Formulation and Evaluation of Multi-Unit Particulate Systems for Delivery of Ampicillin

The oral route of drug administration is the most significant and convenient method of drug delivery. In recent years, Multiple Unit Pellet Systems (MUPS) tablets have gained widespread use in the design of solid dosage forms. MUPS are recognized for offering pharmacokinetic benefits over single-unit dosage forms. These tablets typically contain modified-release pellets, which play a crucial role in pharmaceutical research and development due to their advanced drug delivery capabilities. Pellets are primarily developed for oral modified-release formulations, featuring properties such as gastro-resistance, sustained-release, and the ability to function in Pulsatile Drug Delivery Systems. For these applications, coated pellets are often administered in hard gelatin capsules or fast-disintegrating tablets that rapidly disperse in the stomach. This approach enhances the safety and efficacy of the formulation compared to other dosage forms. Pellets offer a high level of flexibility in the design and development of oral medications. They can be easily divided into desired doses without requiring changes to the formulation or manufacturing process, and they can also be blended to achieve specific drug delivery profiles. Pellets can be manufactured using various methods, depending on their intended application and the preferences of the manufacturer. The most commonly used techniques include extrusion and spheronization, solution or suspension layering, and powder layering. Other methods, such as globulation, balling, and compression, have more limited applications in the production of pharmaceutical pellets. Among these, compressing pellets into tablets is an innovative approach and is often considered more advantageous than encapsulating. .

Advantages of Compacting Multi-Unit Pellet Systems (MUPS) Over Conventional Modified-Release Tablets and Pellet-Filled Capsules

Pharmacokinetic Advantages

1. The small size of micro-pellets in MUPS ensures rapid and uniform transit from the stomach to the small intestine, reducing the risk of localized irritation. This promotes better and more consistent drug absorption.
2. Uniform gastric emptying of micro-pellets into the small intestine allows for quick dissolution of enteric coatings. In controlled-release formulations, drug release is more consistent, minimizing the risk of dose dumping and reducing inter-subject variability.

Pharmacodynamic Advantages

1. The rapid and uniform gastric emptying of pellets, combined with their small size and larger surface area, ensures consistent drug dissolution in the gastrointestinal tract. This results in uniform drug.absorption and a more controlled pharmacological effect.
2. MUPS significantly reduce inter- and intra-subject variability in drug absorption and clinical response. This is because MUPS contain a much higher number of pellets compared to conventional pellet-filled capsules, further minimizing the risk of dose dumping in the stomach and ensuring complete drug release.

Patient-Friendly Dosage Form

MUPS offer improved patient compliance for the following reasons:

1. The mouth-disintegrating MUPS formulation, often designed with a palatable taste, is ideal for pediatric and geriatric patients who struggle with swallowing tablets or capsules.
2. Orodispersible MUPS can be taken without water, making them convenient for use while traveling. These formulations can include flavors and sweeteners that stimulate salivation and ease swallowing.
3. Unlike capsules, MUPS tablets can be designed as divisible dosage forms without affecting the drug release.
4. MUPS have a lower tendency to adhere to the esophagus during swallowing, enhancing patient comfort.
5. The compact size of MUPS tablets improves patient compliance compared to bulkier capsule formulations

Advantages of Multi particulate Tablets

• Enhanced Stability: Pellets embedded in an inert matrix exhibit greater physicochemical and microbiological stability.
• Cost and Processing Efficiency: Lower production costs and higher processing speeds compared to capsules, utilizing existing tableting equipment.
• Reduced Dust Issues: Minimal dust generation during compression, unlike conventional tablets
• Excellent Flow Properties: The spherical shape of pellets ensures superior flow properties, facilitating easier tableting with fewer segregation issues compared to traditional granules.
• Dose Flexibility: Easier dose adjustment by increasing or decreasing the number of pellets in the formulation.
• Customizable Drug Release: Pellets with different release characteristics can be mixed to tailor drug release profiles for MUPS.
• Dose Division Without Compromising Release: Dividing multiparticulate tablets does not affect release properties, as these are determined by individual subunits.

METHODS OF PREPARATION OF PELLETS

Balling

Balling is a pelletization process where finely divided particles are transformed into spherical particles through continuous rolling or tumbling motion, facilitated by the addition of a suitable liquid. The liquid can be introduced either before or during the agitation stage. Equipment such as pans, discs, drums, or mixers can be used to produce pellets via the balling process(Lavanya, Senthil et al. 2011).

Compression

Compression pelletization involves compacting blends of active pharmaceutical ingredients and excipients under pressure to form small, spheroidal pellets suitable for capsule filling. This method utilizes similar formulation and processing parameters as conventional tablet manufacturing, essentially producing miniature tablet-like pellets (Bathool et al., 2011). Globulation techniques encompass two distinct processes: spray drying and spray congealing. Spray drying atomizes drug solutions or suspensions into hot air to generate dry, spherical particles, primarily employed to improve dissolution rates and bioavailability of poorly soluble drugs, though it also finds application in controlled-release pellet development. Spray congealing, on the other hand, involves dispersing or dissolving drugs in molten carriers (e.g., waxes, gums, fatty acids) and spraying them into a cooled chamber to form solidified spherical pellets

Extrusion-spheronization is a multi-stage process that yields uniformly sized spherical particles, offering superior control over particle characteristics compared to conventional granulation but requiring greater time and effort. Developed by Nakahara in 1964, the process consists of four key steps:

Dry Mixing – Ensuring uniform powder dispersion before wet granulation, a critical yet often underestimated step that influences final granule quality.

1. Granulation – Preparing a deformable wet mass, typically using batch mixers, though continuous systems are also viable (Xia et al., 2018).
2. Extrusion – Shaping the wet mass into cylindrical extrudates, a technique also widely used in food, ceramics, and polymer industries, and increasingly in pharmaceutical tablet manufacturing.
3. Spheronization – Converting extrudates into spherical particles via a rotating friction plate, where mechanical interactions refine particle shape and uniformity.

This method is particularly valuable when specific pellet properties are required that cannot be achieved through simpler granulation techniques

Direct Pelletizing

Direct pelletizing involves the production of pellets directly from powder.

• Efficient Process: Pellets are manufactured directly from powder using a binder or solvent, making it a fast process with minimal use of auxiliary materials.
• Product Advantages: Produces compact, round pellets ideal for automatic dosing and uniform coating. Pellet diameters typically range between 0.2 mm and 1.2 mm.
• Comparison: Pellets have a higher density compared to spray granulates and agglomerates(O’Connor and Schwartz 2022).
• Process Principles: The powder is mixed and moistened, with the optional addition of a solvent or binder. The powder bed is set into centrifugal motion (e.g., fluid bed pelletizing in a rotor). The impact and acceleration forces generated during this process lead to the formation of agglomerates, which are then rounded into uniform and dense pellets. The rotation speed directly influences pellet density and size. The moist pellets are subsequently dried in a fluid

Powder Layering

Powder layering is a process where successive layers of dry powder—comprising the drug, excipients, or both—are deposited onto pre-formed nuclei or cores using a binding liquid. Since this method involves the simultaneous application of liquid and dry powder, it typically requires specialized equipment. Tangential spray or centrifugal fluid bed granulators are examples of equipment that have revolutionized powder layering as a pelletization technique. In the case of tangential spray granulators, the rotating disk and fluidization air ensure proper mixing of the materials. In centrifugal granulators with a double wall, the process can be carried out in both open and closed positions. During powder layering, the inner wall is closed to allow the simultaneous application of liquid and powder until the pellets reach the desired size. Once the desired size is achieved, the inner wall is raised, and the pellets move into the drying zone. The fluidization air lifts the pellets up and over the inner wall, returning them to the forming zone. This cycle repeats until the pellets achieve the desired residual moisture level.

MATERIALS AND METHODS:

Chemicals and Reagents

Table 1: List of chemicals

Physicochemical characterization and identification of ampicillin

Physical appearance test:

The physical characteristics of ampicillin were evaluated through organoleptic examination, focusing on key attributes including color, odor, and general appearance. These observed properties were carefully compared against the specifications provided in the manufacturer's certificate of analysis to verify authenticity and quality.

Melting point:

The melting behavior of ampicillin was analyzed using the standard capillary method. Approximately 3 mm of the drug sample was packed into sealed capillary tubes, which were then placed in a melting point apparatus. The temperature was gradually increased while monitoring the sample, with particular attention given to recording both the initial melting temperature and the point of complete liquefaction

Fourier transform infrared spectral analysis:

FTIR characterization of ampicillin was performed using potassium bromide pellet preparation. The drug substance was finely ground and uniformly mixed with KBr powder before being compressed into transparent pellets using hydraulic pressure. The resulting pellets were analyzed by FTIR spectroscopy, and the obtained spectrum was compared against the reference spectrum of itraconazole standard for identification purposes (Liu, Vanderwyk et al. 2024).

UV standard-plot calibration curve:

Methanol was selected as the optimal solvent system for conducting spectrophotometric analysis of ampicillin due to its favorable solubility characteristics.

Determination of absorbance maxima (λ max):

The 100 µg/ml stock solution was serially diluted to prepare solutions ranging from 10-50 µg/ml concentration. These samples were scanned across the UV-visible spectrum (200-800 nm) to identify the wavelength of maximum absorption. Triplicate measurements were conducted for each concentration, with mean absorbance values calculated for accurate determination of λ max.

Preparation of pellets

The process of pellet formation proceeds in4 Steps

1. Feeding the solid material into the extruder and melting or plasticizing it in a thermal carrier, usually a low melting point wax or polymers (starting from high molecularweight polymers to low molecular weight polymers), such as vinyl polymers, co- povidone, polyethylene glycol, acrylates, and cellulose derivatives. Diffusion (ethyl cellulose, carnauba wax) and erosion (HPMC) are the drug release methods (Muley, Nandgude et al. 2016).
2. Extruder conveys mass, flows through the die, and shapes molten substance into uniform cylindrical segments.
3. Extrude spheronization at high temperatures to deform by softening and aid in the formation of uniform spheroids.
4. Solidifying spheroids to achieve the appropriate form, die exit, and downstream processing. The form of extruded items is determined by the endplate die linked to the end of the barrel (Ye, Wang et al. 2007; Swaminathan, Sangwai et al. 2013).                    

Preparation of mass:

For the present study, ampicillin was mixed with citric acid, methyl cellulose (MCC), starch and sodium carboxymethylcellulose were mixed initially to form the mass. Three different batches were prepared to form the mass, as shown in table. The concenetrations of citric acid and MCC were varied to prepare the batches. The total batch size prepared was 5g for each batch (Theismann, K. Keppler et al. 2019).

Table 2- Different batches prepared using varied concentrations of citric acid and MCC.

Extrusion of the mass

Spheronization of the extrudes:

The extrusion process was carefully conducted for each formulation batch (F1-F3) under uniform pressure conditions to obtain consistent extrudes. Preliminary evaluation revealed that batches F1 and F3 produced suboptimal extrudes that exhibited stickiness and irregular morphology, rendering them unsuitable for further processing. In contrast, batch F2 demonstrated excellent extrusion characteristics, forming uniform cylindrical extrudes that met the quality parameters for subsequent spheronization (Sardana, Khurana et al. 2021). The selected F2 extrudes were then processed through spheronization, where controlled heat application and mechanical forces transformed the cylindrical strands into spherical pellets through a combination of plastic deformation and surface tension effects (Chen, Xin et al. 2024).

EVALUATION OF PELLETS

Bulk density

The bulk density of powder is affected by particle packing and changes with powder consolidation. A huge funnel was utilize to pour the bulk powder into a graduated cylinder, and bulk density was produce by measuring the volume and weight. The following formula is use to determine bulk density.

Bulk Density =   weight of powder

Bulk volume

Tapped density

The density produced when a powder is crushed by vibration or tapping is referred to as "tapped density." By setting a graduated cylinder with a specific amount of powder on top of mechanical tapping equipment that is operated for a predetermined number of taps (100) or until the volume of the powder bed reaches a minimum, the taped density was determined. The tapped density was computed using the weight of the drug in the cylinder and its final volume.

Tapped Density = weight of powder

           Tapped Volume

The compressibility index of Carr:

The flow properties of the pellet formulation were quantitatively assessed through Carr's compressibility index, a crucial parameter in predicting material behavior during downstream processing. This index was derived from the relationship between bulk and tapped densities, with values below 15% indicating excellent flow characteristics suitable for capsule filling or tablet compression, while values exceeding 25% signaled potential flow issues requiring formulation adjustments (Mohanthi, Ramya et al. 2022).

Haussner's coefficient:

Hausner's ratio is one indirect way to gauge the ease of powder flow. This is the formula that determines it:

H= Tapped Density

    Bulk Density

Angle of Repose:

The flow characteristics were further evaluated through angle of repose measurements using the fixed funnel method. This test involved forming a powder cone on graph paper and precisely measuring the resulting angle through trigonometric calculations. The angle of repose, influenced by particle size, shape, and surface roughness, provided valuable information about the formulation's handling properties during large-scale production.

θ = tan-1 h/r

Drug content:

Quantitative analysis of drug content was performed for both uncoated cores and finished pellets using validated UV-spectrophotometric methods. The assay procedure involved constructing a calibration curve with reference standards and extracting the drug from pellet matrices to ensure accurate potency determination throughout the manufacturing process.

Particle Size Distribution:

Particle size characterization employed a combination of sieving analysis and Vernier caliper measurements. The methodology involved stacking standardized test sieves in descending mesh sizes and subjecting the sample to mechanical agitation for precise size fractionation. The resulting weight distribution data enabled calculation of mean particle size and size distribution parameters critical for ensuring batch uniformity and predicting in vivo performance

Friability:

Pellet durability was assessed through friability testing using a modified USP apparatus. The test subjected samples to controlled mechanical stress through 200 revolutions, with weight loss measurements providing insight into the formulation's ability to withstand handling and transportation. While conventional tablet standards require <0.8% friability, the evaluation criteria were appropriately adjusted for pellets considering their larger surface area and unique mechanical properties.

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Physicochemical Characterization of ampicillin pellets

Particle size and shape distribution:

Advanced microscopic analysis utilizing LED-illuminated optical systems with digital imaging capabilities provided detailed characterization of pellet morphology. This evaluation included quantitative assessment of size distribution and qualitative analysis of shape parameters, ensuring the spheronization process yielded uniform, spherical particles suitable for subsequent coating or encapsulation processes.

Dissolution studies:

A comprehensive two-stage dissolution protocol was implemented to simulate gastrointestinal conditions. The study commenced with 2 hours in acidic medium (0.1N HCl, pH 1.2) followed by pH adjustment to 5.5 using 0.1N NaOH to mimic intestinal transition. USP Apparatus I (baskets) operated at 75 rpm-maintained sink conditions while temperature was rigorously controlled at 37±0.5°C. Sampling at predetermined intervals followed by spectrophotometric analysis provided complete drug release profiles, with special attention given to potential precipitation phenomena during pH transition.

RESULT AND DISCUSSION

Physicochemical characterization and identification of ampicillin

Physical appearance test:

Ampicillin was classified based on several organoleptic qualities such as color, odor, and appearance. The results were compared to the manufacturer's certificate of authenticity.

Identification and characterization of ampicillin

Physical description: The ampicillin sample was identified and characterized in accordance with the requirements of the manufacturer's COA(certificate of analysis)

Table4:Certificate of analysis of ampicillin parameters

Melting point:

The observed experimental melting point by capillary method complies with the reported melting point as shown in table

Table 5:Certificate of analysis of ampicillin melting range.

UV Standard plot of ampicillin:

The results of UV standard plot are shown in table. Five different concentrations of ampicillin were taken (10,20,30,40 and 50 mcg/ml). The readings for each concentration were taken in triplicate and the mean absorbance was calculated. The absorbance readings were plotted for each concentration and regression line was obtained by setting zero intercept .

Table 6 : Standard plot of ampicillin

Figure : Calibration curve of ampicillinby UVspectroscopy

FTIR Identification and Analysis–

Table 7;Here’s a table summarizing the characteristic IR absorption peaks of ampicillin:

Figure.FTIR of ampicillin

pH-solubilityStudy:

The solubility of ampicillin as a function of pH was evaluated in 10% 0.1 N HCl solution by adding citric acid to aqueous solutions of ampicillin and pH was determined using the apparatus pH meter.

Table8. pH solubility study of ampicillin with different conc of citric acid

Optimization of pellet-Extruderspherionzer

Table15:pictures has been taken on different interv also time during spherionizing process for total of120 seconds.

Time (sec)	Microscope with LED and camera	Remarks
30		Longitudnal cylindrical
60		Size reduced but still longitudnal cylindrical
90		Dumbell shaped
120		Spherical

Characterization of the prepared pellets:

Bulk Density and Tapped Density: The bulk density and tapped density are the necessary parameters for determining the flow properties of the given material. Hence it becomes essential part to estimate the bulk and tapped densities for the prepared pellets. The results are given in the following table.

Table 9: Results of bulk density and tapped density

Carr’s Index: Carr’s index is an indirect measure of the interparticulate forces within the particles and hence their flow ability. Both of them were calculated using the bulk and tap densities of the pellets batchand hence the Carr’s index was calculated.

Haussner’s ratio: the ratio of the tapped and the bulk density gives the Haussner’s Ratio, which is an indirect measure for the ability of the particles to make a good flow. Ideally, the 1-1.11 ratio, signifies excellent flowability. The results observed are shown in the table. As the pellets had the good potential to flow.

Angle of Repose:

The flow characteristics of the developed pellets were evaluated using the angle of repose test, which demonstrated excellent micromeritic properties. The mean angle of repose (n=3) was found to be 20°, which falls well below the threshold of 25°, indicating superior powder flow behavior. This result aligns with the classification of excellent flowability, as angles of repose below 25° are typically associated with free-flowing powders. The findings are consistent with previous research by Sinha et al. (2005), who also reported that an angle of repose less than 25° signifies good flow potential for pellets. This suggests that the developed pellets possess optimal flow properties, which are crucial for uniform filling, dosing, and further processing in pharmaceutical applications.

Particle Size Distribution:

The particle size of pellets plays a critical role in determining dissolution rate and drug content uniformity, as highlighted by Priese and Wolf (2013). A consistent particle size distribution is essential to ensure predictable dissolution behavior and homogeneous drug distribution. The experimental results revealed that the pellet size was 1597 ± 204 µm, as supported by recent findings from Kállai-Szabó et al. (2024). This narrow size distribution indicates good uniformity, which is favorable for achieving reproducible drug release profiles and minimizing batch-to-batch variability. The relatively larger pellet size may also contribute to improved mechanical strength, reducing the risk of breakage during handling and processing.

Friability:

The friability test was conducted to assess the mechanical durability of the pellets, with the percentage weight loss serving as an indicator of their resistance to abrasion and breakage.

DissolutionStudy:

The binary combination of ampicillin with citric acid (20% drug load) was combined with a super disintegrant (10% w/w) and compressed into pellets. 100 mg ampicillin (total capsule weight=500 g). The capsules started dissolving in 250 mL of 0.1 N HCL. (pH 1.5) for 125 minutes at 75 RPM and 37°C, and then the vol. of dissolution media was made up to 500mLwith pH adjustment to 5.5 using 0.1N NaOH.

Figure: Percentage drug release from dissolution studies