|Year : 2013 | Volume
| Issue : 2 | Page : 99-107
Formulation and evaluation of modified-release effervescent floating tablets of ofloxacin
Sarat Chandra Prasad Malisetty, Ravi Teja Allena, Swetha Sandina, HV Gangadharappa
Department of Pharmaceutics, Jagadguru Sri Shivarathreeswara College of Pharmacy, Jagadguru Sri Shivarathreeswara University, Mysore, Karnataka, India
|Date of Web Publication||26-Jul-2013|
Sarat Chandra Prasad Malisetty
Department of Pharmaceutics, Jagadguru Sri Shivarathreeswara College of Pharmacy, Jagadguru Sri Shivarathreeswara University, Mysore - 570 015, Karnataka
Source of Support: None, Conflict of Interest: None
Aims: Ofloxacin is used as anti-microbial agent. Due to its high solubility in gastric pH, a floating drug delivery system was selected to improve the bioavailability and therapeutic efficacy of the drug. Settings and Design: The purpose of the study was to prepare and evaluate effervescent floating tablets of ofloxacin to prolong its gastric residence and increase bioavailability. Materials and Methods: Drug, semi-synthetic and natural polymers, such as HPMC K4M, Guar gum, Xanthan gum and Chitosan, were used. Sodium bicarbonate and citric acid were used as gas-generating agents and tablet compression was done by direct compression. The prepared tablets were characterized and were evaluated for in vitro floating behavior, swelling index, in vitro drug release studies and release kinetics. Results: Formulation F6 containing xanthan gum and chitosan in a 1:1 ratio attained sustained release for 12 h and drug release observed was about 76.7%. Swelling index was in the range 62.17 ± 1.49% to 194.02 ± 1.05%. Floating lag time was observed in the range 4.11-6.26 min. Conclusion: The in vitro results showed better drug release conditions, supported by follow-up in vivo studies, suggesting that this formulation is advantageous over the current marketed formulation, through increased gastric residence and bioavailability.
Keywords: Chitosan, effervescent floating drug delivery system, HPMC K4M, in-vitro release studies, in-vivo studies, ofloxacin
|How to cite this article:|
Malisetty SP, Allena RT, Sandina S, Gangadharappa H V. Formulation and evaluation of modified-release effervescent floating tablets of ofloxacin. Int J Health Allied Sci 2013;2:99-107
|How to cite this URL:|
Malisetty SP, Allena RT, Sandina S, Gangadharappa H V. Formulation and evaluation of modified-release effervescent floating tablets of ofloxacin. Int J Health Allied Sci [serial online] 2013 [cited 2019 Oct 20];2:99-107. Available from: http://www.ijhas.in/text.asp?2013/2/2/99/115685
| Introduction|| |
An oral tablet is the most preferred route for drug administration because it is more natural and less invasive than other traditional routes. Though it is less invasive, the real challenge is to increase the dosage in the gastrointestinal tract by increasing gastric residence time. Normal gastric residence times usually range between 5 min and 2 h. Gastric emptying is unpredictable in the presence of food and disease conditions, though drugs with a short half-life are eliminated quickly from the stomach. Various oral controlled delivery systems have been designed, which can overcome these problems and release a drug to maintain its plasma concentration for a longer period of time in the stomach. This has led to the development of oral gastro-retentive dosage forms. Gastro-retention is essential for drugs that are absorbed from the stomach, drugs that are poorly soluble or degraded by the higher pH of the intestine, and drugs with absorption, which can be modified by changes in the gastric emptying time. This dosage form improves bioavailability, therapeutic efficacy and may even also allow a possible reduction in the dose because of steady therapeutic levels of a drug, for example, furosemide and ofloxacin. 
The main purpose of a floating drug delivery system is to increase the gastric residence time of the dosage form by generating gas and followed by swelling of the system, which retards the drug release by forming a gel layer around the surface of the system. 
Floating drug delivery systems offers advantages, such as drug with narrow absorption window and required localized action, over other tablet dosage forms of drugs that are absorbed in the stomach, for example ferrous salts and antacids. These floating systems will increases the bioavailability of the drug by floating the dosage form in the stomach for a longer period of time; increased patient compliance is seen because of reduced pill burden. Effervescent floating drug delivery systems can remain in the stomach for long periods and hence can release the drug over a prolonged period of time. These systems are suitable for a narrow absorption window. ,
Ofloxacin is a fluoroquinolone with antibacterial activity, which is effective against both Gram-positive and Gram-negative bacteria. It is used in diseased conditions such as respiratory tract infections. The dose of ofloxacin for adults is about 200-400 mg for 12 h.  Ofloxacin exhibits pH-dependent solubility. The solubility of ofloxacin in water is 60 mg/ml at a pH value ranging from 2 to 5, which falls to 4 mg/ml at pH 7 (near isoelectric pH). 
Ofloxacin floating tablets were prepared by previous researchers using the wet granulation technique by incorporating natural polymers such as Guar gum, locust bean gum and hydroxypropyl methylcellulose (HPMC) K100M as swelling polymers with sodium bicarbonate as a gas-generating agent.  HPMC K4M was used as a floating polymer. 
In the present study, different formulations were formulated in different polymer ratios and evaluated for in vitro buoyancy and gelling studies. In addition, various characterization studies were performed to check the compatibility of the prepared formulation; based on data from in vitro drug release studies, the best formulation was selected for in vivo studies. In vivo studies were carried out in rabbits as an animal model (Sprague-Dawley) and drug concentration in blood was measured by the high-performance liquid chromatography, and pharmacokinetic parameters were calculated.
| Materials and Methods|| |
Ofloxacin was a kind gift sample from Pondchy Pharmaceuticals (Pondicherry, India). Chitosan, Xanthan gum and Eudragit E100 were purchased from Sigma Aldrich (Bangalore, India. HPMC K4M was purchased from Shreeji Chemicals (Mumbai, India). All other chemicals and reagents used were of analytical grade.
Preparation of effervescent floating tablets
The direct compression technique was adopted for preparation of effervescent-type floating tablets by employing polymer types such as HPMC K100M, K4M, Chitosan, Xanthan gum, Guar gum and Eudragit E100. The formulation table of the tablets is shown in [Table 1]. The components were blended for 15 to 20 min according to ascending order of weight and finally with magnesium stearate as a lubricant. Direct compression was done by using Rimek Minipress-1(model-1674; Mumbai, India) machine with flat face punches and dies (12 mm in diameter). 
The integrity and compatibility of ofloxacin and the polymers used in the tablets were studied by Fourier transform-infrared (FT-IR-8400; Shimadzu Co., Tokyo Japan) spectroscopy. Pelletization was done by using a KBr press. The FT-IR spectra were recorded in the wavelength region between 4000 and 400 cm−1 .
Differential scanning calorimetry
About 5 mg of the sample was weighed and crimped into an aluminum pan, and analyzed at the scan range 0°C−300°C at a heating rate of 5°C/min under a nitrogen flow rate of 25 ml/min. It was measured by differential scanning calorimetry (DSC) using Q200 V24.4 Build 116 (Universal V4.7A TA Instruments, New Castle, USA).
Scanning electron microscopy
Morphological details of the tablets before and after dissolution in buffer were determined by scanning electron microscopy (SEM). It was measured using the Joel SEM analysis Instrument (model JSM 840A., Korea, Japan).
A 5-g weight of ofloxacin powder was weighed and gently poured through a short-stemmed glass funnel into a 100-ml graduated glass cylinder.  The volume occupied by granules was read and the bulk density of the powder was determined and measured in terms of g/cm 3 .
Tapped density was determined by USP method II. The tablet blend was filled into the 100-ml graduated cylinder of the tap density tester ETD-1020, which was operated for a fixed number of taps until the powder bed volume reached a minimum. It was measured in terms of g/cm 3 .
Compressibility index and Hausner's ratio
This was measured to assess the property of a powder to be compressed; as such they are measured for relative importance of inter-particulate interactions. Compressibility index was calculated. 
Angle of repose
The circumference of a pile of powder was drawn with a pencil and the height of the pile was measured without disturbing the pile. The radius of the pile was noted down as 'r' cm and calculated.
Twenty tablets were selected randomly in every batch and average weight was calculated. (As per Indian pharmacopoeia, limit ± 5% for 500 mg tablets.) Then the deviation of individual weight values from average weight and standard deviation were calculated.
Crushing strength was determined using an Erweka IHT 100 (Ahmedabad, India). Ten tablets were randomly selected from each batch. In the tablets the crushing strength was additionally transformed to tensile strength. It was measured in terms of Kg. 
Twenty tablets are weighed and placed in a plastic chamber, which was revolved at 25 r.p.m. for 4 min. The tablets are then reweighed to % loss in weight. The friability of the tablets was determined by average hardness and standard deviation was calculated.
Determination of thickness
Thicknesses of five randomly selected tablets from each batch were measured with a digital Vernier caliper. Then average thickness and standard deviation were calculated. Tablet thickness should be controlled within 5% variation from a standard value.
In vitro buoyancy
In vitro buoyancy was determined by visually observing floating lag time; tablets were placed in a 100-ml beaker containing 0.1 N HCl. The time required for the tablets to rise to the surface and float was considered as the floating lag time. The time between tablet placement in the beaker and their buoyancy and total floating duration was recorded. 
The swelling behavior of the tablets was determined in triplicate. Tablets were weighed and placed in a glass beaker, containing 200 ml of 0.1 N HCl, maintained in a water bath at 37 ± 0.5°C for 10 h. The tablets were removed after every 2-h interval up to 10 h and the excess surface liquid was carefully removed with a filter paper and weighed. ,
Five tablets were selected randomly from a batch, weighed and powdered in a mortar. An accurately weighed quantity of powdered tablets equivalent to 100 mg was transferred to a standard flask and the volume was made up to the mark with 0.1 N HCl; the solution was filtered through a 0.45-μm membrane paper. Analysis was done using a spectrophotometric method at 293 nm. 
In vitro release studies
Dissolution test was carried out using the USP apparatus IIElectrolab EDT 08 L (Mumbai, India). A 900-ml volume of 0.1 N hcl was used as the dissolution medium and the paddle was rotated at 50 r.p.m. for 12 h. A 5-ml volume of the sample was withdrawn at predetermined time intervals and 5 ml of fresh medium was replaced to maintain the sink condition. the collected samples were analyzed at 293 nm by UV spectrophotometry. 
In vivo floating studies
The gastric retention property of the effervescent floating formulation F-6 (placebo) was studied in male albino rabbits. Barium sulfate was used as a radio opaque marker in the tablet formulation. The formulation was administered orally to rabbits with 5 ml of water. X-ray pictures were taken at different time intervals, 2 nd , 6 th and 12 th hours.
In vivo experimental studies were performed after approval from the institutional animal ethical committee. The tablets were given in oral administration. The prepared ofloxacin effervescent formulation was compared with commercially available tablets as a reference (Oflox 200 mg tablet). Using the selected formulation F-6 and a reference formulation, in vivo studies were carried out by using rabbits as an animal model (Sprague-Dawley). Rabbits were fasted overnight before administration of dose. The animals were weighed and numbered, and they were divided into four groups each containing six rabbits. The reference drug was administered to the first group. A 200-mg dose of the tablet effervescent formulation F-6 was administered to the second, third and fourth groups. Blood was collected from the ear portal vein at time intervals of 0.5, 1, 2, 3, 4, 6, 8, 10 and 12 h.
The plasma concentration of the drug was estimated using high-performance liquid chromatography validated for efficiency, linearity, accuracy and precision. The estimation was carried out using an ODS, C-18 (250 × 4.6 mm, 5 μm; Phenomonex, Hyderabad, India) column and absorbance was recorded at 293 nm by using a UV detector. The mobile phase was prepared using a methanol: acetonitrile: water solution containing 1.5 g phosphoric acid per liter (5:5:80, v/v/v) and absorbance was recorded at 293 nm with a UV detector by high-performance liquid chromatography. Flow rate was maintained at 0.9 ml/min. Blood containing EDTA (anticoagulant) was centrifuged at 3500 r.p.m. for 15 min. The supernatant was collected and acetonitrile (1 mg/ml) was added to precipitate the proteins. The precipitated proteins were settled by centrifugation at 8000 r.p.m. for 8 min and the supernatant was collected. A 1-ml volume of the collected supernatant was filtered through a 0.45-μm membrane filter and this solution was stored at −20°C until high-performance liquid chromatography analysis.  Plasma concentration-time profiles were evaluated by extra-vascular method of residuals. The following pharmacokinetic parameters were determined using the Kinetica 5.0 software: Cmax and Tmax .
Kinetics and mechanism of drug release
In vitro release was analyzed using kinetic models, and release kinetics were described by employing different equations, such as zero-order,  first-order,  Higuchi,  Hixson and Crowell equation,  and Korsmeyer Peppa's equation. ,,
Stability studies were carried out for optimized patch at 45°C/75% relative humidity in a humidified chamber for 90 days. After 90 days the samples were analyzed for drug content and drug release.
| Results|| |
Compatibility studies by FT-IR
The FT-IR spectra result [Figure 1] indicated that there was no drug-polymer interaction. The IR spectra recorded for ofloxacin and the physical mixture pure ofloxacin showed characteristic peaks at 3423 cm−1 (O-H stretching), 3041 cm−1 (C-H stretching, aliphatic), 2929 cm−1 (C-H, aromatic), 1718 cm−1 (C = O stretching) and 707 cm−1 (O-H deflection). In the formulation, peaks were observed at 3041, 2929, 1724 and 700 cm −1 .
|Figure 1: (a) FT-IR spectrum of pure drug ofloxacin. (b) FT-IR spectrum of the physical mixture|
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Differential scanning calorimetry
The comparative DSC thermograms of pure ofloxacin and physical mixture are represented in [Figure 2]. The DSC thermogram of ofloxacin displayed a characteristic peak at 271.5°C corresponding to its melting point. The drug peak appeared in the thermogram at 269.8°C, confirming the chemical integrity of the drug.
Scanning electron microscopy
The surface morphology of the tablets before dissolution shows that there were no cracks in the tablets. After dissolution the tablets showed cracks, which indicated that drug release might have been by swelling and erosion of the polymer. An SEM photograph is shown in [Figure 3].
|Figure 3: SEM photographs of tablets (a) before and (b) after dissolution|
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the pre-formulation studies of ofloxacin were evaluated for various physical properties and the results are shown in the [Table 2]. The bulk density of powder indicated good packaging character of the tablets. Carr's index was found to be below 15% for all formulations, which indicated acceptable flow properties. Hausner's ratio for all formulations was less than 2%, which also indicated the good flow property and packaging characters of the powders. angle of repose showed that the flow property of the power was excellent and it was within acceptable limits.
Physical evaluation of ofloxacin tablets
Physical evaluation of tablets was studied. The average weight of tablets was found to contain 0.501 ± 0.02 to 0.524 ± 0.03 mg. Hardness was found to be 4.3 ± 0.3 to 4.9 ± 0.3 kg and friability was found to be 0.26 ± 0.19 to 0.82 ± 0.13%. The thickness of the tablets was found to be 4.26 ± 0.02 to 4.99 ± 0.03 mm. The evaluation results show that all the parameters were within acceptable limits.Individual readings of all formulations were tabulated in [Table 3].
In vitro buoyancy
Formulations F-1, F-2, F-3, F-5, F-6 and F-8 showed floating time greater than 12 h and formulations F-4, F-7, F-9 and F-10 showed less floating time when compared with the other formulations because of Eudragit, which was more soluble in pH less than 5, so it was partially disintegrated after 8-10 h; although it disintegrated, it showed good release and its the floating time decreased when compared with the other formulations. Results are shown in [Figure 4].
- Indicated that gas-generating agents help to overcome gravitational force when the tablet is quickly immersed in 2 s.
- Indicated that after 4 min the system floats by gas entrapment in the core, which helps to float the tablet.
- Image (c) showed that after the 12 th hour, tablets tend to float at the top portion, indicating it can float in gastric pH for more than 12 h.
Swelling studies revealed that the F-2 formulation showed more swelling in 0.1 N HCl because of its hydrophobic nature and more gelling properties of Chitosan, and percent swelling observed was 194.02 ± 1.05%, followed by the F-3 formulation, which contained Xanthan gum as a polymer and whose percent swelling was 176.74 ± 1.64%, which was due to the high viscosity of the polymer. Formulation F-4 showed 141.85 ± 2.09% swelling because of Eudragit, which was hydrophilic and disintegrated without much swelling. When Xanthan gum was in combination with Chitosan it showed a percent swelling of about 127.68 ± 1.67%, which was due to hydrophobic Chitosan. Least swelling was observed with formulation F-10, 62.17 ± 1.49%, due to the less viscous Guar gum and hydrophilic Eudragit E100, which helped majorly in disintegration of the dosage form rather than percent swelling. Results are shown in [Figure 5] and [Figure 6].
|Figure 5: (a) Swelling of tablets at the 1st hour (b), at the 8th hour and (c) at the 12th hour|
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In vitro release studies
In vitro release studies showed that formulation F-4 showed 91.4% drug release at the end of the 12 th hour due to the presence of Eudragit, which was soluble in gastric pH, so it showed more release at the 10 th hour itself. F-6 attained a sustained release pattern and its percentage drug release was about 76.7%. Chitosan is a hydrophobic polymer, which showed better gelling properties and helped in the retardation of drug release. In every batch, HPMC K4M was used to reduce the density of the formulation and also it was used as the release-retarding polymer. A comparative graph for formulations F-1-F-10 is shown in [Figure 7].
|Figure 7: Comparative in vitro drug release profile of effervescent tablets|
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In vivo floating studies
An X-ray image of rabbits was taken on empty stomach prior to administration of tablet formulation, which is shown in [Figure 8]. X-ray images taken at the 2 nd , 6 th and 12 th hour showed the presence of tablets in the stomach region, which indicated its retention in the stomach. The tablets were strong enough for withstanding repetitive gastric contraction. This showed that effervescent floating tablets with improved mechanical strength could prolong gastric retention and results are shown in [Figure 8].
|Figure 8: X-ray images showing gastric retention of the floating matrix tablet formulation G-VI in a rabbit model at different time intervals|
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Pharmacokinetic studies were carried out for F-6 and marketed (Oflox 200 mg tablet) in rabbits. The plasma concentration of drug in Oflox and in the prepared effervescent formulation is shown in [Figure 9]. The T1/2 value for Oflox was found to be 9 h, whereas the T1/2 value for the prepared formulation was found to be 10 h. The Tmax value for both Oflox and the F-6 formulation was found to be 6 h. The Cmax value for Oflox was found to be 20.15 ± 0.612 g/ml, whereas Cmax for F-6 was found to be 18.14 ± 0.356 g/ml as shown in [Figure 9]. The area under the curve values for Oflox and F-6 were 18.37 ± 8.15 and 18.06 ± 7.26 g/h ml, respectively. The mean residence time values for Oflox and F-6 were found to be 14.9 and 17.4 h.
Stability studies were conducted for the final formulation and physico-chemical changes such as color, appearance and drug content were observed. Tablets were analyzed at intervals of 15, 30, 45, 60 and 90 days. Drug content was in the range 92.02 ± 0.02 to 96.12 ± 1.45%. The results indicate that all formulations were stable. Results are shown in [Figure 10].
Mechanism of drug release
From release kinetics it was revealed that the best-fit model for formulation F-6 was Higuchi, with a release exponent value (n) of 0.538, which showed that the mechanism pattern of the tablets was Fickian diffusion.
| Discussion|| |
FT-IR [Figure 1] shows that there is no interaction in the prepared formulations and FT-IR characteristic peaks of the drugs appeared at the same wave number, indicating no modification or interaction between the drug and the polymers used. This showed that there was no potential incompatibility of the drug with the polymers used in the formulations.
The DSC [Figure 2] thermogram of ofloxacin showed the characteristic peak at 271.5°C corresponding to its melting point. The drug peak for the prepared tablet formulation appeared at 269.8°C. This indicates that the drug did not undergo any changes in the formulations.
From the pre-formulation studies it is clear that the tablet has acceptable flow properties and packaging ability, and they are in the range of pharmaceutical limits. Physical evaluation showed that the tablet does not float when hardness is greater than 5 and it is observed that increase in hardness leads the tablet to break in 0.1 N HCl.
In vitro buoyancy studies were identical with in vivo floating studies in rabbits. Hence gastric floating drug delivery was achieved for more than 12 h in all formulations except F-4, F-7, F-9 and F-10.
Swelling studies showed good swelling property and in vitro release of the drug from the floating tablets by the swelling mechanism, which can be clearly observed in the SEM photographs [Figure 3].
When comparing the finalized best formulation F-6 with the marketed product, the study reveals that there is a change in T1/2 value between Oflox and the prepared formulation. Cmax decreased for the prepared formulation F-6 and Tmax for both formulations remained same, suggesting that the bio-availability of ofloxacin is same. In comparison with the marketed formulation, a conventional tablet, the prepared tablet is more advantageous.
This investigation offers an added advantage for drugs, which show better availability in gastric pH and also increased gastric residence time of the dosage form; ofloxacin is a model drug to depict the investigation. While conventional dosage forms fail to maintain gastric residence time, they will undergo rapid disintegration in the stomach. The prepared dosage forms are able to withstand 12 h in the stomach.
| Conclusion|| |
The prepared floating matrix tablets were subjected to various pharmaceutical parameters such as bulk density, tapped density, angle of repose, weight variation, thickness, hardness and friability. The results indicated that the parameters drug content, swelling behavior, in vitro drug release data, in vitro buoyancy and stability data are within pharmacopoeial limits. FT-IR and DSC studies confirmed that there was no interaction between ofloxacin and other ingredients used in the tablet formulations. F-6 showed sustained in vitro drug release, and also showed better swelling and floating lag time. The release kinetics of the drug from the tablets followed the Higuchi model and the mechanism was found to be Fickian diffusion. The stability studies were performed according to ICH guidelines and results confirmed that the selected formulation was stable. In conclusion, we recommend once-daily ofloxacin tablets prepared by combination of Chitosan and Xanthan gum in an effervescent floating matrix for use in treatment of bacterial infections.
| Acknowledgement|| |
The authors wish to thank the principal (JSS College of Pharmacy, JSS University, Mysore) for the support to carry out the research work.
| References|| |
|1.||Shah SH, Patel JK, Patel NV. Stomach specific floating drug delivery system: A review. Int J Pharm Tech Res 2009;1:623-33. |
|2.||Natasha S, Dilip A, Gupta MK, Mahaveer PK. A comprehensive review on floating drug delivery system. Int J Res Pharm Biomed Sci 2011;2:428-41. |
|3.||Mayavanshi AV, Gajjar SS. Floating drug delivery systems to increase gastric retention of drugs: A review. Res J Pharm Tech 2008;1:345-8. |
|4.||Deshpande AA, Shah NH, Rhodes CT. Development of a novel controlled-release system for gastric retention. Pharm Res 1997;14:815-9. |
|5.||Shamim T, Chynthia S. Ofloxacin. Davis's Pocket Clinical Drug Reference. In: Meghan K, Ziegler FA, editors. USA: Davis Company; 2009. p. 195. |
|6.||Pramod P, Someshwara RB, Suresh VK, Basavaraj CS, Anand A. Formulation and in vitro evaluation of floating matrix tablets of ofloxacin. Asian J Res Pharm Sci 2011;1:17-22. |
|7.||Chander SB, Shireesh KR, Nagendra BB. Preparation and evaluation of gastro retentive floating tablets of ketoconazole. Int J Pharm Res Dev 2010;2:174-85. |
|8.||Padmavathy J, Saravanan D, Rajesh D. Formulation and evaluation of ofloxacin floating tablets using HPMC. Int J Pharm Pharm Sci 2011;3:170-3. |
|9.||Musa H, Ochu SN, Bhatia PG. Evaluation of the tablet binding properties of barley (Hordeum vulgare) starch. Int J Appl Pharm 2010;2:4-7. |
|10.||Yvonne SL, Richard P, Fridrun P, Michael NJ. Development of a dual approach to assess powder flow from avalanching behaviour. AAPS Pharm Sci Tech 2000;1:44-52. |
|11.||Sreenivas SA, Gadad AP. Formulations and evaluation of ondansetron HCl directly compressed mouth disintegrating tablets. Indian Drugs 2006;43:35-8. |
|12.||Varshosaz TN, Roozbahani F. Formulation and in vitro characterization of ciprofloxacin floating and bioadhesive extended-release tablets. Drug Deliv 2006;13:277-85. |
|13.||Mina IT. Controlled-release effervescent floating matrix tablets of ciprofloxacin hydrochloride: Development, optimization and in vitro-in vivo evaluation in healthy human volunteers. Eur J Pharm Biopharm 2010;74:332-9. |
|14.||Rosa M, Zia H, Rhodes T. Dosing and testing in-vitro of a bioadhesive and floating drug delivery system for oral application. Int J Pharm 1994;105:65-70. |
|15.||Pramod P, Someshwara RB, Suresh VK, Basavaraj CS, Anand A. Formulation and in vitro evaluation of floating matrix tablets of ofloxacin. Asian J Res Pharm Sci 2011;1:17-22. |
|16.||Somnath S, Sunil C, Bhaswat C. Bio-waiver monograph for immediate release solid oral dosage forms: Ofloxacin. Int J Pharm Pharm Sci 2010;2:156-61. |
|17.||Mahesh C, Paras J, Sachin C, Rajesh S, Pradeep V. Development of sustained release gastro-retentive drug delivery system for ofloxacin: In vitro and in vivo evaluation. Int J Pharm 2005;304:178-84. |
|18.||Hadjiioannou TP, Christian GD, Koupparis MA, Macheras PE. Quantitative calculations in pharmaceutical practice and research. New York: VCH Publishers Inc.; 1993. p. 345-8. |
|19.||Bourne DW. Pharmacokinetics, Modern Pharmaceutics. In: Banker GS, Rhodes CT, editors. 4 th ed. New York: Marcel Dekker Inc.; 2002. p. 67-92. |
|20.||Higuchi T. Mechanism of sustained action medication: Theoretical analysis of rate of release of solid drugs dispersed in solid matrices. J Pharm Sci 1963;52:1145-9. |
|21.||Hixson AW, Crowell JH. Dependence of reaction velocity upon surface and agitation: I - theoretical consideration. Ind Eng Chem 1931;23:923-31. |
|22.||Korsmeyer RW, Gurny R, Doelker E, Buri P, Peppas NA. Mechanisms of solute release from porous hydrophilic polymers. Int J Pharm 1983;15:25-35. |
|23.||Korsmeyer RW, Lustig SR, Peppas NA. Solute and penetrant diffusion in swellable polymers. I. Mathematical modeling. J Polym Sci Polym Phys Ed 1986a;24:395-408. |
|24.||Korsmeyer RW, von Meerwall E, Peppas NA. Solute and penetrant diffusion in swellable polymers. II. Verification of theoretical models. J Polym Sci Polym Phys Ed 1986b;24:409-34. |
[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10]
[Table 1], [Table 2], [Table 3]