International Journal of Drug Development and Research

Keywords

Floating microspheres, Levofloxacin hemihydrate, Helicobacter pylori, drug entrapment efficiency.

INTRODUCTION

Historically, oral drug delivery systems are the most popular drug delivery system but these systems have some, limitation such as, patient incompliance due to frequent drug administration, undesirable side effect due to fluctuating plasma drug level, inability to maintain adequate drug concentration in plasma for therapeutic effect, larger dose than required dose [1]. This limitation can be overcome by modifying existing drug delivery systems (DDSs). An appropriately designed sustained release (SR) or controlled release DDS can be a major step toward solving the problem associated with conventional DDSs[2]. Oral controlled release (CR) dosage forms (DFs) have been developed for the past three decades due to their considerable therapeutic advantages [3]. However, this approach has not been suitable for a variety of important drugs, characterized by a narrow absorption window in the upper part of the gastrointestinal tract, i.e. stomach and small intestine. This is due to the relatively short transit time of the DF in these anatomical segments. Thus, after only a short period of less than 2-3 h, the CRDF has already left the upper gastrointestinal tract and the drug is released in non absorbing distal segments of the gastrointestinal tract. This results in a short absorption phase that is often accompanied by lesser bioavailability. The medications that are included in the category of narrow absorption window are mostly associated with improve absorption at the jejunum and ileum due to their enhanced absorption properties, e.g. huge surface area [4]. It was suggested that preparing narrow absorption window drugs in a unique pharmaceutical DF with gastro retentive properties would enable an extended absorption phase of these drugs [5]. The major objectives of the study are to formulate and evaluate the levofloxacin floating microspheres with the help of hydroxypropyl methyl cellulose (HPMC K4M) and release-retarding hydrophobic polymer ethyl cellulose to control the release of highly water soluble levofloxacin hemihydrates for the systemic as well as local delivery for eradication of H. Pylori.

MATERIALS AND METHODS

PREPARATION OF FLOATING MICROSPHERES

Floating Microspheres were prepared by a Nonaqueous Solvent Evaporation method. HPMC K4M and EC (14cps) were mixed in the mixture of acetone and ethanol at 1:1 ratio. The slurry was slowly introduced into 50 ml of liquid paraffin containing 1% Tween 80 while being stirred at 1000 rpm using mechanical stirrer equipped with five bladed propellers at room temperature. The solution was stirred for 2 h and allowed the solvent to evaporate completely and filtered by using filter paper (Whatman filter paper). The microspheres obtained were washed repeatedly with petroleum ether (40-60oC) until free from oil. The collected microspheres were dried at room temperature and subsequently stored in desiccators. Same procedure was repeated for all the batches [6].

EVALUATION OF FLOATING MICROSPHERES

Size distribution and morphology

The floating microspheres were examined by optical and scanning electron microscopy (SEM). A freshly prepared suspension of microspheres in 0.1% Tween 80 was examined on an optical microscope. The size of the microspheres was measured using a photo microscope [7]. Around 100 particles from each formulation were measured and the observed data of each formulation are presented in Table 1.

The surface morphology of microspheres was visualized by scanning electron microscopy. The samples for SEM were prepared by lightly sprinkling the microspheres particles on a double adhesive tape which stuck to an aluminum stub. The stubs were then coated with gold to a thickness of about 300oA using a sputter coater.

These samples were than randomly scanned and photomicrographs were taken which are shown in Fig. 2 (A & B).

Microspheres of the drug with combination of ethyl cellulose and HPMCK4M were porous, rough, and grossly spherical. The surface topography reveals that the microspheres were highly porous due to the rapid escape of the volatile solvents during formulation. Very less particulate matter of the drug were seen on the surface of the microspheres indicating uniform distribution of the drug in the polymeric network. The microspheres are retained in the stomach by virtue of their buoyancy due to the pores and hydrophobic nature of ethyl cellulose.

Flow Properties

The flow properties of all the formulations were found out by measuring the angle of repose and compressibility index. The results are shown in table 2. The values of angle of repose were between 230 to 340, which are within the normal acceptable range of 200 to 400. The porous microspheres thus showed reasonably good flow potential. The values of Compressibility index (I) was in the range 20 to 28, indicating good flow characteristics of the microspheres. This also implies that the microspheres are nonaggregated. Thus they can be easily handled and filled into a capsule8, 9. Therefore, capsules loaded with microspheres can be suggested as a floating micro particulate drug delivery system. Moreover the soft gelatine capsules easily absorb water and disintegrate and do not hinder with the floating capability of the microspheres [10, 11].

Estimation of drug incorporation efficiency and % yield

The values of total drug content and % incorporation efficiency are shown in table 3. High incorporation efficiencies are seen with higher concentrations of ethylcellulose. Comparison of total incorporation efficiencies is shown in Fig.2. F-8 shows the highest incorporation efficiency (89.06%) while F-3 shows the least (74.86%).

In vitro buoyancy studies

The purpose of preparing floating microsphere was extend the gastric residence time of a drug, the in vitro floating behavior was investigated in the acidic medium containing a small amount of surfactant Tween 20 (0.02% w/v), agitated with a paddle at 50 rpm was used to simulate the wetting action of gastric fluid under movement. The results are shown in table 3. In vitro buoyancy studies reveal that in spite of stirring the dissolution medium for more than 12 hours about 58-82.47% of microspheres were still continued to float without any apparent gelation, thus indicating that microspheres exhibit excellent buoyancies which can be attributed to the pores and lower density of polymer12. Comparison of % buoyancy of different formulation is shown in Fig.5.

The percentage buoyancies increase with increase concentration of ethyl cellulose. So the microspheres having higher polymer (Ethylcellulose) concentrations were more buoyant (F8; 82.47%) than those with lower polymers (ethylcellulose) concentrations (F5; 58.64%).

In vitro drug release studies

Dissolution studies on all the eight formulations of Levofloxacin hemihydrates floating microspheres were carried out using a USP XXIII Type II i.e., Paddle Type dissolution apparatus. As the microspheres floated in the stomach and released the drug, SGF (pH 1.2) was used as the dissolution medium. A combination of polymer was used for the current study to design a perfect gastro retentive delivery system which released most of the drug in upper part of gastrointestinal tract. As the amount of ethyl cellulose used in the preparation was increased the release of the drug was decreased due to hydrophobic nature of ethyl cellulose13.

The In vitro drug release data for each of the formulations is shown in tables 4 to table 11. The cumulative percent drug release after 8 hours was found to be 90.527±0.0420, 88.874±0.0036, 89.866±0.0027, 86.065±0.0361, 91.662±0.0063, 85.569±0.0021, 88.874±0.0047, 87.221±0.0052% for the formulations F-1 to F-8 respectively. The initial fast release may be due to the release of surface adsorbed drug. It indicates a period that the drug release is prolonged over a period of 8 hours in case of Levofloxacin hemihydrates in which ratio of HPMCK4M and EC were 1:9. It may be concluded from this in vitro drug release study that the release rate can be controlled by varying the polymer: polymer ratio and the dosage form could be designed to give the release in a controlled fashion at the desired site. As for Levofloxacin hemihydrates, the site of absorption is upper GI tract, the formulation F-8 can serve the needs of a controlled release in upper GIT.

DATA ASSESSMENT FOR OPTIMIZATION OF ORMULATIONS: EFFECT OF POLYMER ON % BUOYANCY

Positive value of 1 (9.80) showed that the factor X1 (quantity of EC) have positive effects on % buoyancy (Y). As the value of this factor increases, there will be increase in the % buoyancy as observed from results. Same thing was found with factor X2 (quantity of tween-80) as positive value of 2 showed a significant positive effect on % buoyancy. On the other hand factor X3(quantity of drug) showed negative effect on % buoyancy as observed from the results. Value for o was found 72.39 for % buoyancy optimization. Mathematically, response (dependent variable) for % buoyancy can be shown by equation- Y=72.39+9.80X1+1.043X2+1.792X3-0.145X1X2- 0.870X1X3-0.2075X2X3-0.09X1X2X3

KINETIC MODELLING

The correlation coefficients for the different drug release kinetic models are shown in Tables 14. Models with the highest correlation coefficient were judged to be the most appropriate model for the dissolution data14, 15. The results of in vitro drug release studies were treated with zero order, first order kinetics, Higuchi, Hixson Crowell and Korsmeyer Peppas model.

As clearly indicated in Table 14, the formulations F2.F4, F5, F6, F7 and F8 follow a zero?order release with highest r2 value from 0.9642 to 0.9108 respectively. Only formulation F5 (r2=0.9178) follows first order release pattern

In our experiments, the in vitro release profiles of drug from all the formulations could be best expressed by Higuchi’s equation, as the plots showed high linearity (R2= 0.9231 to 0.9929 ). To confirm the diffusion mechanism, the data were fitted into Korsmeyer Peppas model. All formulations F1 to F8 showed high linearity (R2= 0.9669 to 0.9946), with slope (n) values ranging from 0.5013 to 0.9890. This indicates that coupling of diffusion and erosion mechanism so called anomalous diffusion. It might be concluded that the drug release is controlled by more than one mechanism i.e. diffusion coupled with erosion mechanism.

STABILITY STUDIES OF OPTIMIZED FORMULATION

The optimized formulation (F 8) was subjected to stability studies at a room temperature / 60 % RH and 400C / 75% RH for one month. The optimized formulation was evaluated for their appearance, drug content, % buoyancy after 12 hrs and invitro release study. Negligible change was seen in different physicochemical parameters at a room temperature as well as 400C/75 % RH. .( see table 16 & 17) There was no significance difference in in-vitro release after one month stability study at both room temperature and accelerated conditions which was further confirmed by similarity factor (f2) calculation(Table 18 & 19).

RESULTS AND DISCUSSION

All formulations were subjected to evaluation parameter studies like % buoyancy, entrapment efficiency, % yield and drug release profile and following results were found: The % buoyancy of all the formulation (F1-F8) was found to be in the range of 58.64-82.5. The formulation F2 and F8 were found to have best % buoyancy i.e. 82.5 and 82.47 respectively. The drug entrapment effiency of all the formulation (F1-F8) were found to be in the range of 74.86-89.06. The formulation F6 and F8 were found to have best drug entrapment effiency i.e. 82.53 % and 89.06 % respectively. The % yields of all the formulation (F1-F8) were found to be in the range of 50.571- 59.76. The formulation F7 and F8 were found to have best % yield i.e. 59.546 and 59.76 respectively. The drug release profiles of all the formulation (F1-F8) were found to be in the range of 85.569±0.0021 - 91.662±0.0361. The formulation F4 and F8 were found to have best % drug released profile i.e. 86.06505±0.0361 and 87.22193±0.0052 respectively. From the above results i.e. % yield, % DEE, % buoyancy and % drug released, the formulation F8 was consider as an optimized formulation.

CONCLUSION

Multiunit floating drug delivery system (microspheres) for levofloxacin hemihydrate was prepared by emulsion solvent evaporation method with the help of hydroxypropyl methyl cellulose (HPMC K4M) and release-retarding hydrophobic polymer ethyl cellulose (14 cps). Prepared formulation showed the acceptable % yield, % DEE, % buoyancy and % drug released. As the ratio of ethyl cellulose increase, the % DEE, % buoyancy increase and % drug released was decreased. Optimized formulation followed the Higuchi kinetics while the drug release mechanism was found to be anomalous types (case II transport) or non- Fickian type, controlled by diffusion through the swollen matrix. In vitro drug release studies showed a biphasic release pattern for all formulations with an initial burst affect which may be attributed to the drug present on the surface. The in vitro release profiles of drug from optimized formulation could be best expressed by Higuchi’s equation. To confirms the diffusion mechanism; the data was fitted intoKorsmeyer Peppas model. The (n) value indicates that drug release followed the coupling of diffusion and erosion mechanism so called anomalous diffusion. Optimized formulation was found to be stable at all stability conditions.

Tables at a glance

Table 1 Table 2 Table 3 Table 4 Table 5 Table 6 Table 7 Table 8 Table 9 Table 10 Table 11 Table 12 Table 13 Table 14 Table 15 Table 16 Table 17 Table 18 Table 19

Figures at a glance

Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11

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