pharmaceutically significant. No significant difference in radiation stability between drug substance and product (i.e., powder mixture) was observed. A shift in stability profile was not observed at 6 weeks after irradiation. All other degradation products were present only in small quantities not exceeding 1.0%. The in vitro drug release from the minitablets prepared with physical powder mixtures of pregelatinized starch and Carbopol® 974P NF (96 : 4) was faster compared to the cospray-dried mixtures of starch with Carbopol® 974P NF (ratio: 95:5 and 85:15). The electron paramagnetic resonance signals of the radicals formed during sterilization were still visible after storage for 30 days. The slug mucosal irritation test indicated mild irritation properties of the bioadhesive powder mixtures although no tissue damage was observed.

Evaluation of the in vivo behaviour of gentamicin sulphate ocular mini-tablets in ponies

The in vivo behaviour of 5% gentamicin sulphate ocular mini-tablets (2-mm diameter, 6.525 mg weight) was compared with gentamicin eye drops in six ponies. Two mini-tablets were inserted on the bulbar conjunctiva of the right eye while a similar dose of gentamicin was administered via eye drops in the left eye. Irritation induced by the mini-tablets and the eye drops was evaluated using a visual analogue scale (0-10). Tears were sampled with ophthalmologic absorption triangles for 1 min for the determination of the concentration of gentamicin sulphate using a microbiological plate diffusion method. Irritation induced by the tablets was minor and clinically acceptable (overall median score of 1.7 +/- 1.4). Eye drops induced a sharp increase in gentamicin sulphate concentration (364.4 microg/mL after 5 min) followed by a fast decline (10.8 microg/mL after 60 min). The increase in concentration induced by the ocular mini-tablets was less pronounced (up to 56.2 microg/mL after 30 min) and followed by a gradual decrease; the concentration remained above 15 microg/mL for 8 h. Ocular 5% gentamicin sulphate mini-tablets are clinically well-tolerated in ponies, assuring a constant concentration in the tears for at least 8 h.

Characterization and in vivo evaluation of ocular minitablets prepared with different bioadhesive Carbopol–starch components

The purpose of this study was to evaluate different bioadhesive ocular formulations based on drum dried waxy maize starch (DDWM), Amioca starch and Carbopol 974P. The concentrations of Carbopol 974P in the mixtures varied between 5 and 25% (w/w). The rheological properties of the non-sterilized and gamma-irradiated physical blends of Carbopol 974P with either DDWM or Amioca were compared to those of the corresponding co-spray dried Amioca starch/Carbopol powders. Higher viscosity or consistency values were measured for sterilized co-spray dried powder mixtures containing an amount of Carbopol 974P equal or above 15% (w/w) compared to the physical blends. Sustained release minitablets (2 mm, 6 mg), consisting of sodium fluorescein as model drug and the bioadhesive powders, were manufactured at a compression force of 1.25 kN. Afterwards, the tablets were sterilized with gamma-irradiation. The amount of Carbopol in the co-spray dried powder mixtures on the one hand and gamma-irradiation on the other hand had no significant influence on the crushing strength and friability of the minitablets evaluated. However, these two factors affected the in vitro release properties of the minitablets. The slowest release was obtained with tablets containing 25% Carbopol 974P, which unfortunately possess mucosal irritating properties. By using co-spray dried Amioca with 15% (w/w) Carbopol 974P, a slower release can be achieved compared to the physical mixtures of DDWM or Amioca starch with Carbopol 974P. Moreover, this ocular formulation is very promising and is preferred, as it did not cause any mucosal irritation and released the model drug for at least 12 h, after application in the fornix.

The effect of freeze-drying with different cryoprotectants and gamma-irradiation sterilization on the characteristics of ciprofloxacin HCl-loaded poly(D,L-lactide-glycolide) nanoparticles

In the present study, the influence of freeze-drying with several cryoprotective agents and gamma (gamma)-irradiation sterilization on the physicochemical characteristics of ciprofloxacin HCl-loaded poly(D,L-lactide-co-glycolide) (PLGA) nanoparticles was evaluated. Nanoparticles were prepared by W/O/W emulsification solvent evaporation followed by high-pressure homogenization. They were freeze-dried in the presence of 5.0% (w/v) mannitol, trehalose or glucose, with 5.0% (w/v) or 15.0% (w/v) dextran as cryoprotectants. The nanoparticles were irradiated at a dose of 25 kGy using a 60Co source. The following physicochemical properties of the formulations were investigated: the ratio of particle size before (initial) and after freeze-drying, the ease of reconstitution of the nanoparticle suspensions and the drug-release profiles of irradiated and non-irradiated nanoparticles. The antibacterial activity against Pseudomonas aeruginosa was measured. The freeze-drying process induced a significant increase in particle size when no cryoprotectant was employed. Similar results were observed when cryoprotectants were added to the formulation. Only when mannitol was used was no significant size increase measured. Moreover, for formulations with dextran, reconstitution after freeze-drying was difficult by manual agitation and particle size could not be determined because of aggregation. After gamma-sterilization no significant difference in mean particle size was observed, but reconstitution was more difficult and drug release was influenced negatively. Ciprofloxacin HCl incorporated in the nanoparticles was still effective against the micro-organism selected after freeze-drying and gamma-sterilization.

Effects of roller compaction settings on the preparation of bioadhesive granules and ocular minitablets

An experimental factorial design was employed to evaluate bioadhesive granules and bioerodible ocular minitablets (6 mg and Psi 2 mm). The purpose of this study was to compare minitablets prepared using roller compacted granules with an optimised minitablet formulation, manufactured on laboratory scale by direct compression. The formulation consisted of drum dried waxy maize starch, Carbopol 974P, and ciprofloxacin in a ratio of 90.5/5/3 (w/w/w). Three roller compactor parameters were varied, i.e. the roller speed, the horizontal screw speed and the compaction force, while the vertical screw speed was kept constant. Afterwards, the ribbons were milled to obtain granules suitable for compression. The friability, the flow properties, the bulk material characteristics (apparent and tap density and porosity) and the particle size distributions of two granule sieve fractions (90-125 and 125-355 microm) were investigated. The roller speed and the compaction force have the largest influence on the granule characteristics, followed by the horizontal screw speed. The physical properties of non- and gamma-irradiated minitablets were determined. From the tablet strength, friability and dissolution results, a low compaction force and a high roller speed were shown to be preferable to prepare granules which can be further tabletted into adequate ocular minitablets.