Preparation and Characterization of Controlled-Release Floating Bilayer Tablets of Esomeprazole and Clarithromycin

Controlled-release effervescent floating bilayer tablets reduce dosage frequency and improve patient compliance with enhanced therapeutic outcomes. Generally, two different tablets of clarithromycin and esomeprazole, respectively, are given for the treatment of Helicobacter pylori infection and it might be worth incorporating both in a single tablet. In the current study, controlled-release floating bilayer tablets of clarithromycin and esomeprazole (F1–F4) were developed with different rates of polymeric materials by a direct compression method. During the formulation, Fourier-transform infrared spectroscopy (FTIR) analysis was performed for possible interactions between drugs and excipients. No interactions between drugs and excipients were noted. Moreover, the bilayer tablets’ thickness, diameter, friability, hardness, weight variation, dissolution, and percent purity were found within the acceptable limits. The floating lag time and total floating time of all formulations were found to be < 25 s and 24 h, respectively. The release of both the clarithromycin and esomeprazole started at the same time from the controlled-release floating bilayer tablets by anomalous non-Fickian diffusion, and the polymeric materials extended the drug release rate up to 24 h. In the case of F1, the results approached ideal zero-order kinetics. The dissolution profiles of the tested and reference tablet formulations were compared, but no significant differences were observed. It can be concluded that such controlled-release effervescent floating bilayer tablets can be efficiently used in clinical practice to reduce dosage frequency and increase patient compliance with continuous drug release for 24 h, which ultimately might enhance therapeutic efficacy.


Introduction
Floating drug delivery systems are designed to deliver drugs with low intestinal solubility or poor stability into the stomach by floating over the gastric fluid due to their low-density [1,2]. These dosage forms are embedded within tablets made of hydroxypropyl cellulose and sodium and citric bicarbonate, two gas-generating agents that, when coming into contact with gastric fluid, generate carbon dioxide, which promotes the floating of the tablets [3].
The reported optimum ratio of citric and sodium bicarbonate for carbon dioxide generation is 0.76:1. The aforementioned tablets may be single-layered or bi-layered; in this latter case, the gas-generating agents are in one layer and the drug is added in the sustained-release portion layer [1]. Moreover, they are made of either natural polymers (Xanthan gum, Gellan gum chitosan, Guar gum, sodium alginate) or synthetic polymers (Eudragit, Ethylcellulose, hydroxypropyl cellulose) [4].
Drugs with a shorter half-life (2-6 h), better bioavailability, dissociation constant >2.5, partition constant >1, and stability in an acidic environment are suitable for the inclusion in floating drug delivery systems [5]. These systems allow a controlled drug release for an extended period, keeping the dose at the absorption site and therefore improving the bioavailability [6].
Helicobacter pylori management with proton pump inhibitors, e.g., esomeprazole, clarithromycin 500 mg, amoxicillin 1 g, or metronidazole 400 or 500 mg, is known to lower the risk of gastroduodenal ulcers and avoid its relapse. Despite that, a 14-day regimen may be more beneficial than a 7-day one, the optimum effective period of therapy is still a matter of debate [7,8].
Esomeprazole is a proton pump inhibitor for the management of gastroesophageal reflux disease (GERD) and the recovery and maintenance treatment of erosive esophagitis, but it is also a component of the triple-drug regimen for the Helicobacter pylori infection [9].
On the other hand, clarithromycin is a broad-spectrum antibiotic belonging to the macrolides class with a molecular weight of 747.95 Dalton, a pKa value of 8.99, a half-life of 4 h, soluble acetonitrile, ethanol, and acetone, slightly soluble in methanol, and poorly soluble in water (0.33 mg/L) [10]. Clarithromycin-based floating matrix tablets have been developed using hydroxypropyl cellulose K15M, hydroxypropyl cellulose K4M, hydroxypropyl cellulose, and hydroxyethylcellulose, obtaining an in vitro controlled release of the antibiotic [11]. Moreover, floating matrix tablets have also been developed using a natural polymer, e.g., pomegranate peels powder, achieving a floating time of 5 h and a 98.67% of drug release [12].
In the current research, new controlled-release floating bilayer tablets of esomeprazole and clarithromycin were prepared and assessed for various physicochemical characteristics, such as a dimensional test, friability, hardness, and weight variation, and in vitro evaluation.

Tablets Formulation
A total of 144 clarithromycin and esomeprazole controlled-release floating bilayer tablets were formulated to allow a constant amount of drug release, while polymeric materials differed depending on the formulation, as shown in Table 1. In each formulation, a gas-generating agent was also added to bring the tablet to the surface in a simulated gastric medium (0.1 N HCl).

Flow Properties
Flow parameters such as Hausner ratio, compressibility index, and angle of repose were determined according to standard procedures for powder mixtures formulations [13].

Angle of Repose
The angle of repose is the angle between the pile of powder and the horizontal plan and measures frictions between powder or granules particles [13]. The angle of repose was determined for pure drugs and all the formulations were prepared manually using the funnel and cone method. Initially, pure drugs were passed separately through a funnel fixed above a petri dish, and the height (h) of the powder heap and petri dish diameter were calculated according to the formula: θ = tan −1 h/r.

Compressibility Index and Hausner's Ratio
Bulk and tapped densities were used for the determination of compressibility index and Hausner ratio. The powder was added manually in a graduated cylinder and the surface was leveled to note bulk volume and then tapped 100 times to attain the tapped volume. Bulk density and tapped density were determined from volume values, while compressibility index and Hausner ratio were calculated from bulk density and tapped density [13].

FTIR Analysis
Once all formulations of drugs were formulated, an FTIR analysis was performed according to the standard procedure for possible interaction between drugs and excipients. Pure drug and formulation mixtures were examined by measuring wavenumbers of 4000-400 cm −1 at a room temperature [14] to obtain FTIR spectra of drugs and drugs along with excipients and were checked for possible interactions.

Tablets Preparation
Tablets were prepared by the direct compression method [15]. Initially, all ingredients were weighed, then geometrically mixed with polythene bags and lubricants, and finally passed twice through 60-mesh sieves for thorough mixing. Manually, the mixture of the clarithromycin layer was put into the die cavity (13.15 mm) of a single-punch tableting machine and compressed. Then, the esomeprazole layer was added and compressed into bilayer tablets individually. Pilot batches of 140 tablets were prepared for each type of formulation for further characterization. The hardness of tablets was kept constant at 5-10 kg/cm 2 .

Physical Quality Control Tests
Various physical quality control tests were performed according to standard procedures [15]. General appearance, shape, thickness, diameters, hardness, friability, and weight variation test.

General Appearance and Shape
The general appearance of tablets was observed with naked eyes and was found elegant. The shape was checked with a magnifying lens.

Diameter and Thickness
The diameter and thickness of 10 tablets randomly selected from each batch were determined using a Vernier caliper. Each tablet's diameter was recorded as mean ± SD [16].

Hardness
Hardness was evaluated with a hardness tester for 10 tablets selected for each batch randomly and average hardness was calculated as mean ± SD in units of kg/cm 2 [17]. In the hardness tester, a tablet was placed and breaking force was noted from the recorder, and then the average hardness of 10 tablets was calculated.

Friability Test
Friability was determined on 10 tablets with a friabilator that rotated at 25 rpm for a rate of 4 min and then, after 100 revolutions, tablets gained weight. Initial weight was measured as W1 and final as W2. Then, friability was calculated as percent and mean ± SD [11].

Weight Variation Test
Ten tablets of each batch were weighed, and the average weight was noted as mean ± SD [18].

Floating Behavior Swelling Behavior
When tablets came in contact with water, polymeric materials started swelling in the tablets; then, all tablets from each batch were taken and placed in 0.1 N HCl 25 mL at 37 ± 0.5 • C and stirred at 25 rpm. Weighed tablets (W o ) were wiped gently with filter paper to remove water on the surface and reweighed (W t ) [19]. Then, water uptake or swelling index was calculated as follows:

Tablet Density
The floating density of tablets is a very important parameter to be considered for the floating behavior of tablets, as a tablet can float when its density is less than 1.004 g/cm 3 . Tablets' volume was calculated according to the formula (v = πr 2 h), and tablets' mass was determined accordingly. The density of formulations was determined for each batch according to the formula (ρ = m/v) [11].

Buoyancy
These tablets had gas-generating material and when came in contact with water, CO 2 was produced inside the tablets that floated on the surface. USP Method-II (paddle method) was used to determine tablet buoyancy/floating. A total of 0.1 N HCl (900 mL) was added to the flask of the apparatus with a rotation speed of 50 rpm and the temperature was maintained at 37 ± 0.5 • C for 24 h. Tablets' total floating time and floating lag time were calculated [20].

Chemical Assay
A chemical assay for all formulations was performed according to a validated method [21]. Randomly, ten tablets were taken from each batch and crushed to powder, and then powder equivalent to 250 mg of Clarithromycin was taken into a 100 mL flask containing 0.1 N HCl. A total of 5 mL of this solution was taken in a 100 mL volumetric flask and diluted with 95 mL of 0.1 N HCl and filtered. Samples were analyzed spectrophotometrically at 276 nm. Powder equivalent to 20 mg of Esomeprazole was taken and added to 100 mL 0.1 N HCl solution and dissolved. A total of 5 mL of this solution was taken in a 100 mL volumetric flask, diluted with 95 mL of 0.1 N HCl, and filtered. Samples were analyzed spectrophotometrically at 284 nm [14,22].

Drug Release Study
USP Method-II was used for the dissolution test, which was carried out initially in the 0.1 N HCl solutions for 6 h and then using the phosphate buffer (pH 7.4) for the next 18 h. The experiments were performed in a pharma test dissolution apparatus (Hamburg, Germany), with a rotation speed of 75 rpm and a dissolution medium temperature of 37 ± 0.5 • C. At specified time intervals, 5 mL samples were taken and a replacement volume of dissolution medium was added. After filtration, samples were separately spectrophotometrically analyzed at a fixed wavelength for clarithromycin (276 nm) and esomeprazole (284 nm). The drug release was calculated from the respective standard curve of each drug [23].

Drug Release Kinetic
First-order (ln (100 − W) = ln100 − K 2 t), zero-order (W = K 1 t), and power-law kinetic model (M t /M ∞ = Kt n ) [24] were used to obtain the drug release mechanism from cumulative drug release data of all the formulations.

Dissolution Profile Comparison
Differences and similarities between reference and tested formulations were determined by applying the difference and similarity factor [25].

Statistical Analysis
Data were analyzed using GraphPad Prism 7 software (GraphPad Software, Inc., La Jolla, CA, USA). All data are presented as the means ± standard deviation (SD) and were first checked for normality using the D'Agostino-Pearson normality test.
The comparison between dissolution profiles of tested formulations and reference formulation comparison was performed using a Paired t-test. A * p < 0.05 was considered significant.

Flow Characteristics
The flow properties to obtain an easy-to-produce product were determined according to the standard procedure. All tablet formulations were found to have good to excellent flow characteristics as the values of the angle of repose ranged from 26.4 ± 0.18 to 30.0 ± 0.06 • , the compressibility index from 11.28 ± 0.02 to 13.16 ± 0.01%, and the Hausner ratio from 1.12 ± 0.02 to 1.14 ± 0.18 [22,[26][27][28][29].
The results of the flow characteristics are summarized in Table 2.

FTIR Study
To check the computability of the drug with the excipients, an FTIR analysis was performed according to the specified protocol. Clarithromycin (Active Pharmaceutical Ingredient) ( Figure 1A) showed a specified spectrum similar to that of its formulation (F1) ( Figure 1B), thus indicating the lack of any interaction. ratio from 1.12 ± 0.02 to 1.14 ± 0.18 [22,[26][27][28][29].
The results of the flow characteristics are summarized in Table 2.

FTIR Study
To check the computability of the drug with the excipients, an FTIR performed according to the specified protocol. Clarithromycin (Active Ph Ingredient) ( Figure 1A) showed a specified spectrum similar to that of it (F1) (Figure 1B), thus indicating the lack of any interaction.  Similarly, esomeprazole (API) (Figure 2A) and its formulation (F1) spectra ( Figure 2B) shared similarity and the functional groups' positions were intact in both spectra.
Our results were in agreement with previous studies conducted using an FTIR analysis [30].  Our results were in agreement with previous studies conducted using an FTIR analysis [30].

Physical Quality Control Tests
Physical quality-control tests were applied according to the specified protocols. All the tables appeared flat and smooth. The controlled-release floating bilayer tablets' thickness ranged from 3.530 ± 0.11 to 3.560 ± 0.139 mm, the diameter from 13.151 ± 0.0748 to 13.155 ± 0.0057 mm, the hardness from 6.56 ± 0.268 to 6.80 ± 0.189 kg/cm 2 , the friability from 0.02 ± 0.081 to 0.06 ± 0.262, and the weight from 671.6 ± 0.98 to 674.0 ± 1.45 mg.
These results were in agreement with other authors [31] and have been reported in Table 3.

Swelling Behavior
According to the literature, all tablets must have a density lower than that of the gastric fluid (1.004 g/cm 3 ) to float over the gastric content [32]. In this sense, the density of all controlled-release floating tablets was less than (1.004 g/cm 3 ). The water uptake ratio to the swelling was shown by the polymeric material that retained some water. Our current formulations swelled up to 89.90% of the original size due to the hydrophilicity of the polymeric materials, particularly Carbopol 934 ( Figure 3) [33].

Physical Quality Control Tests
Physical quality-control tests were applied according to the specified protocols. All the tables appeared flat and smooth. The controlled-release floating bilayer tablets' thickness ranged from 3.530 ± 0.11 to 3.560 ± 0.139 mm, the diameter from 13.151 ± 0.0748 to 13.155 ± 0.0057 mm, the hardness from 6.56 ± 0.268 to 6.80 ± 0.189 kg/cm 2 , the friability from 0.02 ± 0.081 to 0.06 ± 0.262, and the weight from 671.6 ± 0.98 to 674.0 ± 1.45 mg.
These results were in agreement with other authors [31] and have been reported in Table 3.

Swelling Behavior
According to the literature, all tablets must have a density lower than that of the gastric fluid (1.004 g/cm 3 ) to float over the gastric content [32]. In this sense, the density of all controlled-release floating tablets was less than (1.004 g/cm 3 ). The water uptake ratio to the swelling was shown by the polymeric material that retained some water. Our current formulations swelled up to 89.90% of the original size due to the hydrophilicity of the polymeric materials, particularly Carbopol 934 ( Figure 3) [33].

Floating Behavior and Density
All the controlled-release bilayers showed good floating behavior due to the presence of a floating agent, e.g., sodium bicarbonate, which started floating once it came into contact with the simulated gastric fluid (0.1 N HCl pH 1.2 at 37 ± 0.5 • C). The floating lag time ranged from 21 to 25 s. The total floating time was noted for 24 h and all formulations showed a total floating time >24 h. The density was found to be less than 1.004 g/cm 3 .
The results are shown in Table 4 and are in perfect agreement with other authors [11].

Drug Release
Both clarithromycin and esomeprazole were released for 24 h from their respective polymeric controlled-release floating bilayer tablets (F1-F3), thus extending the drug release rate (Figure 4). In particular, F1 released 95.55% of the clarithromycin and 90% of the esomeprazole, F2 released 96.76% and 96.78%, and F3 97.86% and 98.34%.    The drug release rate was extended by polymers, but because Eudragit RS 100 is a pH-dependent polymer, it affected the release by changing the pH from acidic to alkaline. F1 (Carbopol ® 934P and Eudragit RS100) reduced the drug release with respect to F2 (only Eudragit ® RS 100), while F3 (Carbopol ® 934P) delayed the release.
We hypothesized that the extended drug release rate could be ascribed to the polymer Carbopol ® 934P, as it was also reported in the previous work that Carbopol ® 934P extended the Tramadol release rate when used as a rate-controlling agent [33].

Content Uniformity
The content uniformity for each batch was determined, and it was noted that the clarithromycin percent purity ranged from 98.89 ± 0.087 to 101.23 ± 0.026% and that of the esomeprazole ranged from 99.54 ± 0.049 to 101.99 ± 0.023% (Table 5). These results were found within acceptable limits according to the United States and European Pharmacopeia [34].

Drug Release Mechanisms
The drug release mechanisms were determined by applying first-order, zero-order, and power-law kinetic models ( Table 6). The results of the first-order kinetic model showed that the model was best fitted in F4 as it was an immediate release formulation, while the zero-order kinetic model was followed by the F1 to F3 formulations and F4 did not follow the zero-order kinetic model for both the clarithromycin and esomeprazole, and these results are in similarity with other authors [24]. The clarithromycin release data were fitted into the power-law kinetic model and the R 2 (regression equation) values ranging from 0.9189 to 0.9896 showed linearity in kinetics. Meanwhile, the n (drug release exponent) values ranged from 0.7863 to 0.9356, demonstrating that the drug was released by anomalous non-Fickian diffusion. The clarithromycin released from F1 with an n value of 0.9356 was closer to 1, which indicated that this formulation was approaching ideal zero-order kinetics. The reference standard n value was 0.3987, indicating that it did not follow a power-law kinetic. In the case of the esomeprazole, the R 2 value ranged from 0.9645 to 0.9854, showing linearity, while the n value ranged from 0.7234 to 0.9653, showing that the drug was released by anomalous non-Fickian diffusion. Formulation F1 released the esomeprazole with an n value near 1 showing an ideal kinetic, i.e., zero-order. Its reference formulation n-value was 0.412, indicating that it did not follow a power-law kinetic. These results fell within the acceptable range (n-value 0.5 to 1) [24], as observed for losartan potassium [24].

Dissolution Profile Comparison
The dissolution profiles of the tested formulations (F1, F2, and F3) and reference formulation (F4) were compared separately by applying the difference factor f1 and similarity factor f2 ( Table 7). The difference factor value ranged from 24.453 to 38.431, while the f2 values ranged from 18.39 to 43.532. These results were not within the acceptable limit of f1 and f2, 1-15 and 50 to 100, respectively [25].

Test Statistics
The results showed that there was no similarity between the tested formulations profiles and the reference profile (Table 8).

Conclusions
In our research, the effervescent controlled-release bilayer tablets of clarithromycin and esomeprazole were successfully developed and characterized for various parameters. In a buoyancy study, it was found that tablets started floating in a very short time, about 20-24 s, and floated for 24 h. An in vitro dissolution was performed to know about drug release patterns. The polymeric material extended the drug release rates up to 24 h and might be used as a once-a-day (OD) tablet. The drug was released by anomalous non-Fickian diffusion or case-II zero-order kinetics almost near to ideal zero-order kinetics. The percent purity of both drugs was within the USP acceptable limits. The dissolution profile of the tested and reference tablets and the f1 and f2 values were not in the acceptable range. The statistic was applied to the dissolution profiles of the tested and reference formulations, and no similarity was noted between the dissolution profiles.
These polymeric bilayer floating tablets might lead to patient compliance, reduce side effects, and minimize dosage frequency with zero-order drug release kinetics. Funding: Abdulhakeem S. Alamri would like to acknowledge Taif University for support, No. TURSP (2020/288). Syed Mohammed Basheeruddin Asdaq wishes to express his gratitude to AlMaarefa University in Riyadh, Saudi Arabia, for providing support to do this study.

Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.

Data Availability Statement:
Requests to access the datasets should be directed to the corresponding authors.