Formulation and Evaluation of sustained release tablets of Ramipril

 

D. Nagasamy Venkatesh1, S. N. Meyyanathan­2, A. Mohamed Sheik Tharik2, Srinivas Rao2

1Department of Pharmaceutics, JSS College of Pharmacy (JSS Academy of Higher Education and Research),

Ooty–643001. The Nilgiris. Tamil Nadu. India.

2Department of Pharmaceutical Analysis, JSS College of Pharmacy

(JSS Academy of Higher Education and Research), Ooty–643 001. Tamil Nadu. India.

*Corresponding Author E-mail: nagasamyvenkatesh@jssuni.edu.in

 

ABSTRACT:

The present study was aimed to formulate and evaluate sustained release tablets for ramipril employing xanthan gum, and to investigate its in vitro and in vivo performance using rabbit as animal model. Sustained release tablets of ramipril were prepared by direct compression technique. The tablets were evaluated for official pharmaco-technical parameters. Bioavailability parameter was undertaken using rabbits to assess the in vivo performance compared with in-house developed conventional formulation. The developed sustained release tablets of ramipril complied with the official tests. The batch prepared using 40 %w/w of xanthan gum exhibited drug release for 24 h in a sustained manner. The drug release from the tablets obeyed non-fickian diffusion and the order of release found to be first order kinetics. The in vivo studies demonstrated that a higher extent of absorption of drug was observed from the sustained release tablet owing to its lower elimination rate and prolonged half-life over developed immediate release tablets. Xanthan gum based matrix formulations exhibited sustained release for a period of 24 h. The sustained release tablets of ramipril were well absorbed and showed a higher extent of absorption over developed IR tablets. Our results suggest that sustained release tablets of ramipril are an efficient drug delivery system, which will over circumvent the problems in conventional therapy.

 

KEYWORDS: Ramipril, Sustained release, Xanthan gum, Bioavailability and Pharmacokinetic evaluation.

 

 

INTRODUCTION:

Ramipril, an antihypertensive agent used in the treatment and management of hypertension1-3. In conventional treatment, ramipril is administered 2-3 times a day due to its shorter half-life. Sustained release (SR) products are fabricated to release the immediate release part to initiate therapeutic concentration by means of a initial dose and then to offer sustained release over the required period of time with the maintenance portion4-5. As the drug has shorter biological half-life and increased need of patient compliance, especially in the management of hypertension suggest the need for oral sustained release formulation of the drug.

 

Therefore, development of such system can lead to reduce the doses to be administered, avoidance of over dose, and it would be a suitable for the treatment and management of hypertension. There are many types of oral sustained release (SR) formulations have been reported to improve the clinical efficacy of drugs with shorter half-lives to improve better patient compliance6. Among the different techniques employed the modulating the drug release through an inert polymeric matrix gained considerable attention. This is due to their excellent flexibility in designing formulation, natural polymer matrix systems are widely used in oral sustained/controlled drug delivery to obtain a desirable drug release profile, cost effectiveness and broad regulatory acceptance7. Employing a suitable rate controlling polymer in the formulation, the matrix can be formulated into tablet by suitable compaction method. Hydration of such polymer results in the formation of gel layer that controls the release rate of the drug. In vitro drug release of water soluble drugs is generally controlled by diffusion out of the gel layer at a rate controlled by the gel viscosity, whereas release for poorly soluble drugs is solely governed by polymer dissolution. Xanthan gum, a natural polymer used in SR dosage forms, offers non-toxic, ability to accommodate high levels of drug loading and non-pH dependence. The rapid formation of a viscous layer upon hydration has been regarded as the essential step in achieving sustained drug release from xanthan gum matrices. Moreover they can be used to control both hydrophilic and hydrophobic drugs, being the release behavior of the drug varies with the nature of the matrix as a consequence of the complex interaction between swelling, diffusion and erosion process8. One of the most important characteristics of xanthan gum is the high swellability, which has a considerable effect on the release kinetics of incorporated drug. Hence, the present study was designed to investigate the in vitro and in vivo performance of sustained release tablets of ramipril and to study the effect of polymer concentration on in vitro and in vivo studies were investigated.

 

MATERIALS AND METHODS:

Materials:

Ramipril and Lisnopril (internal standard) were obtained as a gift samples from Amaranth Pharmaceuticals, Pondichery. Xanthan gum was purchased from S.D Fine chemicals, Mumbai, India. Microcrystalline cellulose was a purchase from Signet Chemical Corporation, Mumbai. Magnesium stearate and Talc were procured from S.D. Fine Chemicals, Mumbai, India. All other chemicals used in the study were of analytical or HPLC grade.

 

METHODS:

Drug – Excipients Interactions:

The drug and excipient compatibility was tested by FT IR spectrometry. FTIR spectra's of the drug alone and drug-excipient physical mixtures (1:1 w/w) were derived from a Shimadzu, Japan

 

Formulation of ramipril immediate release (IR) tablets:

Ramipril immediate release (IR) tablets were formulated using wet granulation technique. Calculated quantities of drug and other excipients with the exclusion of magnesium stearate and talc were mixed in a tumbling mixer for 5 min. The powder mixture was wetted using isopropyl alcohol containing PVP-K-30 served as a granulating fluid so as to form a wet mass. The wet mass was further passed through BSS with an opening aperture of 1.7 mm. The granules were collected and then dried at a temperature of 60°C for 3 h.  The dried granules were passed through BSS 1.0 mm and blended with magnesium stearate and talc (2:1), and compressed with 5 mm concave punches (Rimek, Ahmedabad, India) with a compression force of a 9 KN kept for all the formulations. (Table 1).

 

Formulation of ramipril sustained release (SR) tablets:

A direct compression method was employed for the developing Ramipril sustained release (SR) tablets. Drug and other addictives were mixed in a tumbling mixer for 5 min and subjected for compression using 5 mm concave punches (Rimek, Ahmedabad, India), a compression force of 9 KN was maintained for all the formulations (Table 1).

 

Table 1 Composition of ramipril conventional and sustained release tablets

Formulation code

Ramipril (mg)

Lactose

(mg)

Xanthan gum (mg)

Avicel (mg)

PVP-K-30 (mg)

Magnesium stearate (mg)

Talc (mg)

Total weight (mg)

IR

0.17

91.82

-

-

5

2

1

100

F-1

0.35

-

10

86.65

-

2

1

100

F-2

0.35

-

20

76.65

-

2

1

100

F-3

0.35

-

30

66.65

-

2

1

100

F-4

0.35

-

40

56.65

-

2

1

100

F-5

0.35

-

50

46.65

-

2

1

100

 

Evaluation of granules and tablets:

The prepared granules were characterized for various pharmaco-technical properties as shown in table 2. The developed tablets were examined for pharmaco-technical parameters such as thickness, weight variation test, hardness test, friability test as per official procedures are shown in table 3.

 

Drug content:

Five tablets from the different formulations were weighed and powdered individually. An amount powder from different formulation equivalent to 0.17mg drug for conventional tablets and 0.35mg for SR tablets were extracted with phosphate buffer (pH 7.2) and subjected for sonication. The filtered solution was estimated for the drug content at 208nm using HPLC. The chromatographic system consists of a column C18 (250 mm × 4.6mm, i.d 5µ), mobile phase composed of acetonitrile: potassium dihydrogen ortho phosphate (pH 2.8) (60:40 v/v) a flow rate of 1ml/min. The detection was performed at 208nm. Lisinopril was used as an internal standard. The retention times of ramipril and lisnopril were 10.5 and 5.4min, respectively.

 

In vitro release studies:

The in vitro release studies for the developed IR, SR tablets were performed. The dissolution media consisted of 900mL of phosphate buffer pH at a 7.2 maintained at 37°C±0.5°C stirring speed at 50rpm, using USP XXIII dissolution apparatus (Electrolab, Mumbai, India). 5ml sample was taken out, filtered through a 0.45micro filter and again with another fresh medium maintained under the same conditions. Each test was conducted in triplicate (n=3).

 

Determination of release kinetics:

The different kinetic models were applied to interpret the release rate of the drug from the matrix system. Due to the differences in drug release kinetics, the constant k, the measures of release rate should not be used for comparison9-10. Therefore, to characterize the drug release rates in different experimental conditions, mean dissolution time (MDT) was calculated using the following equation:

 

MDT = n/n+1×k-1/n                                                        (1)

 

Where ‘n’ is the release component and k is the kinetic constant calculated from the above equation.

 

Bioavailability study:

A randomized, two treatment, two period, two sequence, single dose cross over bioavailability study for the developed conventional tablets and (reference product) containing 0.17mg of ramipril and developed sustained release tablets (test product) containing 0.35mg of ramipril was carried out in 6 group of healthy albino rabbits weighing 2.0 to 2.5kg to prove the safety and efficacy of the formulations. The protocol of the study was approved by the institutional animal ethics committee (JSSCP/IAEC/M.PHARM/PHARM. ANALYSIS/03/2013-14 dated 30/08/2013). 0.5ml of blood was withdrawn from the marginal ear vein of rabbits at the predetermined time intervals of 0, 0.5, 1, 1.5, 2, 3, 4, 6, 8, 12 and 24 h using sterilized disposable syringes. The blood sample were collected in a ria vial containing the anticoagulant (100ml of 11% sodium citrate) were centrifuged at 4000rpm for 4 min to separate plasma. The plasma samples were de-protinised using acetonitrile and vortexed for 120 sec. It was further centrifuged at 4000rpm for 4 min and the supernatant liquid was separated and stored in a freezer (-70°C). A reproducible analytical technique was developed for the estimation of the drug in the plasma samples. Non-compartmental pharmacokinetic analysis was then performed. Various pharmacokinetic parameters such as Cmax, Tmax, t˝, Kel, AUCo-t and AUCo-α were estimated using the software PK1 and PK2 solutions.

 

Statistical analysis:

Statistical analysis was performed using SPSS version 13.0. The pharmacokinetic parameters like Cmax, Tmax, t˝, Kel, AUCo-t and AUCo-α of the both the formulations which are presented in mean ± S.D. One way ANOVA (analysis of variance) was applied for the statistical analysis to determined parameters in this study. Statistical significance was defined at p<0.05.

 

RESULTS:

Drug-Excipient Interaction:

Figure.1 and 2 depicts the FTIR spectra's of ramipril, with polymer (xanthan gum 1:1 ratio w/w) and ramipril matrix tablets. The characteristic peaks for ramipril at 1742 (C=O), 3418 (O-H), 1345 (C-N) and 3400-3500 (N-H) were found to appear in subsequent spectra of drug and drug with polymer. The results suggest that there was no evidence of interactions between ramipril and the used excipients.

 

Figure 1: FTIR spectra of ramipril


 

Figure 2: FTIR spectra of ramipril with xanthan gum

 

Physical properties of starting material and granules:

Granulation is the process parameter in production of controlled/sustained release dosage forms.  The granules of different formulations were evaluated for angle of repose, loose bulk density (LBD), tapped bulk density (TBD), Carr’s compressibility index and Hausner’s Factor (HF). The granules indicated good flow ability angle of repose values ranging from 22.15±0.02 to 23.47 ±0.07, according to fixed funnel method. The results of LBD, TBD and compressibility index are mentioned in table 2. The values of bulk density indicated good packing characteristics and Carr’s index (<15) indicating free flowing materials. HF values granules ranged from 1.13 to 1.16 shown in table 2. The Carr's Index was calculated, it was observed that granulation improved both flow ability and compressibility.


 

Table 2: Granular properties of different formulations of ramipril tablets

Formulation

code

Angle of Repose (°)

(n=3 ±SD)

Loose Bulk Density (gm/cm) (n=3±SD)

Tapped Bulk Density (gm/cm3) (n=3±SD)

Carr’s Index (%)

(n=3±SD)

Hausner Ratio

IR

22.15 ± 0.02

0.57± 0.04

0.74± 0.04

6.3± 0.02

1.16

F-1

23.6 ± 0.03

0.33± 0.02

0.40± 0.02

7.3± 0.04

1.14

F-2

23.2 ± 0.06

0.30± 0.05

0.28± 0.05

7.4 ±0.05

1.15

F-3

23.47 ± 0.07

0.30± 0.03

0.33± 0.01

7.8±0.07

1.13

F-4

24.3 ±0.06

0.32 ±0.02

0.33 ±0.02

7.6 ±0.06

1.14

F-5

23.6 ±0.03

0.33 ±0.04

0.38 ±0.01

6.9 ±0.04

1.15

 

Physical properties of tablets:

The physical properties of tablets are presented in Table 3. The thickness of the prepared tablets ranged from 3.30±0.08mm to 3.36±0.06 mm. All the formulations were relatively robust in terms of its pharmaco-technical parameters. Small values in friability imply much less friability during transportation, which is important in terms of sustained release tablets. The friability of the developed IR and SR tablets fell into the range of 0.289±0.018 to 0.453±0.020% respectively. Hardness of the tablets was in the range of 4.00 ± 0.01 to 5.00 ± 0.02 kg/cm2. These results also revealed that the increasing polymer concentration did not alter the hardness and thickness of the tablet significantly. The drug content of the tablets was found to be in the range of 98.44 ± 1.9 to 98.85 ± 0.9 of the labeled amount, and have complied with drug content requirement.

 

Table 3: Tablet properties of different formulations of ramipril tablets

Formulation

code

Weight (mg)

(n=20±SD)

Thickness

(mm) (n=5±SD)

Hardness (kg/cm3) (n=6±SD)

Friability (%)

(n=6±SD)

Drug content (%)

(n=5±SD)

IR

99.6 ±0.40

3.42±0.08

4.0±0.01

0.356±0.046

98.28±1.2

F-1

97.4 ±1.44

3.36±0.06

4.8±0.05

0.289±0.018

98.44±1.7

F-2

98.8 ±1.81

3.30±0.08

5.0±0.02

0.290±0.018

98.44±1.9

F-3

98.9 ±1.82

3.33±0.04

4.5±0.04

 0.453±0.020

98.85±0.9

F-4

99.2 ±1.74

3.36 ±0.05

4.6 ±0.03

0.392 ±0.310

97.3 ±1.2

F-5

99.1 ±1.65

3.45 ±0.02

4.5 ±0.05

0.425 ±0.110

98.1 ±1.5

 

In vitro release studies:

The tablets were maintained during the study and a hydrated gel layer was formed. Therefore, diffusion was taken as the most significant factor in controlling the rate of drug release from the system. Figure 3 shows the in vitro release profile of ramipril from the developed conventional and developed sustained release tablets. An inverse relationship was noted between the amount of polymer and release rate of drug. The drug release rate from xanthan gum based matrix tablets indicates the drug release was decreased with an increase in the polymer concentration.

 

Release kinetics:

In order to describe the kinetics of release process of drug in the formulations, various equations were used, such as zero order rate equation, which describes the system where the release rate is independent of the concentration of the dissolved species i.e. percent dissolved as a function of time.  The plots are curvilinear suggesting that the process is not zero order in nature. This indicates that the dissolution rate of the drug is independent of the amount of drug available for dissolution and diffusion from the matrix. The dissolution data of all formulation at pH 7.2 were plotted in accordance with the first order equation, i.e. the logarithm of percent remained as a function of time. It is evident from the table 4, that the release of drug from the optimized batch selected based on the in vitro release profile followed first order kinetics obeying non-fickian diffusion as their main mechanism. Mean dissolution time (MDT) is used to characterize the drug release rate from the dosage form and retarding efficiency of the polymer. A higher MDT indicates a higher drug retarding ability of the polymer and vice versa.


 

Fig. 3. In vitro release profile of ramipril from developed IR ramipril formulation (♦) and developed SR ramipril formulations (F-1-■), (F-2-▲) and (F-3-×) (F-4-×) (F-5-×)

 

Table 4: Regression coefficient (r2) of ramipril from data from studied matrices according to different kinetic models, diffusion exponent (n) of peppa’s model and mean dissolution time (MDT)

Formulation code

Zero order

(r2)

First order

(r2)

Higuchi

(r2)

Peppa’s

MDT

(h)

n

(r2)

F-4

0.839

0.938

0.960

0.497

0.958

0.403

 

Bioavailability study:

The relative bioavailability of the developed ramipril sustained release (SR) tablet 1.5mg (F-3), selected based on the in vitro dissolution data was compared with developed ramipril IR tablet 0.17mg. The developed sustained release (SR) tablet produced a plasma concentration time profile typical of the prolonged dissolution characteristic of a SR formulation as evident from table 5. The plasma concentration-time profiles of ramipril explicitly indicated xanthan gum successfully sustained the absorption of ramipril. This was indicated by lower variation in plasma concentrations, which indicates longer time to peak (Tmax) and lower plasma concentration (Cmax). There was a significant difference in the absorption as assessed by measurements of AUCo-t. However, AUCo-t value for the developed SR tablets was 1.75 times higher than the developed IR tablets indicating more efficient and sustained drug delivery, which would maintain plasma ramipril levels well. The difference of AUCo-t due to the difference in administered dose. This shows that AUCo-t may direct proportional with the dose administered. This was also evident by the lower elimination rate (1.36 times lesser for developed SR tablets) and higher t˝ values (1.35 times more than developed IR tablets). The prolonged t˝ is another important indication on the in vivo performance of the sustained release tablets in providing prolonged drug delivery. The pharmacokinetic parameters of the two different formulations of ramipril were compared statistically by one way ANOVA (analysis of variance) using SPSS version 13.0. The pharmacokinetic parameters such as Cmax, Tmax, t˝, Kel, AUCo-t and AUCo-α of the developed immediate release and sustained release formulations of ramipril were found to be significantly different (p<0.05) by one way ANOVA.

 

Table 5: Mean pharmacokinetic profile of developed IR and SR ramipril tablets

Pharmacokinetic Parameters

Developed ramipril IR tablets

Developed ramipril SR tablets

Cmax (ng/ml)

28.5±0.707

35.5±0.70

Tmax (h)

2±0.01

3 ±0.01

AUCo-t (ng/ml)

120.75 ±4.42

241 ±4.59

t1/2 (h)

2.62 ±0.474

3.53 ±0.32

Kel  (h-1)

0.268±0.04

0.197±0.017

AUC0-α (ng/ml)

159.03 ±16.44

279 ±11.64

 

DISCUSSION:

The aim of this study was to prepare ramipril sustained release tablets and to evaluate its in vitro and in vivo potential. It was observed that there was no interaction between the drug and excipients used in the study. Powder is the key process involved in the formulation of tablets. The powder was found to exhibit good flow properties. It also significantly improved the flow ability and compressibility of powder. The concentration of polymer level does not affect the physical properties of the powder significantly. Also, it was observed that the polymer level does not influence derived properties of powder and tablets. Xanthan gum did not have any significant effect on the binding properties of tablets as indicated by its thickness and friability. The drug release from these tablets decrease with an increase in polymer concentration, which is due to the formation of gel in the diffusion layer and mechanical properties of polymer. The MDT is another parameter that reveals the drug retarding efficacy of the polymer. There was a linear relationship observed with xanthan gum polymer loading and mean dissolution value, which is irrespective of drug and type of polymer. The relative bioavailability of developed SR tablets demonstrated a longer time to reach a peak concentration than the developed IR tablets and appeared to be more consistent in overall performance. This fact was supported by lower variation in plasma concentration, longer time to peak data’s.  The developed sustained release tablets of ramipril were well absorbed and the extent of absorption was higher than that of developed IR tablets. The sustained release drug delivery system developed in the present study will overcome the drawbacks associated with the conventional therapy. However, bioavailability studies employing human volunteers are needed to carry out to establish its potential effect.

 

CONCLUSION:

The present study was carried out to develop oral sustained release systems for ramipril using xanthan gum as swellable controlled systems as formulation strategies. The natural xanthan gum-based matrix formulations exhibited sustained release behavior over a 24 h period.   The developed sustained release tablets of ramipril were well absorbed and the extent of absorption was higher than that of the developed IR tablets. The better plasma level will overcome the draw backs associated with the conventional therapy. However, bioavailability studies employing human volunteers needed to be carried out to establish its potential effect.

 

Acknowledgement:

The authors would like to thank the Department of Science and Technology – Fund for Improvement of Science and Technology Infrastructure in Universities and Higher Educational Institutions (DST-FIST), New Delhi for their infrastructure support to our department.

 

CONFLICT OF INTEREST:

No conflict of interest in the present study.

 

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Received on 01.10.2019           Modified on 26.11.2019

Accepted on 21.01.2020         © RJPT All right reserved

Research J. Pharm. and Tech. 2020; 13(8):3873-3878.

DOI: 10.5958/0974-360X.2020.00685.X