Palatable Levocetirizine Dihydrochloride Solid Dispersed Fast-Dissolving Films: Formulation and In Vitro and In Vivo Characterization

One of the most important issues for bitter-tasting drugs such as levocetirizine dihydrochloride (LCD) is the production of palatable dosage forms. LCD also has a delayed onset of action following oral administration. In this study, solid dispersed fast-dissolving films (FDFs) of LCD using the solvent casting method for oral application were prepared and evaluated. The FDF is composed of HPMC as the film forming polymer and different types of superdisintegrants (sodium starch glycolate, croscarmellose sodium, or crospovidone). FDF containing crospovidone showed the highest percentage release of the drug (100.54% ± 1.47 within 3 min.) and was chosen for fabricating into palatable solid dispersed FDFs using different ratios of gelatine. The results of Raman and FTIR revealed that the drug's crystalline structure has been disrupted, and the drug has intermolecular hydrogen bonds with gelatine. The solid dispersed FDF (LF-7), which contained the drug in the form of a 1 : 1 solid dispersion with gelatine, showed a rapid in vitro disintegration (25 seconds) and a burst release of the drug (99.22% ± 2.22 within one min). The in vivo studies were conducted on human participants and showed a significant (p < 0.05) reduction in disintegration time (9.43 ± 2.16 sec.) and higher taste masking ability of the solid dispersed FDF (LF-7) compared to the nonsolid dispersed FDF (LF-4). The stability studies indicated that the prepared FDF remained stable over three months. Overall, FDFs of levocetirizine dihydrochloride with a palatable and rapid onset of action were developed to relieve allergic symptoms.


Introduction
Te oral route bears various advantages over others for drug administration with some restrictions that arise from administering solid oral dosage forms. Low bioavailability, delayed onset of action, difculty in swallowing or chewing, and taste masking have led to the development of advanced dosage forms suitable for more patient compliance, such as fast-dissolving flms (FDFs) [1,2]. Oral fast-dissolving flms are composed of hydrophilic polymers, which rapidly dissolve or disperse once it comes in contact with the buccal cavity or tongue. FDFs are instantly hydrated by the saliva, adhere to the oral mucosa, and subsequently release the drug for absorption through the highly vascularised oral mucosa. Tis transmucosal absorption results in rapid onset of action with local and systemic efects and bypasses the frst-hepatic metabolism or degradation in the gastrointestinal tract, leading to improved bioavailability [3,4]. In addition, the formulation of FDFs by using natural or synthetic polymers such as gelatine and hydroxypropyl methylcellulose (HPMC) with appropriate sweeteners and favoring agents is sufcient to achieve good mouth feel and taste masking [5].
LCD is a selective, nonsedative, and long-active antihistamine drug with less side efects. It was found that in adults, with the administration of 5 mg of oral solution and tablets of LCD, the peak plasma concentrations were achieved in 0.5 and 0.9 h, respectively [6]. LCD has a bitter taste and is classifed as the BCS-III class under the biopharmaceutical classifcation system [7]. Tus, many tastemasking techniques are adapted to reduce or eliminate bitterness by obscuring the unpleasant taste of drugs or preventing dissolved drugs from interacting with taste buds [8,9]. Some taste-masking techniques were used in order to mask LCD bitter taste such as complexation with HP-βCD, solid dispersion with mannitol, and ion exchange resins [10][11][12][13][14]. It was reported that the bitter taste of the drugs could be masked by using solid dispersion with a suitable polymeric carrier [15]. Te bitter substances are bound to an excipient or trapped in a particulate, reducing their concentration in the oral cavity and preventing their release.
Gelatine is a natural protein, with both positive and negative charged groups, hydroxyl groups, and hydrophobic groups. It has the ability to form complexes that are stabilized by electrostatic interactions, hydrogen bonds, and to a lesser extent by hydrophobic interactions [16]. Gelatine is used conventionally as an excipient in capsules and tablet formulations to ease swallowing and as a taste-masking agent. It has been reported that gelatine forms a gel on the surface of the tablets to mask the bitter taste of the drugs and, as a flm forming agent, it rapidly dissolves, producing a smooth mouth feel [15].
In this study, authors aimed to develop solid dispersed fast-dissolving flms of levocetirizine dihydrochloride by using gelatine as a dispersing agent for LCD and hydroxypropyl methylcellulose as a flm forming agent. Furthermore, superdisintegrants, sweeteners, and favoring agents were used to formulate a palatable LCD solid disperse FDFs, thereby achieving a fast onset of action to relieve the symptoms associated with allergic conditions.

Materials.
Levocetirizine dihydrochloride (LCD) was obtained as a gift sample from Modern Pharmaceutical Company, Sana'a, Yemen; HPMC and propylene glycol were purchased from Sigma-Aldrich, UK; sodium starch glycolate (SSG), croscarmellose sodium (CCS), crospovidone (CP), and gelatine were purchased from SD Fine Chemicals, India; sucrose, vanilla, and citric acid were purchased from Loba Chemie, India. All chemicals used were of analytical grade. Table 1 shows the compositions of the seven FDFs of LCD in which HPMC is used as the flm-forming polymer, propylene glycol as the plasticizer, and three types of superdisintegrants at a concentration of 6% w/w: SSG, CCS, and CP. Citric acid stimulates the saliva, sucrose as a sweetener, and vanilla as a favoring agent. Te solvent casting method was used to prepare these flms. HPMC was dispersed in 20 ml of hot deionized water and stirred with a magnetic stirrer until the gel was formed. For formulations LF-1, LF-2, LF-3, and LF-4, the drug is dissolved with the other excipients in deionized water using a magnetic stirrer. Ten, the drug solution of each formula was added separately to the HPMC gel containing propylene glycol and thoroughly stirred for about 30 min to ensure a uniform distribution of the drug solution. Ten, they were left aside to remove air bubbles and then cast into a Petri dish (5.5 cm in diameter). Tey were left to dry for 24 h and were carefully removed from the Petri dish, checked for any imperfections, and cut into 1 cm 2 flms as each flm contained 5 mg of LCD.

Preparation of LCD Fast-Dissolving Films.
Te solid dispersions at weight ratios of 1 : 0, 1 : 0.75, and 1 : 1 (w/w) of LCD: gelatine, were obtained by the solvent evaporation method. Te calculated amounts of LCD were added to the dissolved gelatine aqueous solutions and left to dry for 24 h at room temperature to obtain solid flms, which were then crushed and dissolved in deionized water with the same excipients used for formulation LF-4. Ten, the solid dispersed drug solutions were added to the HPMC gels and followed the same procedures as for preparing the FDFs to obtain the formulations LF-5, LF-6, and LF-7.

Characterization of the Solid Dispersed LCD with Gelatine
2.3.1. Fourier Transform Infrared Spectroscopy. Te FTIR spectra for pure LCD, gelatine, and the solid dispersions of LCD with gelatine at 1 : 0.5, 1 : 0.75, and 1 : 1 w/w were analysed by using an FTIR spectrophotometer (PerkinElmer Spectrum, version 10.6.2) over the wavelength number range of 4000-450 cm −1 to investigate if there was any interaction in solid-state between LCD and gelatine.

Raman Spectroscopy.
A portable Raman spectrometer has a wavelength of 785 nm with a resolution of 8-10 cm −1 , and a laser-class of Mira P advanced class 3B was used to investigate the crystalline state of LCD. A few milligrams of the powder samples of pure drug, gelatine, and solid dispersions of LCD with gelatine at weight ratios of 1 : 0.5, 1 : 0.75, and 1 : 1 were closed in glass vials. Ten, the spectra of the samples by the laser power of about 100 mW room temperature over the spectral range of 2300-400 cm −1 using Mira Cal P software were recorded.

Tickness, Weight Variation, and Folding Endurance.
Te thickness of each formulated FDF was measured at nine diferent positions on the flm (the centre and eight corners) using a micrometer screw gauge. Te weight uniformity was determined by taking the individual weights of 10 randomly selected 1 cm 2 flms from each formulation using a calibrated

Surface pH Measurement.
Tree 1 cm 2 flms of each formulation were allowed to dissolve in 5 ml of saliva simulated phosphate bufer (pH 6.8) at room temperature, and the pH was measured by bringing a combined glass electrode into contact with the solution and allowing it to equilibrate for 1 min. [18].

Drug Content Uniformity.
Te seven formulae were evaluated for drug content uniformity by dissolving 3 flms of each formula using phosphate bufer solution (pH 6.8) in a 50 ml volumetric fask that were diluted to the mark with the bufer and fltered through a 0.45 μm membrane flter. Te drug absorbance was measured spectrophotometrically at a maximum wavelength of 232 nm against a blank [19]. Te concentrations were calculated from the equation of the standard calibration curve of LCD (y � 0.0311x−0.0089, R 2 � 0.9995).

In Vitro Disintegration Time.
One flm of each formulation was put separately in a Petri dish containing 10 ml of deionized water and was agitated smoothly and continuously. Te time at which the FDFs started to disintegrate or break was recorded in seconds as disintegration times [18].

Moisture Absorption and Loss.
Tree flms from each formula were weighed separately (W1) and kept inside a desiccator containing silica gel for measuring moisture loss. For moisture absorption, three accurately weighed flms from each formula were placed in a desiccator containing a saturated solution of aluminium chloride and keeping the humidity inside it at 75 ± 5% RH. Te samples were kept for three days, and then the flms were reweighed (W2), and the moisture loss and uptake were calculated using the following equations, respectively [20]. . Te study protocol was explained, and written informed consent was obtained from all participants in the studies. Te participants were asked to administer a pure powder (5 mg) in their mouths to assess the degree of bitterness and register their scores as 0: not bitter, 1: slightly bitter, 2: bitter, 3: moderately bitter, and 4: strongly bitter. Te mouth was thoroughly rinsed with water, and a time of 30 min was kept between each trial. Te same participants were asked to apply the same procedures by the administration of the selected flms. Te time required in seconds for the starting disintegration of the flms and the irritation efect, if any, were recorded [21]. Te results of palatability were analysed for statistical signifcance at p < 0.05 by using a one-paired Student's t-test.

Stability Studies.
Te stability studies were performed as per ICH guidelines for the selected formula LF-7. Te flms were wrapped in aluminium foil, packaged in an amber screw glass bottle, and stored in a desiccator at 45°C with a humidity of 75 ± 5% RH for three months. Te flms were evaluated after one and three months for weight, thickness, disintegration time, dug content, and dissolution studies [22].

Results and Discussion
Seven formulations were made using 3% w/w of HPMC as a flm-forming polymer, and each flm dose contained 5 mg of LCD. Ten, the formulation that showed the high percentage of cumulative drug release in a short time, LF-4, was subjected to modifcation in order to obtain palatable FDFs. In this study, a solid dispersion technique Te Scientifc World Journal was used, utilizing gelatine as a dispersing agent for LCD at a weight ratio (w/w) of drug to gelatine of 1 : 0.5, 1 : 0.75, and 1 : 1. Te addition of a greater amount of gelatine results in a reduction in the quality of the flms. So, the addition of the drug in the form of solid dispersion with gelatine to the compositions of the formulation LF-4 at these weight ratios was suitable to produce uniform, smooth, and fexible flms.  at 1743.80 cm −1 and at 1602.84 cm −1 assigned to the stretching vibration of phenyl nucleus skeletal [23,24]. In addition, the absorption bands were at 1318.03 cm −1 , 1135.69 cm −1 , and 757.52 cm −1 due to stretching vibrations of C-N, C-O, and C-Cl, respectively [6]. Gelatine consists entirely of amino acids joined together by amide linkages to form a linear polypeptide [5]. Te FTIR spectra of gelatine (Figure 1(b)) shows a broad band at 3265.04 cm −1 attributed to NH and OH stretching vibrations, an absorption band at 1629.58 cm −1 due to the stretching vibration of amide carbonyl in amide I and at 1522.99 cm −1 due to NH and CN vibration of groups in amide in II [16]. As shown in fgure (Figures 1(c)-1(e)

Raman Spectroscopy.
Raman spectroscopy is an easy, rapid, and useful analytical technique for the investigation of the crystal forms of pharmaceutical compounds and excipients [27]. Te diferences can be observed between Raman spectra from diferent crystal forms of a compound or between crystalline and amorphous forms of pharmaceutical compounds [28]. Raman spectroscopy can be utilized to monitor the structural phase transition of a drug from crystalline to amorphous as it dissolves in the polymer [29]and for the assessment of the drug's solid-state physical stability and recrystallization kinetics during various storage conditions [30].
Te Raman spectroscopy of LCD, gelatine, and solid dispersions of them at 1 : 0.5, 1 : 0.75, and 1 : 1 w/w is depicted in Figure 2. Te observed Raman spectra of LCD confrms its crystalline nature, as evidenced by the number of distinctive and intense peaks situated between wavenumbers 2300-400. However, Raman spectra of gelatine showed difused peaks, indicating its amorphous nature. As shown in Raman spectra of solid dispersions, the characteristic peaks of LCD are nearly absent in solid dispersions, and they show the gelatine pattern, particularly at a solid dispersion of 1 : 1. Te crystalline structure of the drug is disrupted when dissolved in gelatine, and the loss of crystallinity indicates that there are intermolecular interactions between the drug and gelatine [29,31].

Characterization of LCD Fast Dissolving Films.
Te results of the evaluated parameters of the prepared FDFs of LCD are presented in Table 2.
Te folding endurance values for all the prepared LCD FDFs were found to be more than 300 times, which gives a good indication of the fexibility and the ability of the flms to withstand rupturing.

Surface pH Measurement.
Te surface pH of the FDFs of each formula was investigated in order to predict the possibility of any side efects occurring due to the change in the pH of the oral saliva, as acidic or alkaline pH may cause irritation to the oral mucosa. Te formulations exhibited a surface pH between 5.69 ± 0.18 and 5.96 ± 0.12, which was close to the salivary pH range (6.5-6.8) [32].

Drug Content Uniformity.
Te results of the percentages of drug content uniformity were between 96.06 ± 1.40 and 102.68 ± 1.31 which were within the acceptable range in all prepared formulae.

In Vitro Disintegration Time.
From the results obtained in Table 2 and Figure 3, it could be seen that all the prepared FDFs were rapidly disintegrated in less than one min, but LF-7 containing gelatine and CP exhibited shorter disintegration times of 25 ± 2.00 sec compared to the others and hence was expected to obtain a fast release of the drug.

Moisture Absorption and Loss.
Moisture absorption and loss were measured to ensure the flms' integrity under humid and dry conditions, respectively. Te loss of water content may contribute to the brittleness of the flms, whereas the gain of water may cause sticky flms [5]. Te moisture uptake results for the prepared flms ranged between 5.11% ± 0.13 and 6.88% ± 0.10, and moisture loss results ranged between 4.17 ± 0.07% and 6.90 ± 0.14 which could be attributed to the presence of hydrophilic polymers [33].

In Vitro Dissolution Studies.
In vitro release studies for all of the prepared formulations were determined using saliva simulated fuid as a release medium (pH 6.8). Te cumulative percentage release of LCD per minute is depicted in Figure 4. It was found that all the prepared formulae exhibited a high percentage of the drug released after one min (Table 2), which could be attributed to the use of HPMC, which has a burst efect just presenting the flms in the dissolution medium [34]. Te time required to release approximately 100% of the LCD, on the other hand, varied depending on the composition of the FDFs. Films formulated without the superdisintegrant LF-1 showed 101.51% ± 2.51 within 9 min. Formulae that contained three types of superdisintegrants, LF-2, LF-3, and LF-4, showed percentages of the drug released of 100.62% ± 2.82, 99.26% ± 0.63, and 100.54% ± 1.47 within 7, 15, and 3 min, respectively, which may be due to the diference in their mechanisms of hydration capacity that facilitate the disintegration of the flms either by absorbing water rapidly followed by swelling (SSG), wicking and swelling (CCS), or by capillary action (CP). It was found that FDFs containing SSG and CCS exhibited longer times in the drug released compared with FDFs containing CP, which may be  attributed to the tendency of SSG and CCS to swell and may form viscous gel layers around the flms when fully hydrated that act as barriers for further rapid release of the drug. In contrast to SSG and CCS, CP is highly porous in nature, resulting in the production of porous flms that exhibit virtually no tendency toward gel formation, even when using in high concentrations [35][36][37]. Gelatine flms produce a smooth mouthfeel and rapidly dissolve. Tis is clearly seen when FDFs are fabricated by using solid dispersions of the drug with gelatine. Furthermore, increasing the ratio of gelatine to LCD from 0.5 in LF-5 to 1 in LF-7 increases the porosity of the flm [35][36][37], which subsequently results in the fast release of LCD (LF-5 97.22% ± 1.40, LF-6 101.71% ± 3.00 within 2 min, and LF-7 99.22 ± 2.22 within one minute). Table 3 depicts the mean scores of the selected formulations for the taste masking ability of the bitter taste of LCD. All the selected FDFs contained sucrose and vanilla. Te drug powder has a strong bitter taste, as indicated by the participants who gave it a mean score of 4. However, FDFs containing LCD as solid dispersions with gelatine exhibited signifcantly lower scores for taste masking ability (LF-5 and LF-6; p < 0.05) and (LF-7; p < 0.001) compared to LF-4. Te success of producing palatable FDFs of LCD was made more pronounced by the incorporation of LCD as a solid dispersion with gelatine at a weight ratio of 1 : 1 into FDFs, which indicated that G-protein coupled receptors are shielded from the efects of LCD since the latter is dispersed uniformly across the gelatine crust [38]. In addition, efective taste masking can also be attributed to the favours. It was observed that rapid in-vivo disintegration times of 13.71 ± 3.96, 8.14 ± 3.38, and 9.43 ± 2.16 sec (Table 3) compared with the in-vitro disintegration times of 54 ± 2.00, 30 ± 2.00, and 25 ± 2.00 sec for LF-1, LF-4, and LF-7, respectively ( Figure 5). Te fast in vivo disintegration may have been facilitated by the tongue's pressing movement against the palate to retain flm attachment. Another possible explanation for the shortened in vivo disintegration time is the incorporation of citric acid into the FDFs, which promoted saliva secretion in the buccal cavity and contributed to the faster disintegration of the FDFs [12,39].

Stability Studies.
Te results of stability studies of the selected palatable FDFs of LCD LF-7 are presented in Table 4. During the storage periods, there were no diferences in drug content, disintegration time, or drug release. Te flms also showed satisfactory fexibility, weight variation, and thickness. Te results revealed that LF-7 was stable during the storage periods for the three months at 45°C and a humidity of 75 ± 5% RH [40].

Conclusion
In conclusion, levocetirizine dihydrochloride was incorporated as solid dispersions with gelatine into HPMC fastdissolving flms. At a 1 : 1 weight ratio, the flms disintegrated rapidly in less than 30 seconds, approximately completely   releasing the drug within one minute and remaining stable over the storage period. Te bitter taste was masked efectively by using the solid dispersion method. So, a palatable and rapid onset of action FDFs of levocetirizine dihydrochloride was obtained to relieve the allergic symptoms of allergic rhinitis and upper respiratory tract infammation.

Data Availability
Te data supporting the conclusion of this study will be provided by the corresponding author upon request.

Conflicts of Interest
Te authors declare no conficts of interest.