An investigation of the pore structure of tablets of sucrose and lactose by mercury porosimetry

Characterisation of pore structures of pharmaceutical tablets: A review

Traditionally, the development of a new solid dosage form is formulation-driven and less focus is put on the design of a specific microstructure for the drug delivery system. However, the compaction process particularly impacts the microstructure, or more precisely, the pore architecture in a pharmaceutical tablet. Besides the formulation, the pore structure is a major contributor to the overall performance of oral solid dosage forms as it directly affects the liquid uptake rate, which is the very first step of the dissolution process. In future, additive manufacturing is a potential game changer to design the inner structures and realise a tailor-made pore structure. In pharmaceutical development the pore structure is most commonly only described by the total porosity of the tablet matrix. Yet it is of great importance to consider other parameters to fully resolve the interplay between microstructure and dosage form performance. Specifically, tortuosity, connectivity, as well as pore shape, size and orientation all impact the flow paths and play an important role in describing the fluid flow in a pharmaceutical tablet. This review presents the key properties of the pore structures in solid dosage forms and it discusses how to measure these properties. In particular, the principles, advantages and limitations of helium pycnometry, mercury porosimetry, terahertz time-domain spectroscopy, nuclear magnetic resonance and X-ray computed microtomography are discussed.

Comparative Study Between Different Ready-Made Orally Disintegrating Platforms for the Formulation of Sumatriptan Succinate Sublingual Tablets

Sumatriptan succinate (SS) is a selective serotonin receptor agonist used for the treatment of migraine attacks, suffering from extensive first-pass metabolism and low oral bioavailability (∼14%). The aim of this work is to compare the performance of different ready-made co-processed platforms (Pharmaburst®, Prosolv ODT®, Starlac®, Pearlitol Flash®, or Ludiflash®) in the formulation of SS sublingual orodispersible tablets (ODTs) using direct compression technique. The prepared SS ODT formulae were evaluated regarding hardness, friability, simulated wetting time, and in vitro disintegration and dissolution tests. Different mucoadhesive polymers-HPMC K4M, Carbopol®, chitosan, or Polyox®-were tested aiming to increase the residence time in the sublingual area. A pharmacokinetic study on healthy human volunteers was performed, using LC/MS/MS assay, to compare the optimum sublingual formula (Ph25/HPMC) with the conventional oral tablet Imitrex®. Results showed that tablets prepared using Pharmaburst® had significantly (p < 0.05) the lowest simulated wetting and in vitro disintegration times of 17.17 and 23.50 s, respectively, with Q _5 min of 83.62%. HPMC showed a significant (p < 0.05) increase in the residence time from 48.44 to 183.76 s. The relative bioavailability was found to be equal to 132.34% relative to the oral tablet Imitrex®. In conclusion, Pharmaburst® was chosen as the optimum ready-made co-processed platform that can be successfully used in the preparation of SS sublingual tablets for the rapid relief of migraine attacks.

Comparative study of different approaches for preparation of chlorzoxazone orodispersible tablets

CONTEXT

Muscle spasm is a painful involuntary contraction of muscles, which causes involuntary movement and distortion. Chlorzoxazone is a centrally acting muscle-relaxant with sedative properties, but given orally, it is hepatically metabolized leading to decreased bioavailability.

OBJECTIVE

Orodispersible tablets (ODTs) of chlorzoxazone were formulated using two different approaches; by coprocessed excipients (CE) or by liquisolid (LS) technique.

MATERIALS AND METHODS

Pharmaburst^® 500, Starlac^®, Pearlitol flash^®, Prosolv^® odt and F-melt^® were used as coprocessed superdisintegrants, whereas in LS, Avicel^® PH101, Microcelac^® 100 and Cellactose^® 80 were used as carriers, while Aerosil^® 200 was the coating material. ODTs were evaluated in terms of weight and thickness variations, drug content, hardness, friability, wetting time, dissolution, disintegration time (DT) and palatability.

RESULTS

In vitro DT of CE-ODTs ranged from 26.43 ± 1.693 s to >180 s, whereas it was between 25.42± 0.203 s to >180 s in LS-ODTs. Complete drug release within 15 min was attained by CE1 prepared with 92.5 mg Pharmaburst^® 500. In vivo DT of CE1 and LS3 were 19.779 ± 0.810 and 18.105 ± 0.423 s, respectively, using six volunteers. Volunteers found that CE1 had more acceptable taste and was more palatable than LS3.

CONCLUSION

It was concluded that chlorzoxazone ODTs could be successfully formulated using either CE or LS techniques and be used as novel dosage forms for pediatrics and geriatrics showing improved drug release. Moreover, CE technique was superior to LS technique in terms of palatability.

A pharmaceutical study on chlorzoxazone orodispersible tablets: formulation, in-vitro and in-vivo evaluation

CONTEXT

Muscle spasm needs prompt relief of symptoms. Chlorzoxazone is a centrally muscle relaxant.

OBJECTIVES

The aim of this study was to prepare chlorzoxazone orodispersible tablets (ODTs) allowing the drug to directly enter the systemic circulation and bypassing the first-pass metabolism for both enhancing its bioavailability and exerting a rapid relief of muscular spasm.

MATERIALS AND METHODS

ODTs were prepared by direct compression method using Pharmaburst®500, Starlac®, Pearlitol flash®, Prosolv® odt and F-melt® as co-processed excipients. Three ratios of the drug to the other excipients were used (0.5:1, 1:1 and 2:1).

RESULTS AND DISCUSSION

All ODTs were within the pharmacopeial limits for weight and content. ODTs containing Pharmaburst®500 showed the shortest wetting time (∼45.33 s), disintegration time (DT) (∼43.33 s) and dissolution (Q_15min 100.63%). By increasing the ratio of CLZ: Pharmaburst®500 from 0.5:1 to 1:1 and 2:1, the DT increased from 26.43 to 28.0 and 43.33 s, respectively. By using Prosolv® odt, ODTs failed to disintegrate in an acceptable time >180 s. DT of ODTs using different co-processed excipients can be arranged as follows: Pharmaburst® 500 < F-melt® <Pearlitol flash® <Starlac® <Prosolv® odt. Pharmacokinetic study of the optimum formula F1 (50 mg CLZ) in rabbits using HPLC-UV detector revealed a shorter T_max (0.333 h) compared with Myofen® capsules (250 mg CLZ) (1.083 h) which is considered a promising treatment, especially for the rapid relief of muscle spasm.

CONCLUSION

It could be concluded that orodispersible tablets are a promising carrier for CLZ designed for management of muscle spasm due to the enhanced dissolution and rapid absorption of the drug through the oral mucosa.

Microwave Drying of Granules Containing a Moisture-Sensitive Drug: A Promising Alternative to Fluid Bed and Hot Air Oven Drying

The impact of microwave drying and binders (copolyvidone and povidone) on the degradation of acetylsalicylic acid (ASA) and physical properties of granules were compared with conventional drying methods. Moist granules containing ASA were prepared using a high shear granulator and dried with hot air oven, fluid bed or microwave (static or dynamic bed) dryers. Percent ASA degradation, size and size distribution, friability and flow properties of the granules were determined. Granules dried with the dynamic bed microwave dryer showed the least amount of ASA degradation, followed by fluid bed dryer, static bed microwave oven and hot air oven. The use of microwave drying with a static granular bed adversely affected ASA degradation and drying capability. Dynamic bed microwave dryer had the highest drying capability followed by fluid bed, static bed microwave dryer and conventional hot air oven. The intensity of microwave did not affect ASA degradation, size distribution, friability and flow properties of the granules. Mixing/agitating of granules during drying affected the granular physical properties studied. Copolyvidone resulted in lower amount of granular residual moisture content and ASA degradation on storage than povidone, especially for static bed microwave drying. In conclusion, microwave drying technology has been shown to be a promising alternative for drying granules containing a moisture-sensitive drug.

Correlation and prediction of moisture-mediated dissolution stability for benazepril hydrochloride tablets

PURPOSE

This report investigated dissolution stability of benazepril hydrochloride tablets.

METHODS

Reduction in dissolution rate was observed for benazepril hydrochloride tablets when they were subjected to stressed storage condition (40 degrees C/75% RH) for prolonged periods of time (1-3 months). Moisture contents of initial and stressed tablets were measured by Karl Fischer method. Comparative thermal and physical characterizations of initial and stressed tablets were also performed. A mathematical model that was used to predict possible reduction in dissolution rate was proposed and validated using experimental data.

RESULTS

It was found that there was a direct correlation between moisture content of benazepril hydrochloride tablets and their percentage of dissolution at 10 min. At moisture content below 3.5%, there were no significant changes in dissolution values. Beyond that point, however, a close to linear decrease in dissolution was observed as a function of increase in moisture content. Results from thermal and X-ray analysis have ruled out possible changes in drug substance. Other physical characterization, such as scanning electron microscope and mercury porosimetry measurements, revealed changes in core structure of stressed tablets vs. initial tablets. Based on results from these measurements, "preactivation" of disintegrant was identified as the mechanism for reduction in dissolution rate above critical moisture content. A simple physical model for moisture uptake of benazepril hydrochloride tablets was also proposed for predicting when, based on water vapor transmission and critical moisture content, dissolution rate will decline.

CONCLUSIONS

Physical changes of tablets mediated by moisture were the main cause for reduction in dissolution. Inclusion of desiccant, although beneficial, cannot prevent reduction in dissolution completely. The simple physical model proposed in this report was found to be useful in predicting the dissolution stability of the dosage form.

How do roll compaction/dry granulation affect the tableting behaviour of inorganic materials?

The effect of roll compaction/dry granulation on the ribbon and tablet properties produced using different magnesium carbonates was evaluated. The ribbon microhardness and the pore size distribution of tablets were used as evaluation factors. Increasing the specific compaction force resulted in higher microhardness for ribbons prepared with all four magnesium carbonates accompanied with decreased part of fine. Consequently, the corresponding produced tablets displayed a lower tensile strength. A possible correlation between the particle shape, surface area and the resulting pore structure of tablets produced with the four different types of magnesium carbonate was observed. The tensile strength of tablets prepared using granules was lower than tensile strength of tablets produced using starting materials. The partial loss of compactibility resulted in a demand of low loads during roll compaction. However, the impact of changes in the material properties during the roll compaction depended greatly on the type of magnesium carbonate, the specific compaction force and the tableting pressure applied.

Multi-unit controlled release systems of nifedipine and nifedipine:pluronic F-68 solid dispersions: characterization of release mechanisms

Nifedipine (N) and nifedipine. Pluronic F-68 solid dispersion (SD) pellets were developed and characterizedfor drug release mechanisms from a multi-unit erosion matrix system for controlled release. Nifedipine was micronized using a jet mill. Solid dispersion with Pluronic F-68 was prepared by the fusion method. Nifedipine and SD were characterized by particle size analysis, solubility, differential scanning calorimetry (DSC), and x-ray diffraction (XRD) studies. Samples were subsequently processed into matrix pellets by extrusion/spheronization using Eudragit L 100-55 and Eudragit S 100 as release rate-controlling polymers. Drug release mechanisms from pellets were characterized by microscopy and mercury intrusion porosimetry; DSC and XRD studies indicated no polymorphic changes in N after micronization and also confirmed the formation of SD of N with Pluronic F-68. Pellets of N showed a 24-hr drug release profile following zero-order kinetics. Pellets of SD showed a 12-hr release profile followingfirst-order kinetics. Aqueous solubility of N after SD formation was found to be increased 10-fold. Due to increased solubility of N in SD, the drug release mechanism from the multi-unit erosion matrix changed from pure surface erosion to an erosion/diffusion mechanism, thereby altering the release rate and kinetics.

Granule deformation and densification during compression of binary mixtures of granules

The purpose of this study was to investigate whether the deformation and densification during compression of one type of granules are affected by adjacent granules of a different porosity, corresponding to different mechanical strength. Three mixtures were prepared, each consisting of two types of microcrystalline cellulose pellets (intermediate porosity study pellets plus low, intermediate or high porosity surrounding pellets) in the proportion 1:7. The mixtures were compressed and the study pellets were retrieved and analysed in terms of porosity, thickness, surface area and shape. It was shown that the study pellets were compressed by deformation and densification. The degree of densification (decrease in porosity) of the study pellets was independent of the porosity of the surrounding pellets but the deformability (changes in the thickness, surface area and shape) of the study pellets was linked with the porosity of the surrounding pellets. It is concluded that the mode of deformation of the study pellets was regulated by the porosity of the surrounding granules; in a mixture containing granules with a low porosity, compression resulted in irregular study granules with regularly positioned indentations caused by the surrounding granules. The compression properties of the surrounding granules affected the flattening of the study granules to a lesser degree.

Effect of formulation and process variables on porosity parameters and release rates from a multi unit erosion matrix of a poorly soluble drug

The effect of drug loading, water required for granulation and spheronization time on porosity parameters (intrusion-extrusion isotherms, pore size distribution, total pore surface area, mean pore diameter, shape and morphology of pores) and drug release rates from pellets of a poorly soluble drug was investigated. Porosity parameters were determined by mercury intrusion porosimetry. The drug loading was found to have a profound effect on the porosity parameters. Pellets with low drug loading showed increased pore surface area with small mean pore diameters and an increased number of total pores. On the other hand, pellets with high drug loading had decreased pore surface areas with larger mean pore diameters and a reduction in the total number of pores. With high drug loading, the drug release rate decreased. Water required for granulation had a direct effect on the total porosity of the pellets. Spheronization time from 2 to 10 min had a pronounced effect on porosity parameters and release rates. No changes in porosity parameters and release rates were observed from 10 to 20 min of spheronization time. It was shown that each porosity parameter investigated was well correlated with drug release rates and thus it is important to study the effect of porosity parameters in evaluating the in vitro performance of the multi-unit erosion matrix for the controlled release of a poorly soluble drug.

Influence of chopper and mixer speeds and microwave power level during the high-shear granulation process on the final granule characteristics

Although microwave drying technology has been used extensively, detailed studies in the pharmaceutical field are necessary to model the different operational parameters involved in microwave drying in combination with the high-shear granulation processes. The implications of the chopper and the mixer speeds during the granulation step and the microwave power level during the drying step on the final granule characteristics were investigated. alpha-Lactose monohydrate and microcrystalline cellulose were granulated at three different mixer and chopper speeds in a laboratory-scale high-shear mixer (Mi-Mi-Pro) and dried at three microwave power levels. The dried granules were characterized by friability tests, particle size analysis, bulk and tapped density studies, and porosimetry. Neither the mixer speed nor the chopper speed had a significant influence on the granule friability, which was low for all batches produced. The selected materials and experimental conditions induced a very robust granulation process, but the granule size distribution was influenced by the microwave power level. The reciprocal relationship between the dust formation and the microwave power level was analyzed using a central composite factorial design. The amount of dust remained low in all batches, but it influenced some of the inherent density properties and the volume reduction behavior of the granulation mass. In almost all cases, the Carr index decreased slightly with increasing microwave power. The major granule characteristics were not changed when different mixer or chopper speeds were changed, although the mixer speed did alter the intragranular pore size distribution.

Dependence between dissolution rate and porosity of compressed erythromycin acistrate tablets

The correlation between dissolution rate and porosity of compressed erythromycin acistrate tablets was studied. The total porosity of the tablets, the pore size distribution and the specific surface area of the pores were determined using high-pressure mercury porosimetry. The particle size and specific surface area of the raw material and of the dry granulated mass of the tablets were also determined. The results show that the pore size distribution, showing the differences in pore structure, is more informative than total intruded volume of mercury. However, it is very difficult to explain the dissolution behaviour of erythromycin acistrate tablets only by porosity results of the tablets, and more work is still needed in this field.

Determination of porosity and pore-size distribution of aspirin tablets relevant to drug stability

Total porosity and pore-size distribution of aspirin tablets prepared from aspirin, starch USP, and precipitated colloidal silicon dioxide were determined using mercury porosimetry. The model represented a hydrolyzable drug substance in combination with simple excipients. The role of starch and silicon dioxide on the microstructure of the tablets was investigated, as was the chemical stability of various systems. In general, the porosity of tablets containing a constant quantity of starch increased linearly with silicon dioxide concentration. Examination of the pore-size distribution, however, revealed that a low concentrations silicon dioxide functioned primarily to reduce the size and volume of coarse pores representing the spaces between the agglomerates of starch and aspirin particles. This effect was optimum at 3%. A further increase in silicon dioxide concentration produced tablets with relatively larger pore sizes. Studies of changes in the porosity characteristics of tablets as influenced by water vapor over time showed distinct differences in this complex parameter. A unique trend in the change of the pore-size distribution was noted with tablets containing 3% silicon dioxide. These observations are discussed relative to the stability of aspirin tablets in which this concentration of silicon dioxide produced a maximum stabilizing effect.