Formulation and In Vitro Studies of a Fixed-Dose Combination of a Bilayer Matrix Tablet Containing Metformin HCl as Sustained Release and Glipizide as Immediate Release

The emerging new fixed dose combination of metformin hydrocholride (HCl) as sustained release and glipizide as immediate release were formulated as a bilayer matrix tablet using hydroxy propyl methyl cellulose (HPMC) as the matrix-forming polymer, and the tablets were evaluated via in vitro studies. Three different grades of HPMC (HPMC K 4M, HPMC K 15M, and HPMC K 100M) were used. All tablet formulations yielded quality matrix preparations with satisfactory tableting properties. In vitro release studies were carried out at a phosphate buffer of pH 6.8 with 0.75% sodium lauryl sulphate w/v using the apparatus I (basket) as described in the . The release kinetics of metformin were evaluated using the regression coefficient analysis. There was no significant difference in drug release for different viscosity grade of HPMC with the same concentration. Tablet thus formulated provided sustained release of metformin HCl over a period of 8 hours and glipizide as immediate release.     

In vitro and in vivo evaluation of two extended release preparations of combination metformin and glipizide

A system that can deliver multi-drugs at a prolonged rate is very important to the treatment of various chronic diseases such as diabetes, asthma, and heart disease. Two controlled-release systems, which exhibited similar release profiles of metformin and glipizide, i.e., elementary osmotic pump tablets (EOP) and bilayer hydrophilic matrix tablet (BT), were designed. The effects of pH and hydrodynamic conditions on drug release from two formulations were investigated. It was found that both drug releases from EOP were not sensitive to dissolution media pH and hydrodynamics change, while the release of glipizide from BT was influenced by the stirring rate. Moreover, in vivo evaluation was performed, relative to the equivalent dose of conventional metformin tablet and glipizide tablet, by a three-crossover study in six Beagle dogs. Cumulative percent input in vivo was compared to in vitro release profiles. The linear correlations of metformin and glipizide between fraction absorbed in vivo and fraction dissolved in vitro were established for EOP—a true zero-order release formula, whereas only nonlinear correlations were obtained for BT. In conclusion, drug release from EOP was both independent of in vitro and in vivo conditions, where the best sustained release effect was achieved, whereas the in vitro dissolution test employed for BT needed to be further optimized to be biorelevant.     

Evaluation of hydrophilic,hydrophobic and waxy matrix excipients for sustained release tablets of Venlafaxine hydrochloride

Objective: Venlafaxine is freely soluble In water and administered orally as hydrochloride salt In two to three divided doses. In the present investigation different release retarding matrices have been evaluated for sustained release of venlafaxine hydrochloride (VH) from the formulated tablets.

Materials and methods: Sustained release matrix tablets were formulated using different hydrophilic, hydrophobic and waxy materials as matrix formers. Tableting was done by pre-compression, direct compression and hot melt granulation depending on the type of matrix material used and evaluated for different tests. The formulated tablets were compared with commercial venlafaxine products. In vitro drug dissolution profiles were fitted In different mathematical models to elucidate the release mechanism.

Results: Dissolution data showed that commercial formulations Venlor XR^® and Venfax PR^® released the entire drug withIn 8?h where as the formulated tablets with hydroxypropylmethylcellulose (HPMC) and cetyl alcohol as matrix formers provided sustained release of drug for 14–15?h. The release was found to follow Hixson Crowel and Higuchi kinetics for HPMC and cetyl alcohol tablets, respectively.

Conclusion: The developed matrix tablet formulations with HPMC and cetyl alcohol provided sustained release profiles for prolonged periods than commercial formulations.     

Modulation of drug (metoprolol succinate) release by inclusion of hydrophobic polymer in hydrophilic matrix

The objective of this study was to develop sustained release (SR) matrix tablets of metoprolol succinate (MS), by using different polymer combinations and fillers, to optimize by response surface methodology and to evaluate biopharmaceutical parameters of the optimized product. Matrix tablets of various combinations were prepared with cellulose-based polymers: hydroxy propyl methyl cellulose (HPMC) and ethyl cellulose (EC); and lactose and dibasic calcium phosphate dihydrate (DCP) as fillers. Study of pre-compression and post-compression parameters facilitated the screening of a formulation with best characteristics that underwent here optimization study by response surface methodology (Central Composite Design). The optimized tablet was subjected to further study like scanning electron microscopy, swelling study and in vivo study in rabbit model. Both in vitro and in vivo study revealed that combining of HPMC K100M (21.95%) with EC (8.85%), and use of DCP as filler sustained the action up to 12 h. The in vivo study of new SR tablets showed significant improvement in the oral bioavailability of MS in rabbits after a single oral dose of 25 mg. The delayed T(max) and lower C(max) indicated a slow and SR of MS from the optimized matrix tablets in comparison with the immediate release dosage form. The developed SR (MS) tablet of improved efficacy can perform therapeutically better than conventional tablet.     

Preparation and evaluation of a sustained-release formulation of nifedipine HPMC tablets

A nifedipine (NF) polyethylene glycol (PEG) solid dispersion was prepared. Using this solid dispersion, NF hydroxypropylmethylcellulose (HPMC) matrix tablets were prepared. Both the high-viscosity grade HPMC (Methocel K15M) and low-viscosity grade HPMC (Methocel K100) were applied in the tablets to form the matrix. The dissolution and absorption of NF from the tablet were evaluated as a formulation that had a sustained release over 24 hr. The Hixson-Crowell equation and Higuchi equation were used to investigate the dissolution mechanism, and the erosion and diffusion codependent mechanism was established. Adalat GITS 30 was used as a reference dosage form. Each beagle dog was also administered an intravenous injection to obtain the pharmacokinetics parameters. The Loo-Riegelman method was applied to study the in vitro/in vivo correlation of the tested tablets and Adalat GITS 30, and significant correlation was proved. Absolute bioavailability and comparative bioavailability of the tested tablet were studied. The results indicated that the NF HPMC tablet could be an ideal 24-hr sustained-release formulation.     

Preparation and Evaluation of a Sustained-Release Formulation of Nifedipine HPMC Tablets

A nifedipine (NF) polyethylene glycol (PEG) solid dispersion was prepared. Using this solid dispersion, NF hydroxypropylmethylcellulose (HPMC) matrix tablets were prepared. Both the high-viscosity grade HPMC (Methocel K15M) and low-viscosity grade HPMC (Methocel K100) were applied in the tablets to form the matrix. The dissolution and absorption of NF from the tablet were evaluated as a formulation that had a sustained release over 24 hr. The Hixson-Crowell equation and Higuchi equation were used to investigate the dissolution mechanism, and the erosion and diffusion codependent mechanism was established. Adalat GITS 30 was used as a reference dosage form. Each beagle dog was also administered an intravenous injection to obtain the pharmacokinetics parameters. The Loo-Riegelman method was applied to study the in vitro/in vivo correlation of the tested tablets and Adalat GITS 30, and significant correlation was proved. Absolute bioavailability and comparative bioavailability of the tested tablet were studied. The results indicated that the NF HPMC tablet could be an ideal 24-hr sustained-release formulation.     

In Vitro and In Vivo Evaluation of Two Extended Release Preparations of Combination Metformin and Glipizide

A system that can deliver multi-drugs at a prolonged rate is very important to the treatment of various chronic diseases such as diabetes, asthma, and heart disease. Two controlled-release systems, which exhibited similar release profiles of metformin and glipizide, i.e., elementary osmotic pump tablets (EOP) and bilayer hydrophilic matrix tablet (BT), were designed. The effects of pH and hydrodynamic conditions on drug release from two formulations were investigated. It was found that both drug releases from EOP were not sensitive to dissolution media pH and hydrodynamics change, while the release of glipizide from BT was influenced by the stirring rate. Moreover, in vivo evaluation was performed, relative to the equivalent dose of conventional metformin tablet and glipizide tablet, by a three-crossover study in six Beagle dogs. Cumulative percent input in vivo was compared to in vitro release profiles. The linear correlations of metformin and glipizide between fraction absorbed in vivo and fraction dissolved in vitro were established for EOP—a true zero-order release formula, whereas only nonlinear correlations were obtained for BT. In conclusion, drug release from EOP was both independent of in vitro and in vivo conditions, where the best sustained release effect was achieved, whereas the in vitro dissolution test employed for BT needed to be further optimized to be biorelevant.     

Influence of hydroxypropyl methylcellulose mixture,apparent viscosity,and tablet hardness on drug release using a 2(3) full factorial design

This study investigates the effects of three factors: (1) use of a mixture of two different grades of hydroxypropyl methylcellulose (HPMC), (2) apparent viscosity, and (3) tablet hardness on drug release profiles of extended-release matrix tablets. The lot-to-lot apparent viscosity difference of HPMC K15M on in vitro dissolution was also investigated. Four test formulations were made, each containing 10% of a very water-soluble active pharmaceutical ingredient (API), 32% HPMC K15M, or a mixture of HPMC K100LV and HPMC K100M, 56% diluents, and 2% lubricants. Each formulation was made at two hardness levels. A 2³ full factorial design was used to study various combinations of the three factors using eight experiments conducted in a randomized order. Dissolution studies were performed in USP apparatus I. The values of t_50% (time in which 50% drug is released) and t_lag (lag time, the time taken by the matrix tablet edges to get hydrated and achieve a state of quasi-equilibrium before erosion and the advance of solvent front through the matrix occur) were calculated from each dissolution profile. The similarity factor (f₂) was also calculated for each dissolution profile against the target dissolution profile. A simple Higuchi-type equation was used to analyze the drug release profiles. Statistical analysis using analysis of variance (ANOVA) and similarity factor (f₂) values calculated from the data indicated no significant difference among the t_50% values and dissolution profiles respectively for all formulations. Within the 3.3-6 kp hardness range investigated, dissolution rates were found to be independent of tablet hardness for all the formulations. Although significantly shorter lag times were observed for the tablets formulated with low- and high-viscosity HPMC mixtures in comparison to those containing a single grade of HPMC, this change had no significant impact on the overall dissolution profiles indicated by the similarity factor f₂ values. From this study it can be concluded that lot-to-lot variability in apparent viscosity of HPMC should not be a concern in achieving similar dissolution profiles. Also, results indicated that within the viscosity range studied (12,000-19,500 cps) an HPMC mixture of two viscosity grades can be substituted for another HPMC grade if the apparent viscosity is comparable. Also, the drug release is diffusion-controlled and depends mostly on the viscosity of the gel layer formed.     

Development of sustained release gastro-retentive tablet formulation of nicardipine hydrochloride using quality by design (QbD) approach

The objective of the present study was to develop a sustained release gastro-retentive (SRGR) tablet formulation of nicardipine hydrochloride (HCl) for once-a-day dosing using the quality by design (QbD) approach. The quality target product profile of nicardipine HCl SRGR tablet formulation was defined, and critical quality attributes (CQAs) were identified. Potential risk factors were identified using a fish bone diagram and failure mode effect analysis (FMEA) tool and screened by the Plackett–Burman design, and finally nicardipine HCl SRGR tablet formulation was optimized using the Box–Behnken design. The tablets were prepared by a direct compression technique using polymers such as hydroxypropylmethylcellulose (HPMC K15M), glyceryl behenate, alone or in combinations and other standard excipients. Sodium bicarbonate was incorporated as a gas-generating agent. The effects of polymers and sodium bicarbonate on the drug release profile and floating properties were investigated as these parameters are likely to affect the desired once-a-day dosing regimen and finally the therapeutic efficacy of SRGR drug delivery systems. It was observed that formulation variables X₁: Glyceryl behenate (mg/tab) and X₂: HPMC K15M (mg/tab) strikingly influenced the drug release (%) (Y₁), whereas floating lag time (min) (Y₂) was significantly impacted by the formulation variable X₃: Sodium bicarbonate (mg/tab). A design space plot within which the CQAs remained unchanged was established at a lab scale. In conclusion, this study demonstrated the suitability of a glyceryl behenate-HPMC K15M polymer combination along with sodium bicarbonate to achieve SRGR tablet formulation for once-a-day dosing of nicardipine HCl using the systematic QbD approach.     

Transformation of essential minerals into tablet formulation with enhanced stability

Essential minerals play a very important role in maintaining our physical well-being. In this work, essential minerals; copper sulphate, zinc sulphate, selenium dioxide, chromium picolinate, sodium molybdate and potassium iodide were prepared into tablet formulation with enhanced stability. These minerals are prepared in a coated or as an adsorbate form so as to increase the stability of the minerals. The coated/adsorbate form was formulated into matrix tablets using hydroxypropyl methyl cellulose (HPMC) by the direct compression technique. The distinctively formed tablet was assessed for its physicochemical properties, in-vitro release, microbiological and stability studies. SEM analysis showed that the surface topography of the tablet displayed mechanical interlocking between the trace elements and polymer. During dissolution, the hydrated tablet shows highly porous network of the polymer matrix. Afterwards, they undergo surface erosion from the porous network and the trace minerals gets released. The in-vitro release of zinc sulphate with polymer HPMC K4M showed a sustained release behaviour and fits into the first order and Korsemeyer-Peppas model. The formulation of the trace mineral tablet shows a sustained release profile with increased stability. This trace element matrix tablet supplements is expected to gain acceptance than the marketed products owing to its sustained release behaviour.     

Formulation and release characteristics of hydroxypropyl methylcellulose matrix tablet containing melatonin

A hydroxypropyl methylcellulose (HPMC) matrix tablet containing melatonin (MT) was formulated as a function of HPMC viscosity, drug loading, type and amount of disintegrant, lubricant and glidant, and aqueous polymeric coating level and was compared with two commercial products. The release characteristics of the HPMC matrix tablet were investigated in the gastric fluid for 2 hr followed by study in intestinal fluid. The surface morphology of an uncoated HPMC matrix tablet using scanning electron microscopy (SEM) was crude, showing aggregated particles and rough crystals or pores, but it became smoother as the coating levels increased. As the HPMC polymer viscosity increased, the release rate had a tendency to decrease. As the drug loadings increased, the release rate slightly decreased. When Polyplasdone®XL, Primojel®, and Ac-Di-Sol®, except Avicel®, were incorporated in the HPMC matrix tablet, the release rate was markedly increased. There was no significant difference in release profiles when a mixture of lubricants and glidants (magnesium stearate, talc, and Cab-O-Sil®), except for magnesium stearate alone, was incorporated into low and high viscosity grade HPMC matrix tablets. As the coating level increased, the release rate gradually decreased, giving an increased lag time. The sustained-release HPMC matrix tablet with optimizing formulations may provide an alternative for oral controlled delivery of MT and be helpful in the future treatment of circadian rhythmic disorders.     

Drug-organic electrolyte complexes as controlled release systems

A water-insoluble complex between diltiazem HCl and Na deoxycholate was prepared to achieve sustained release dosage forms. Physicochemical characterization of the drug complex was carried out with differential scanning calorimetry, (1)H-nuclear magnetic resonance, and Fourier transform infrared spectroscopy. These techniques showed that the characteristic peaks in both the drug and the complexing agent (protonated amine and carboxylate) disappeared and new peaks appeared upon formation of the ionic complex. The release of diltiazem from drug-complex tablets was sustained for a long period of time (>24 h) and was dependent on the pH of the dissolution medium. However, the dependence of drug release on pH was eliminated at pH 6-8 and minimized at pH 1.5 when drug-complex powders were incorporated in hydroxypropylmethylcellulose (HPMC) drug carriers. Unlike the release of diltiazem HCl from HPMC drug carriers, drug release from drug-complex/HPMC tablets was linear or near linear irrespective of the viscosity grade of the polymer (E15 to K4M). This is due to a shift in the controlling mechanism of drug release from drug diffusion to erosion of polymer. Also, drug release kinetics was not significantly affected by the water solubility of cationic drugs (diltiazem HCl, verapamil HCl, propranolol HCl, and labetalol HCl) ranging from 1.6 to 62% and the type of amine (i.e., secondary or tertiary). The same release characteristics were observed from the complexes between anionic drugs (Na salicylate, naproxen Na, and tolmetin Na) and benzathine diacetate as found from the complexes between cationic drugs and Na deoxycholate.     

Investigation of the effect of tablet surface area/volume on drug release from hydroxypropylmethylcellulose controlled-release matrix tablets

The purpose of this study was to investigate the influence of tablet surface area/volume (SA/Vol) on drug release from controlled-release matrix tablets containing hydroxypropylmethylcellulose (HPMC). Soluble drugs (promethazine HCl, diphenhydramine HCl, and propranolol HCl) were utilized in this study to give predominantly diffusion-controlled release. Drug release from HPMC matrix tablets with similar values of SA/Vol was comparable within the same tablet shape (i.e., flat-faced round tablets) and among different shapes (i.e., oval, round concave, flat-faced beveled-edge, and flat-faced round tablets). Tablets having the same surface area but different SA/Vol values did not result in similar drug release; tablets with larger SA/Vol values hadfaster release profiles. Utility of SA/Vol to affect drug release was demonstrated by changing drug doses, and altering tablet shape to adjust SA/Vol. When SA/Vol was held constant, similar release profiles were obtained with f2 metric values greater than 70. Thus, surface area/volume is one of the key variables in controlling drug release from HPMC matrix tablets. Proper use of this variable has practical application by formulators who may need to duplicate drug release profiles from tablets of different sizes and different shapes.     

Synchronized and controlled release of metformin hydrochloride/glipizide from elementary osmotic delivery

Abstract

The combination of metformin hydrochloride (MTF) and glipizide (GLZ) is second-line medication for diabetes mellitus type 2 (DMT2). In the present study, elementary osmotic pump ( EOP) tablet is designed to deliver the combination of MTF and GLZ in a sustained and synchronized manner. By analyzing different variables of the formulation, sodium hydrogen carbonate is introduced as pH modifier to improve the release of GLZ, while ethyl cellulose acts as release retardant to reduce the burst release phase of MTF. A two-factor, three-level face-centered central composite design (FCCD) is applied to investigate the impact of different factors on drug release profile. Compared with conventional tablets, the EOP tablet demonstrates a controlled release behavior with relative bioavailability of 99.2% for MTF and 99.3% for GLZ. Data also shows EOP tablet is able to release MTF and GLZ in a synchronized and sustained manner both in vitro and in vivo.     

Influence of Hydroxypropyl Methylcellulose Mixture,Apparent Viscosity,and Tablet Hardness on Drug Release Using a 23 Full Factorial Design

ABSTRACT

This study investigates the effects of three factors: (1) use of a mixture of two different grades of hydroxypropyl methylcellulose (HPMC), (2) apparent viscosity, and (3) tablet hardness on drug release profiles of extended-release matrix tablets. The lot-to-lot apparent viscosity difference of HPMC K15M on in vitro dissolution was also investigated. Four test formulations were made, each containing 10% of a very water-soluble active pharmaceutical ingredient (API), 32% HPMC K15M, or a mixture of HPMC K100LV and HPMC K100M, 56% diluents, and 2% lubricants. Each formulation was made at two hardness levels. A 2³ full factorial design was used to study various combinations of the three factors using eight experiments conducted in a randomized order. Dissolution studies were performed in USP apparatus I. The values of t_50% (time in which 50% drug is released) and t_lag (lag time, the time taken by the matrix tablet edges to get hydrated and achieve a state of quasi-equilibrium before erosion and the advance of solvent front through the matrix occur) were calculated from each dissolution profile. The similarity factor (f₂) was also calculated for each dissolution profile against the target dissolution profile. A simple Higuchi-type equation was used to analyze the drug release profiles. Statistical analysis using analysis of variance (ANOVA) and similarity factor (f₂) values calculated from the data indicated no significant difference among the t_50% values and dissolution profiles respectively for all formulations. Within the 3.3–6 kp hardness range investigated, dissolution rates were found to be independent of tablet hardness for all the formulations. Although significantly shorter lag times were observed for the tablets formulated with low- and high-viscosity HPMC mixtures in comparison to those containing a single grade of HPMC, this change had no significant impact on the overall dissolution profiles indicated by the similarity factor f₂ values. From this study it can be concluded that lot-to-lot variability in apparent viscosity of HPMC should not be a concern in achieving similar dissolution profiles. Also, results indicated that within the viscosity range studied (12,000–19,500 cps) an HPMC mixture of two viscosity grades can be substituted for another HPMC grade if the apparent viscosity is comparable. Also, the drug release is diffusion-controlled and depends mostly on the viscosity of the gel layer formed.     

The influence of HPMC concentration on release of theophylline or hydrocortisone from extended release mini-tablets

Context: Mini-tablets are compact dosage forms, typically 2–3 mm in diameter, which have potential advantages for paediatric drug delivery. Extended release (ER) oral dosage forms are intended to release drugs continuously at rates that are sufficiently controlled to provide periods of prolonged therapeutic action following each administration, and polymers such as hypromelllose (HPMC) are commonly used to produce ER hydrophilic matrices.

Objective: To develop ER mini-tablets of different sizes for paediatric delivery and to study the effects of HPMC concentration, tablet diameter and drug solubility on release rate.

Methods: The solubility of Hydrocortisone and theophylline was determined. Mini-tablets (2 and 3 mm) and tablets (4 and 7 mm) comprising theophylline or hydrocortisone and HPMC (METHOCEL? K15M) at different concentrations (30, 40, 50 and 60%w/w) were formulated. The effect of tablet size, HPMC concentration and drug solubility on release rate and tensile strength was studied.

Results and Discussion: Increasing the HPMC content and tablet diameter resulted in a significant decrease in drug release rate from ER mini-tablets. In addition, tablets and mini-tablets containing theophylline produced faster drug dissolution than those containing hydrocortisone, illustrating the influence of drug solubility on release from ER matrices. The results indicate that different drug release profiles and doses can be obtained by varying the polymer content and mini-tablet diameter, thus allowing dose flexibility to suit paediatric requirements.

Conclusion: This work has demonstrated the feasibility of producing ER mini-tablets to sustain drug release rate, thus allowing dose flexibility for paediatric patients. Drug release rate may be tailored by altering the mini-tablet size or the level of HPMC, without compromising tablet strength.     

Sustained Release Tablet Formulation for a New Iron Chelator

Sustained release tablet formulations for a new orally active iron chelator (1, 2, dimethyl-3-hydroxy-pyrid-4-one, DMHP or L1) have been developed. Coprecipitates containing DMHP and polymer were prepared and compressed into matrix-type tablets. The dissolution profiles as a function of (1) the type of polymer, and (2) polymer content, were determined. Both Eudragit types (RLPM and RSPM) and all hydroxypropylmethylcellulose (HPMC) grades (E4M, E10M, and K4M) exhibited significant sustained release activity. Above a certain ratio, increase in the polymer concentration did not provide any further decrease in the release rates. All grades of HPMC and both Eudragit RSPM and RLPM showed non-Fickian release kinetics. The role of HPMC and Eudragits in the formulation of a sustained release tablet of a water soluble drug is demonstrated.     

Designing of the fixed-dose gastroretentive bilayer tablet for sustained release of metformin and immediate release of atorvastatin

Patients with type 2 diabetes mellitus have a high risk of cardiovascular disease mainly caused by dyslipidemia. Metformin and atorvastatin are preferentially used to treat type 2 diabetes mellitus and dyslipidemia, respectively. The aim of this study was to develop a once-a-day fixed-dose combination tablet containing metformin and atorvastatin. For this purpose, we designed gastroretentive bilayer tablets consisting of 500?mg metformin in a sustained release layer and 10?mg atorvastatin in an immediate release layer. In addition, we modified the formulation to maintain a dual release pattern for the kinetically different layers for once-daily dosing. The gastroretentive bilayer tablet was developed using polyethylene oxide as a swellable polymer and ammonium methacrylate copolymer as a granule-coating polymer with minimal use of excipients. In vitro release patterns of metformin and atorvastatin from the developed formulation were similar to those of the reference drugs, Glucophage XR for metformin and Lipitor for atorvastatin, with satisfactory dissolution similarity factor (f₂) values. The pharmacokinetic study showed the sustained and immediate absorptions of metformin and atorvastatin, respectively, in beagle dogs. The 90% confidence intervals of the ratios of ln values of AUCs of test formulation F3 and respective reference formulations of metformin and atorvastatin were 0.93–1.12 and 0.89–1.17, respectively, compared with their respective reference drugs. This formulation could contribute to improving the compliance and therapeutic outcome of patients with metabolic diseases.     

Sustained Release Tablet Formulation for a New Iron Chelator

Abstract

Sustained release tablet formulations for a new orally active iron chelator (1, 2, dimethyl-3-hydroxy-pyrid-4-one, DMHP or L1) have been developed. Coprecipitates containing DMHP and polymer were prepared and compressed into matrix-type tablets. The dissolution profiles as a function of (1) the type of polymer, and (2) polymer content, were determined. Both Eudragit types (RLPM and RSPM) and all hydroxypropylmethylcellulose (HPMC) grades (E4M, E10M, and K4M) exhibited significant sustained release activity. Above a certain ratio, increase in the polymer concentration did not provide any further decrease in the release rates. All grades of HPMC and both Eudragit RSPM and RLPM showed non-Fickian release kinetics. The role of HPMC and Eudragits in the formulation of a sustained release tablet of a water soluble drug is demonstrated.     

Formulation and Release Characteristics of Hydroxypropyl Methylcellulose Matrix Tablet Containing Melatonin

A hydroxypropyl methylcellulose (HPMC) matrix tablet containing melatonin (MT) was formulated as a function of HPMC viscosity, drug loading, type and amount of disintegrant, lubricant and glidant, and aqueous polymeric coating level and was compared with two commercial products. The release characteristics of the HPMC matrix tablet were investigated in the gastric fluid for 2 hr followed by study in intestinal fluid. The surface morphology of an uncoated HPMC matrix tablet using scanning electron microscopy (SEM) was crude, showing aggregated particles and rough crystals or pores, but it became smoother as the coating levels increased. As the HPMC polymer viscosity increased, the release rate had a tendency to decrease. As the drug loadings increased, the release rate slightly decreased. When Polyplasdone®XL, Primojel®, and Ac-Di-Sol®, except Avicel®, were incorporated in the HPMC matrix tablet, the release rate was markedly increased. There was no significant difference in release profiles when a mixture of lubricants and glidants (magnesium stearate, talc, and Cab-O-Sil®), except for magnesium stearate alone, was incorporated into low and high viscosity grade HPMC matrix tablets. As the coating level increased, the release rate gradually decreased, giving an increased lag time. The sustained-release HPMC matrix tablet with optimizing formulations may provide an alternative for oral controlled delivery of MT and be helpful in the future treatment of circadian rhythmic disorders.