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ORIGINAL RESEARCH Table of Contents   
Year : 2010  |  Volume : 21  |  Issue : 1  |  Page : 72-83
Studies on development of controlled delivery of combination drug(s) to periodontal pocket

1 Department of Pharmaceuticals, Jaipur National University, Jagatpura, Jaipur, Rajasthan, India
2 Department of Pharmaceutics, Pranveer Singh Institute of Technology, Kalpi Road, Bhauti, Kanpur - 208 020, Uttar Pradesh, India

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Date of Submission11-Dec-2008
Date of Decision29-Mar-2009
Date of Acceptance01-Oct-2009
Date of Web Publication27-Apr-2010


Aim: The aim of this study to develop the controlled delivery of combination drug(s) to periodontal pocket.
Materials and Methods: In the present investigation mucoadhesive gel formulations were prepared using carboxy methylcellulose (CMC), methylcellulose (MC), hydroxyethylcellulose (HEC), polyvinylpirrolidone (PVP), polycarbophil (PC), and poloxamer. Each formulation was characterized in terms of polarizing light microscopy, gelation, gel melting, hardness, compressibility, adhesiveness, cohesiveness, syringeability, adhesion to a mucin disk, rheological studies, drug release, and antibacterial activities. Addition of CMC and PVP to the gel favored hexagonal phase formation. The gelation temperature was decreased linearly with an increasing concentration of drug(s), whereas, the melting temperature increased with the concentration of drug(s). Increasing the concentrations of each polymeric component significantly increased formulation hardness, compressibility, adhesiveness, mucoadhesion, and syringeability, yet a decreased cohesiveness. Increased time of contact between the formulation and mucin significantly increased the required force of detachment. Drug release from all formulations was non-diffusion controlled and significantly decreased as the concentration of the polymer was increased, due to the concomitant increased viscosity of the formulations and the swelling kinetics of PC, following contact with the dissolution fluid.
Result: Antibacterial studies revealed that a gel with 30% HEC had a growth inhibition zone on agar with all three strains.
Conclusion: Formulations containing HEC exhibited superior physical characteristics for improved drug delivery to the periodontal pocket and are now the subject of long-term clinical investigations.

Keywords: Bioadhesive polymers, controlled release, metronidazole, doxycycline, periodontal diseases

How to cite this article:
Tiwari G, Tiwari R, Rai AK. Studies on development of controlled delivery of combination drug(s) to periodontal pocket. Indian J Dent Res 2010;21:72-83

How to cite this URL:
Tiwari G, Tiwari R, Rai AK. Studies on development of controlled delivery of combination drug(s) to periodontal pocket. Indian J Dent Res [serial online] 2010 [cited 2022 Aug 11];21:72-83. Available from:
Periodontal disease is a localized inflammatory response due to infection of a periodontal pocket arising from the accumulation of subgingival plaque. Untreated periodontitis results in the loss of the supporting structures of the tooth through resorption of the alveolar bone and loss of periodontal ligament attachment. Clinically, as the disease progresses, the periodontal pocket, which is somewhat deeper than the sulcus of a healthy tooth, gets deeper with further destruction of the tooth's supporting structures, often resulting in tooth loss. The association of gram-negative anaerobic species with the pathogenicity of periodontal disease has been well-documented. [1],[2] As these bacteria are indigenous to the oral microbiota, their elimination may be difficult, and the probability of repopulation of the periodontal pockets and recurrence of infection following the administration of therapy, is high. In addition, there are numerous inflammatory mediators with bacterial and host origins that contribute to local periodontal destruction and become part of the pathogenesis of the disease. [3]

The local delivery of antimicrobial therapy to periodontal pockets has the benefit of putting more drugs at the target site while minimizing exposure of the total body to the drug. [4] Pocket irrigation has been found to reduce microbial levels and provide some improvement in the clinical parameters, but the response to this therapy has been mixed and the therapy requires daily professional or patient administration for best results. [5] The lack of drug retention in the periodontal pocket is probably the chief reason for these mixed results. The attractiveness of treating periodontal disease using the sustained release of antimicrobial agents in the periodontal pocket is based on the prospects of maintaining effectively high levels of the drug in the gingival crevicular fluid (GCF) for a sustained period of time to produce the desirable clinical benefits of attachment level gain, pocket depth reduction, and reduction in bleeding on probing. In addition, a local delivery device should have high patient acceptance and a method of application acceptable to the dentist's practice.

In the present work, metronidazole and doxycycline with different antibacterial spectra are proposed to be formulated as a combination therapy to include a broader antibacterial therapy, which is effective against both aerobic and anaerobic periodontal microflora. Simultaneous use of metronidazole and doxycycline is suggested to be effective against a wide range of periodontal pathogens, as doxycycline attains seven times more concentration in GCF as compared to the other doxycycline derivatives. The most potent doxycycline for collagenase inhibition is a broad-spectrum antibiotic, which inhibits both Gram-positive as well as Gram-negative organisms, including the beta-lactamase producing strains, which occur predominantly in deep periodontal pockets. [6] Metronidazole is active against obligatory anaerobic periodontal flora, that is, Porphyromonas gingivalis, Prevotella intermedia, and other black pigmenting microorganisms, is widely used systemically and locally for periodontal indications. Thus, the objective of this study was to optimize a stable, bioadhesive periodontal gel for simultaneous extended release of doxycycline and metronidazole using selected cellulose, PVP, poloxamer, and polycarbophil polymers either alone or in combination.

   Materials and Methods Top


MTZ and DOX were obtained as a gift sample from SEIMENS Laboratories (Gurgaon, India) and Welcure Drugs and Pharmaceuticals (New Delhi, India). Crude pig gastric mucin was purchased from Sigma (St. Louis, MO, USA). Hydroxyethylcellulose (HEC), carboxymethylcellulose (CMC), and methylcellulose (MC) were received from Dolder Switzerland) and polycarbophil (Noveon AA-1) was obtained as a gift from B.F. Goodrich (Cleveland, OH, USA). Poly(oxyethylene)poly(oxypropylene) block co-polymer (Poloxamer 407), was a kindly gifted by BASF (Lutrol F 127 ) Wyandotte Corporation, (Cheshire, UK). Agar and polyvinylpirrolidone (PVP) were obtained from Merck Company (Germany). All other chemicals were of analytical grade and purchased from Merck.


Preparation of bioadhesive gels containing metronidazole and doxycycline

Hydroxyethylcellulose, MC (5, 10, 20, and 30% w/w), and poloxamer 407 (10% w/w) were dissolved in the appropriate weight of phosphate buffered saline (PBS, pH 6.8, 0.03 M) using a mechanical stirrer. This gel was transferred onto an ointment slab, and onto this PC (1, 5% w/w) and metronidazole along with doxycycline (5%, w/w; particle size, 63 mm) were successfully and thoroughly mixed [Table 1]. PVP, CMC (5, 10, 20, and 30% w/w), and poloxamer 407 (10% w/w) were dissolved in phosphate buffered saline (PBS, pH 6.8, 0.03 M). PC (1, 5% w/w) and metronidazole along with doxycycline (5%, w/w; particle size, 63 mm) were mixed in this gel [Table 1]. Following removal of air under vacuum, formulations were either characterized as described a little later in the text, or on some occasions, were stored at 48C in grade 2 amber glass ointment jars overnight, prior to analysis.

Polarizing light microscopy

Gel samples were examined under a polarizing light microscope (Nikon, Melville, NY) using an l compensator to study the existence of birefringence under crossed polarized light, employing a magnification of x 100. The lamellar, cubic, and hexagonal phases were identified according to the classification established by Rosevear. [7]

Gelation and gel melting

Gelation and gel melting were assessed using a modification of the Miller and Donavan technique. [8] A 5 ml aliquot of gel was transferred to the test tubes, immersed in a water bath at 4C, and sealed with aluminum foil. The temperature of the water bath (Haake Phoenix c25P, Karlsruhe, Germany) was increased in increments of 0.5C and left to equilibrate for one minute at each new setting. The samples were then examined for gelation, which should have occurred when the meniscus would no longer move upon tilting through 90. The gel melting temperature, the temperature at which a gel starts flowing upon tilting through 90, was recorded.

Mechanical characterization of bioadhesive formulations

The mechanical properties of all formulations under examination were examined using the texture profile analysis. [9] Formulations were transferred into McCartney (30 ml volume, grade 2 clear glass) bottles to a fixed height, taking care to avoid the introduction of air into the samples. Texture profile analysis was performed using a Stable Micro Systems Texture Analyzer (Haslemere, Surrey, UK), in a texture profile analysis mode in which the analytical probe (10 mm diameter) was twice compressed into each sample at a defined rate (2 mm/s) to a depth of 15 mm. A delay period (15 s) was allowed between the end of the first and the beginning of the second compression and all analyses were performed at least in quadruplicate. From the resultant force-time plots, several mechanical parameters may be derived. [9] These include:

  • Product hardness (force required to attain a given deformation) was measured by a Rotovisco (RV3) cone and plate viscometer.
  • Compressibility or spreadability (the force required to deform the sample during the compression). A 24-hour- old gel (1 g) was pressed between two horizontal plates of 20 cm 2 , of which the upper one weighed 46.36 g and a 200 g weight was placed over it at ambient temperature. A circle of 5 mm in diameter was made and the diameter of the gel was measured after five minutes. [10]
  • Cohesiveness (the ratio of the area under the force-time curve produced on the second compression cycle to that on the first compression cycle, where successive compressions are separated by a defined recovery period).
Examination of the work of syringeability of drug(s) containing bioadhesive formulations

The syringeability of each formulation was determined using the texture analyzer. In brief, formulations were transferred into identical plastic syringes to a constant height (3 cm). The content of each syringe was fully expressed using the texture analyzer in compression mode and the resistance to expression was determined from the area under the resultant force-time plot. Increased work of syringeability was denoted by increased areas under the curves. All measurements were performed at least in quadruplicate.

Evaluation of the mucoadhesion of metronidazole-doxycycline containing formulations

The mucoadhesion of the formulations under investigation was determined using the texture analyzer in tension mode, as follows: Mucin disks were prepared by compression of a known weight of crude pig gastric mucin (250 mg) in a Carver press for 30 seconds using a compression force of 10 tons. These were then attached to a cylindrical probe (length 5 cm, diameter 1 cm) using a double-sided adhesive tape. Metronidazole-doxycycline (MTZ-DOX) containing formulations were packed into McCartney bottles and centrifuged (3000 g for 5 minutes) to remove any entrapped air. The mucin disks were then placed in contact with the gel formulations and a downward force was applied (0.1 N) for a range of times (0.5, 1, 2, 3, and 4 minutes). The probe was removed vertically at a constant upward speed (1 mm/s) and the force required to detach the mucin disk from the gels was measured as the peak value in the force-time plot.

Rheological studies

Rheological measurements have been carried out by using two different instruments, depending on the sample viscosity. Low and high viscosity samples were measured by using Rheometrics RFS2 and Rheometrics RMS800 rheometers (Rheometrics, Possum Town, NY, USA), respectively. Parallel plates (25 mm diameter; 1.5 mm gap) and couette geometries (1 mm gap) were used. Both oscillatory and monodimensional steady shear flow have been considered. Oscillatory measurements were carried out at a low amplitude (within the linear viscoelastic region) with an angular velocity (v) of between 0.1 and 100 rad/s. Measurements were conducted at four different temperatures, namely 10, 20, 30, and 37C. According to the Bohlin theory that considers flow as a cooperative phenomenon, the coordination coefficient z was calculated from the slope of the curve obtained by plotting the elastic modulus (G') versus v in a log-log plot. The sol-gel transition temperature (T c ) was calculated by 'time cure tests' obtained by plotting elastic (G') and loss (G") moduli as the functions of temperature. Determinations were performed at 1 Hz and at a low amplitude, the temperature range was 4-40C and the temperature ramp was 1C/minute. The viscosity had been measured at a low shear rate (0.1-10 s -1 ), in order to avoid slipping effects at the wall surface, possibly caused by high shear rates.

In vitro release of MTZ-DOX

In vitro release of MTZ-DOX from the bioadhesive gel formulations was performed (in triplicate) using a 37 ml Franz diffusion cell. [11] The diameter of the donor cell was 26 mm and the dissolution medium was PBS. The diffusion cell was water jacketed at 37C; 1.5 g of the gel was transferred to the Durapore HVLP membrane (0.45 μm) of the vessel. At predetermined time intervals, 2 ml samples of the receptor fluid were taken and analyzed for MTZ and DOX spectrophotometrically at 318 nm and 273.8 nm, respectively. The medium was replaced after each sampling.

Drug(s) release data analysis

Data obtained from dissolution studies were fitted to the general release equation (Eq. (1)) proposed by Gurny et al. [12] using logarithmic transformations and least squares regression analysis.


the percentage of drug(s) released at time t,

K = a constant incorporating structural and geometric characteristics of the delivery system

n = the release exponent.

Statistical analysis

The rate of release of drug(s) (k), the time required to dissolve 50% of the drug(s) (t 50% ), the dissolution efficiency, [13] the correlation coefficient of different kinetic models of release data, and the mechanical properties were evaluated statistically using a one-way ANOVA. Post-hoc statistical analysis of the means of individual groups was performed using Fischer's least significant difference test (P < 0.05 denoting significance) using SPSS computer software (Version 10, 1999).

Antibacterial activity tests

Bacterial strains and growth conditions P. gingivalis ATCC 33277, S. aureus ATCC 25923, and  Escherichia More Details coli ATCC 25922, were used in this study. S. aureus and E. coli represented Gram-positive and Gram-negative bacteria, respectively, and were used as reference strains for antibacterial activity testing. P. gingivalis was subcultured weekly on supplemented blood agar sBA, trypticase soy agar, supplemented with yeast extract 1 mg/ml, vitamin K 1 5 μg/ml, hemin 5 mg/ml, and 5% (v/v) human blood. [14] The other bacteria were cultured on Mueller-Hinton agar (MHA; Merck, Germany) slant at 378C. To standardize the cells, the reference strains were grown to reach the log phase and then the suspension was adjusted to 25% transmittance at an OD 560 corresponding to approximately 10 8 colony-forming units/ml, and this was used further for antibacterial activity testing.

Susceptibility tests

Antibacterial activity was screened by the cylinder plate method. [15] Plates containing sBA or MHA agar were brushed using sterile swabs with 25% transmittance test solitary organisms (P. gingivalis, S. aureus, and E. coli). Solution of optimized gel (Sample 1) was prepared at a concentration of 20 mg/300 μl DW. Solutions of the reference antibiotics were prepared at a concentration of 30 μg/300 μl DW. These samples were sterilized by filtration through wetting-agent-free cellulose acetate 0.2 μm filter (Sartorius, Germany). Reference antibiotic solution of 300 μl or the test sample solution of 300 ΅l was placed in a cup on the agar plate. P. gingivalis on sBA was incubated in an anaerobic glove box (Thermo Forma, Germany) with 80% N 2 , 10% CO 2, and 10% H 2 at 37C for 72 hours, whereas, S. aureus and E. coli on MHA were incubated in an aerobic incubator (Heraeus B5060 E, Germany) at 37C for 24 hours. After the incubation period, the diameter of the inhibition zone was measured with an antibiotic zone reader (Fisher Scientific TM , USA) and recorded in millimeters. Sample 1 was selected for further testing of the minimum inhibitory concentration (MIC). MICs were determined in a microtiter assay [16] by inoculation of 100 μl of P. gingivalis suspended in supplemented BHI (sBHI; yeast extract 5 mg/ml, vitamin K1 5 μg/ml, and hemin 5 μg/ml, final concentration 5 x 10 5 colony-forming units/ml) in a 96-well microtiter tray with two-fold serial dilutions, by adding 100 μl of a solution of Sample 1 or control antimicrobial agents (doxycycline, metronidazole). The final concentrations of test sample 1 were 32, 16, 8, 4, 2, 1, 0.5, 0.25, 0.125, and 0.625 mg/ml, and for the antimicrobials were 8, 4, 2, 1, 0.5, 0.25, 0.125, 0.0625, 0.03125, and 0.0156 μg/ml. The plates were incubated anaerobically for 72 hours. The MICs were recorded with the lowest concentration at 90% inhibition. Minimum bactericidal concentrations (MBCs) were determined by culturing on sBA for 48 hours. The percentage of inhibition was expressed by the following equation:

Percentage inhibition

For studies of the kinetic death rate of Sample 1, a cellular suspension (100 μl, 10 5 colony forming units/ ml) of P. gingivalis was inoculated into sBHI. To the test sample 1, aqueous solution, final concentration 2-8 mg/ml, was added, and the mixture was incubated at 37C for 0, 2, 5, 9, 24, 48, and 72 hours. At designated intervals, 100-μl portions were taken, diluted, and dropped on to the sBA. The plate was incubated for 48 hours, and the colonies were counted.

   Results and Discussion Top

Polarizing light microscopy

Polarizing photographs of gel without CMC and PVP and a gel containing 10% CMC and 5% PVP are shown in [Figure 1]. The photographs show a dark background in the case of plain gel, whereas, some fan-like structures are observed in the polarizing photograph of the P 5 C 10 formulation.

Incorporation of drug(s) did not affect the liquid crystalline phase of gel; it remained in the cubic phase. Incorporation of CMC and PVP did affect the phase structure where it converted from the cubic phase into the hexagonal phase. However, an increase in the concentration of PVP did not produce any change in the phase structure. It was revealed that the plain gel was in the cubic phase, which transformed to the hexagonal phase after the addition of CMC and PVP. For PVP, the type of structures obtained in the presence of a selective solvent appeared to be a function of the volume fraction of the polar/apolar component. This was attributed to the ability of the macromolecule blocks to swell to a different extent (based on the amount of solvent available) in the respective solvents and to thus modulate the interfacial curvature and resulting structure. The interfacial curvature was defined as positive when the interface bent toward the apolar domains, that is, the micelles were surrounded by the polar domains, confining the apolar domains inside them, and vice versa. In the cubic phase, the interfacial curvature was highly positive because of the spherically shaped micelles. The normal hexagonal phase had been obtained at a high content of CMC (10%) and at 5% PVP, because of decreased solvation of the PVP blocks. PVP absorbed water from the system and as a result less water was available for CMC, which caused the transformation of the cubic phase to the hexagonal phase.


The effect of drug(s) concentration on gelation and gel melting is shown in [Figure 2]. The gelation temperature was lowered in the presence of drug(s) and decreased linearly with its increasing concentration, whereas, the melting temperature increased with the concentration of drug(s). Physically, gel formation is related to micellar packing and volume fraction. Researchers have attributed gelation to the dehydration in the micelle core, [17] a change in the micellar volume [18] or a decrease in the critical micelle concentration, and an increase in the aggregation number. [19] The finding that drug(s) lowered the gelation temperature is similar to the result reported by Esposito et al. [20] This feature is tentatively explained by a facilitation of the interaction between the hydrophobic portion of the polymer molecules, which could disrupt the micellar structure and increase the entanglement of micelles. At a higher concentration of drug(s), lowering of the critical micellar concentration facilitates closer packing of micelles, which means that more energy is needed to break the gel structure. The gel structure is thought to remain unaltered with temperature until an excessively high temperature causes the destruction of the gel structure. At higher temperatures, the gel undergoes dehydration, but excessive hydrogen bonding and closely packed micelles restrict the destruction of the gel structure. As the concentration of the HEC increases and concentration of MC decreases, the gel structure becomes more closely packed, with the arrangement in a lattice pattern. In turn, the disruption of the lattice melting of the gel occurs at higher temperatures.

Mechanical characterization of bioadhesive formulations

In this study, the mechanical properties of the candidate formulations for the treatment of periodontal disease have been determined. Texture profile analysis (TPA) defines the mechanical parameters in terms of hardness, compressibility, and adhesiveness, properties that will affect the ease of product application into, and retention within, the periodontal pocket, respectively. TPA also allows an estimation of the extent of structural reformation following product administration (cohesiveness), a factor which will influence product performance. Therefore, in this regard, TPA is an applicable technique for the characterization of formulations designed for application to the periodontal pocket. Increased product hardness, compressibility, and syringeability are associated with increased concentrations of HEC or CMC and PC in each formulation. Each of these parameters describes the resistance of each formulation to compression, and therefore, reflects alterations in product viscosity, as previously recognized. [9],[20] Statistical interactions have been observed between the effects of the polymeric components on these mechanical properties, which are due to unexpectedly great hardness, work of compression, and syringeability, associated with formulations containing 30% (w/w) HEC or CMC and 5% PC. These formulations contain the greatest proportions of suspended, unswollen particles, and the greater resultant semi-solid properties account for the unexpected compression properties.

Product cohesiveness has been reported to describe the spatial aspects of structural reformation following product compression. [9] As the PC content was increased, the mass of suspended solids increased. Subsequently, the semi-solid nature of the product increased, which in turn decreased the formulation cohesiveness. Decreased product cohesiveness associated with increased concentrations of HEC or CMC was a function of increased product viscosity, as the viscoelastic properties of these formulations would be affected by this parameter. [9] The statistical interaction term reflected the unexpected greater reduction in the cohesiveness of formulations containing higher concentrations of each polymer, which was again due to the proportionally greater semi-solid character of these formulations. The mechanical parameters of each formulation are presented in [Table 2]. Increasing concentrations of HEC or CMC and/or PC, significantly increased formulation hardness, compressibility, and adhesiveness, yet, they decreased the cohesiveness. Typically maximum and minimum hardness, compressibility, and adhesiveness were associated with formulations containing 30% (w/w) HEC or CMC and 5% (w/w) PC, and 5% (w/w) HEC or CMC and 1% (w/w) PC, respectively. In the case of cohesiveness, the reverse was observed, that is, maximum and minimum values being associated with formulations containing 5% HEC or CMC and 1% PC, and 30% HEC or CMC and 5% PC, respectively. With the exception of formulations containing 5% (w/w) HEC or CMC and 1% PC, HEC containing formulations exhibited significantly greater hardness, adhesiveness, and compressibility than their counterparts (% w/w) containing CMC.

The syringeability of each formulation is presented in [Table 3]. Once more, increasing concentrations of each polymeric component (HEC/CMC and/or PC) significantly increased the force required to expel each formulation from a periodontal syringe over a fixed distance. Formulations containing (5% w/w) HEC or CMC displayed statistically similar values of work of syringeability (P.0.05), whereas, the work of syringeability of the formulations containing 30% HEC significantly exceeded those formulations containing 30% (w/w) CMC.

In this investigation, the adhesive properties of the candidate formulations were examined using two methods, namely texture profile analysis, which described the work required to remove a polymeric probe from the test formulation, and also by evaluation of the detachment force required to overcome the adhesive bond between each formulation and a compressed mucin disk. [21] In addition, for all formulations, the time of contact with the mucin disk significantly influenced the strength of the mucoadhesive bond. This could be explained by hydration of the mucin, due to the uptake of moisture from each formulation, which in turn allowed interpenetration of the polymeric chains in the mucin and those in each formulation. [22] The exceptions from these observations were associated with formulations containing 5% (w/w) CMC in which cohesive bond failure occurred. The effect of HEC on the bioadhesive properties of formulations containing PC was significantly greater than that of CMC. The possible mechanisms causing this disparity were highlighted within the statistical interaction term between the polymeric components, with respect to the adhesiveness and detachment force. Yet again, in these interactions, formulations containing 5% (w/w) PC and 30% (w/w) HEC or CMC displayed unexpectedly large numerical values of adhesiveness and detachment forces. It was reported that the bioadhesive properties of formulations containing PC increased as the number of uncharged carboxylic acid groups increased. [23] Therefore, formulations containing a higher concentration of HEC or CMC and 5% (w/w) PC possessed the greatest masses of unswollen, uncharged particles, and subsequently, these formulations demonstrated the greatest adhesion to both the mucin and the polymeric probe.

Rheological studies

In this study, a series of preliminary results on the rheological characterization of poloxamer-based gels is presented [Table 4]. This study was performed in order to define the general rheological behavior of these relatively novel materials and to provide information on their structure, as a function of temperature and for the presence of solubilized guest molecules (i.e., MTZ and DOX). In particular, we determined the sol-gel transition temperature (T o ) by 'time cure tests', the frequency dependence of the elastic modulus G' by 'frequency sweep tests', and the temperature dependence of G' and the z coefficient [Figure 3], [Figure 4] and [Figure 5]. From the analysis of the results obtained by this series of experiments, the following general considerations can be drawn.

  1. [Figure 3] reveals that poloxamer gels are characterized by a sharp transition from a liquid (sol) to a structured (gel) behavior at a well-defined temperature (T c ) determined by the analysis of T versus G' curves. The highest value of T c (218C) has been found in the case of a 25% poloxamer gel, while 20 and 30% gels show a lower T c value [Figure 3].
  2. In all samples, both elastic modulus G' and the coefficient increase as temperature increases [Figure 4] and [Figure 5]. In this regard, it must be noted that G' and z give indications about the structure strength and the structure coordination, respectively.
  3. At temperatures above 15C, the samples show pseudo-plastic behavior, characterized by a typical shear thinning behavior.
  4. The presence of drug(s) causes a shift T c to a lower value (ΔT c = 6.8C) [Figure 3] and concomitant increase of both G' and z values [Figure 5].
Taken together, these results indicate that MTZ and DOX can have a positive effect on both gel structuration and strength. This feature has been tentatively explained by a facilitation of the interactions between the hydrophobic portions of the polymer molecules responsible for the gelation process. This facilitation can be due to the insertion of the planar MTZ and DOX molecule within the polyoxypropilenic fractions.

In vitro drug(s) release kinetics

HEC and/or CMC containing gels, following dissolution in PBC or water, respectively, formed primary gels, the viscosity of which was dependent on the concentration of the polymers. [Figure 6] and [Figure 7] show the effect of different types of bioadhesive polymers and their increasing concentrations on the release of drug(s) from gel formulations. PC is a cross-linked derivative of polyacrylic acid, which does not dissolve, but exhibits swelling, the extent of which is dependent on the amount of available water present in the formulation, that is, the water not associated with the dissolved polymer. Therefore, in formulations containing 30% (w/w) HEC or CMC, the amount of free water is decreased and the extent of swelling of the PC in these formulations is decreased in comparison to the formulations containing 5%(w/w) HEC or CMC. In formulations containing 5% (w/w) HEC or CMC, PC existed primarily in swollen state. In all formulations MTZ and DOX were present in a suspended form. The state of the PC in each formulation was responsible, at least in part, for many of the observations of this study. Decreased drug(s) release from formulations containing increased concentrations (30% w/w) of either HEC or CMC could be described as the corresponding increase in product viscosities that are associated with increased polymer concentrations. Decreased release, associated with increased concentrations of PC, in formulations containing 5% (w/w) HEC or CMC could also be explained by the concomitted increase in product viscosities, following swelling of this polymer within the formulation. Drug release from the CMC systems was greater than from their HEC counterparts and was due to greater viscosities of HEC/PC formulations. Increased PC concentrations primarily decreased the release of drugs. The release of drug(s) from formulations that contained 30% (w/w) HEC and 5% (w/w) PC was significantly greater than those containing 30% (w/w) HEC and 1% (w/w) PC. These observations could be explained by the relative degrees of swelling of PC in each formulation. Product swelling was greater for formulations containing HEC, in comparison to those containing CMC, due to the greater masses of unswollen PC. Without doubt, as a result of excessive swelling of this polymer, during dissolution testing, partial product disintegration occurred for formulations containing 30% (w/w) HEC and 5% (w/w) PC. Therefore, the surface areas of these formulations increased, which in turn, increased the rate of drug release. The time required for the release of drug (t 50% ) from each formulation is shown in [Table 5]. The time required for 50% drug release from formulations containing HEC was significantly greater than from those containing comparable concentrations (% w/w) of CMC and PVP. DE after 24 hours (DE 24 %) [13] and t 50% were used to compare the drug release characteristics of different formulations [Table 5].

Drug(s) release data analysis

In order to investigate the mechanism of drug release from controlled delivery formulations, the values of the kinetic parameters n, K, and R from Eq. (1) have been calculated [Table 5] and [Table 6]. The overall viscosity is increased with polymer concentration. Thus, a reduction in the drug release rate is most probably due to decreased rates of penetration of the dissolution fluid into the higher viscosity products. PVP and CMC formulations showed Higuchi release kinetics, which are too difficult and not suitable from a mechanical point of view. The gels containing 10% HEC need low work of syringeability [Table 3], but the drug release lasts only 24-36 hours [Figure 6]. However, products with 30% (w/w) HEC not only have suitable mechanical properties, but show sustained release profiles for 46-58 hours [Figure 6]. An increase in the polymer concentration of HEC increases the k value more effectively than MC. Increasing concentrations of PVP from 5-30% in gels containing CMC, decreases the k and t 50% . The constant concentration of PVP increases the CMC from 5-30%, and also increases the k and t 50% [Table 5]. Following application of the general release equation (1) to the release data of all formulations, it is observed that there is a release exponent (n) that ranges from 0.5 to 1.0 [Table 5], indicating non-Fickian drug transport. The mechanism of drug release from the gels has been previously reported as diffusion-controlled (19, 20), that is, where n = 0.5. Therefore, it is suggested that other mechanisms, for example, polymeric swelling and or dissolution, contribute to the complex release characteristics of drugs from formulations under the current investigation.

Antibacterial activity

Antibacterial activities are summarized in [Table 7]. Briefly, Sample 1 had a growth inhibition zone on agar with all three strains. Interestingly, doxycycline afforded similar zones of inhibition with respect to E. coli and S. aureus [16.4 and 23.7 mm for doxycycline, 18.2 and 18.4 mm for Sample 1]. However, with P. gingivalis, doxycycline was considerably more potent [45 mm for doxycycline, 24.7 mm for Sample 1]. The E. coli and P. gingivalis used were susceptible to doxycycline with MICs of 0.2-2 μM and MBCs of 1-8 μM. P. gingivalis was susceptible to metronidazole with an MIC of 0.7 μM and an MBC of 1.4 μM. At the critical concentration (0.14 mM), during incubation times of 10 minutes, 1 hour, and 2 hours, the numbers of P. gingivalis decreased dramatically with no viable counts after 2 hours.

   Conclusion Top

This study has described the design and development of mucoadhesive, syringeable gel systems for application to the periodontal pocket. The mechanical and mucoadhesive properties and release profiles of MTZ and DOX from several candidate formulations, particularly those containing HEC and MC, will indicate a possible advantageous role in the treatment of periodontitis. The gels have been characterized by a peculiar rheological behavior, as a function of polymer concentration, temperature, and presence of drug(s), which possess the appropriate properties to serve as an intra-pocket drug(s) delivery system for periodontal therapy. Long-term clinical evaluation of these formulations is currently ongoing.

   Acknowledgment Top

The authors gratefully acknowledge the Central Drug Research Institute, Lucknow (India) for providing the bacterial strains. The study was financially supported by the Department of Pharmaceutics, Pranveer Singh Institute of Technology.

   References Top

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Correspondence Address:
Gaurav Tiwari
Department of Pharmaceuticals, Jaipur National University, Jagatpura, Jaipur, Rajasthan
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Source of Support: Department of Pharmaceutics, Pranveer Singh Institute of Technology, Conflict of Interest: None

DOI: 10.4103/0970-9290.62814

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  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7]

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7]

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