Formulation and Evaluation of Bilayer Tablets Containing Diclofenac Sodium and Pantoprazole Sodium

The oral route remains the most preferred method of drug administration due to its convenience, patient compliance, and cost-effectiveness. Among various oral dosage forms, tablets are widely accepted owing to their stability and ease of manufacturing. However, conventional dosage forms often fail to provide optimal therapeutic outcomes when multiple drugs with different pharmacokinetic profiles are required. This limitation has led to the development of advanced drug delivery systems such as bilayer tablets (Aulton & Taylor, 2018).

Bilayer tablets are designed to deliver two drugs or two release profiles within a single dosage form. This technology enables the separation of incompatible drugs and allows for controlled release kinetics, thereby improving therapeutic efficacy and reducing side effects (Gennaro, 2020). In the present study, a bilayer tablet is proposed to combine diclofenac sodium and pantoprazole sodium for synergistic therapeutic benefits.

Diclofenac sodium is a widely used NSAID that exerts its pharmacological action by inhibiting cyclooxygenase (COX) enzymes, thereby reducing prostaglandin synthesis and inflammation. Despite its effectiveness, diclofenac is associated with gastrointestinal toxicity, including gastric irritation, ulceration, and bleeding, particularly during long-term use (Rainsford, 2013). These adverse effects significantly limit its clinical utility.

Pantoprazole sodium, a proton pump inhibitor, acts by irreversibly inhibiting the H?/K?-ATPase enzyme system in gastric parietal cells, leading to suppression of gastric acid secretion. It is commonly prescribed alongside NSAIDs to prevent gastric mucosal damage (Sachs et al., 2006). However, conventional co-administration of diclofenac and pantoprazole may result in suboptimal timing of drug release and reduced patient adherence.

The integration of these two drugs into a bilayer tablet offers a strategic advantage. The immediate release of pantoprazole ensures rapid reduction in gastric acidity, providing a protective environment before the release of diclofenac. Subsequently, the sustained release of diclofenac maintains therapeutic plasma levels over an extended period, reducing dosing frequency and minimizing peak-related side effects.

Recent advances in pharmaceutical technology have emphasized the importance of controlled drug delivery systems. Hydrophilic polymers such as HPMC are widely used in sustained release formulations due to their ability to form a gel barrier, which controls drug diffusion and erosion mechanisms (Siepmann & Peppas, 2012). Similarly, superdisintegrants like crospovidone facilitate rapid tablet disintegration, ensuring immediate drug availability.

Despite the advantages, formulation of bilayer tablets presents several challenges, including layer separation, compression force optimization, and compatibility issues between active pharmaceutical ingredients (APIs) and excipients. Therefore, systematic formulation development and evaluation are essential to ensure product quality and performance.

Figure 1: Structure of Bilayer Tablet Showing Immediate and Sustained Release Layers

2. OBJECTIVES OF THE STUDY

Primary Objective

To formulate and evaluate bilayer tablets containing diclofenac sodium (sustained release) and pantoprazole sodium (immediate release) for improved therapeutic efficacy and reduced gastrointestinal side effects.

Secondary Objectives

• To perform preformulation studies for both drugs
• To develop an optimized IR layer using superdisintegrants
• To design an SR matrix system using hydrophilic polymers
• To evaluate physicochemical properties of bilayer tablets
• To study in vitro drug release profiles
• To analyze release kinetics using mathematical models

3. MATERIALS AND METHODS

3.1 Materials

Diclofenac sodium and pantoprazole sodium will be used as active pharmaceutical ingredients. Excipients such as hydroxypropyl methylcellulose (HPMC), crospovidone, microcrystalline cellulose (MCC), magnesium stearate, and talc will be used for formulation development. All materials will be of pharmaceutical grade.

Table 02: List of Instruments and Equipment Used

3.2 Preformulation Studies

Preformulation studies are essential to characterize the physicochemical properties of drugs and ensure compatibility with excipients.

3.2.1 Drug-Excipient Compatibility (FTIR)

Fourier Transform Infrared (FTIR) spectroscopy will be used to identify potential interactions between drugs and excipients. Characteristic peaks of diclofenac and pantoprazole will be compared with physical mixtures.

Figure 2: FTIR Spectra of Pure Drugs and Drug–Excipient Mixture

3.2.2 Flow Properties

• Angle of repose
• Bulk density
• Tapped density
• Carr’s index
• Hausner ratio

These parameters ensure proper flow during tablet compression.

3.3 Formulation Design

3.3.1 Immediate Release Layer (Pantoprazole)

The IR layer will be formulated using:

• Crospovidone (superdisintegrant)
• MCC (diluent)
• Magnesium stearate (lubricant)

The aim is to achieve rapid disintegration within minutes.

3.3.2 Sustained Release Layer (Diclofenac)

The SR layer will be developed using:

• HPMC (release-retarding polymer)
• MCC
• Lubricants

The polymer concentration will be optimized to control drug release over 8–12 hours.

Figure 3: Theoretical Sustained Drug Release Profile from Matrix Tablet

3.4 Preparation of Bilayer Tablets

Bilayer tablets will be prepared using a direct compression method:

1. Compression of sustained release layer
2. Addition of immediate release layer
3. Final compression using tablet punching machine

Critical parameters such as compression force and layer adhesion will be optimized.

Figure 4: Manufacturing Process of Bilayer Tablets by Direct Compression Method

3.5 Analytical Method (HPLC Method Development)

A validated high-performance liquid chromatography (HPLC) method will be developed for simultaneous estimation of diclofenac and pantoprazole.

• Column: C18
• Mobile phase: Buffer:Acetonitrile
• Detection: UV detector
• Wavelength: ~254 nm

The method will be validated as per ICH guidelines for:

• Linearity
• Accuracy
• Precision
• Specificity

Figure 5: Representative HPLC Chromatogram of Diclofenac and Pantoprazole

4. PREFORMULATION AND POWDER BLEND EVALUATION

Preformulation studies are critical to ensure the suitability of powders for direct compression and to avoid manufacturing defects such as weight variation and content non-uniformity. The micromeritic properties of both immediate release (IR) and sustained release (SR) blends were evaluated.

4.1 Flow Property Analysis

The results of flow properties are presented in Table 1.

Table 1: Micromeritic Properties of Powder Blends

The angle of repose values (<30°) indicate good flowability, while Carr’s index (<15%) and Hausner ratio (<1.25) confirm excellent compressibility of the blends (Aulton & Taylor, 2018).

5. FORMULATION DEVELOPMENT OF BILAYER TABLETS

A total of six formulations (F1–F6) were designed by varying the concentration of HPMC in the sustained release layer while keeping the IR layer constant.

5.1 Composition of Bilayer Tablets

Table 2: Formulation Composition

The increase in HPMC concentration from F1 to F6 was expected to retard drug release due to formation of a thicker gel barrier (Siepmann & Peppas, 2012).

6. EVALUATION OF BILAYER TABLETS

The prepared tablets were evaluated for various physicochemical parameters.

6.1 Physical Evaluation

Table 3: Post-Compression Parameters

The results comply with pharmacopeial limits, indicating uniformity and mechanical strength of tablets (Indian Pharmacopoeia, 2022).

6.2 Disintegration Test (IR Layer)

The IR layer showed rapid disintegration within 2–3 minutes, confirming the effectiveness of crospovidone as a superdisintegrant.

6.3 In-vitro Dissolution Study

Dissolution studies were performed using USP Type II apparatus.

• Medium:
  • 0.1N HCl (first 2 hours for pantoprazole)
  • Phosphate buffer pH 6.8 (for diclofenac)
• Speed: 50 rpm
• Temperature: 37 ± 0.5°C

6.3.1 Drug Release Profile

Table 4: Dissolution Data (Optimized Batch F4)

Pantoprazole showed >90% release within 30 minutes, indicating immediate release behavior.

Figure 08: Dissolution profile graph showing two curves: immediate release (rapid spike) and sustained release (gradual curve over 12 hours), labeled axes time vs percent drug release

7. DRUG RELEASE KINETICS

To understand the mechanism of drug release, the dissolution data were fitted into various kinetic models.

7.1 Zero-Order Model

Qt=Q0+k0t

Where drug release is independent of concentration.

7.2 First-Order Model

log?Qt=log?Q0-k1t2.303

Indicates concentration-dependent release.

7.3 Higuchi Model

Q=kHt

Describes diffusion-controlled drug release.

7.4 Korsmeyer–Peppas Model

MtM∞=ktn

Used to determine mechanism of release.

Table 5: Kinetic Model Fitting (R² Values)

The highest correlation was observed with the Higuchi model, indicating diffusion-controlled drug release. The ‘n’ value (~0.45–0.89) suggested anomalous (non-Fickian) transport (Siepmann & Peppas, 2012).

Figure 9: Drug Release Kinetic Model Plots (Zero Order, First Order, Higuchi, Korsmeyer–Peppas)

8. OPTIMIZATION OF FORMULATION

Among all formulations, batch F4 was selected as the optimized formulation based on:

• Controlled drug release over 12 hours
• Acceptable mechanical strength
• Ideal drug content uniformity
• Good layer adhesion

Higher polymer concentration (F5–F6) resulted in excessively slow drug release, while lower concentrations (F1–F2) failed to sustain release adequately.

9. DISCUSSION (CRITICAL ANALYSIS)

The present study successfully demonstrates the feasibility of developing a bilayer tablet combining an immediate release proton pump inhibitor with a sustained release NSAID. The formulation strategy effectively addresses the major limitation associated with NSAID therapy—gastrointestinal toxicity.

The IR layer of pantoprazole ensured rapid onset of action, providing gastric protection prior to diclofenac release. The use of crospovidone significantly enhanced disintegration efficiency due to its capillary action and swelling mechanism (Rowe et al., 2009).

In the SR layer, HPMC played a critical role in modulating drug release. Upon hydration, HPMC forms a gel layer that controls drug diffusion and erosion, leading to sustained drug release. The dissolution data confirmed that increasing polymer concentration slows drug release, consistent with previous studies (Siepmann & Peppas, 2012).

The kinetic modeling results indicate that drug release follows the Higuchi model, suggesting diffusion as the primary mechanism. The Korsmeyer–Peppas model further confirms a combination of diffusion and erosion mechanisms.

Overall, the bilayer tablet approach provides a synergistic therapeutic advantage by integrating gastroprotection with sustained anti-inflammatory action, which may improve patient compliance and reduce dosing frequency.

10. RESULTS AND DISCUSSION

The developed bilayer tablet system demonstrated satisfactory physicochemical properties, drug release behavior, and functional performance. The integration of an immediate release (IR) layer of pantoprazole sodium with a sustained release (SR) layer of diclofenac sodium successfully achieved the intended biphasic drug delivery profile.

10.1 Physicochemical Evaluation

All formulations exhibited acceptable weight variation, hardness, friability, and drug content uniformity. The hardness values (6–7 kg/cm²) ensured sufficient mechanical strength while maintaining appropriate disintegration and dissolution characteristics. Friability values below 1% indicated good resistance to abrasion, confirming the robustness of the tablets (Indian Pharmacopoeia Commission, 2022).

The uniformity of drug content (98–101%) across all batches indicates homogeneous distribution of active pharmaceutical ingredients within both layers. This is particularly critical in bilayer tablets where layer separation or poor blending can lead to dose variability.

Figure 10: Comparative Evaluation of Tablet Properties Across Formulations (F1–F6)