INTRODUCTION:

Oral drug administration has been the most favourable and convenient route for drug delivery. GRDDS is the novel drug delivery system which prolongs gastric retention time. GRDDS has recently been of increasing interest to achieve improved therapeutic advantages such as ease of administration, patient compliance by reducing dosing frequency and flexibility in formulation¹. The term "in-situ gel" describes a polymer solution that can be supplied as a liquid and that, when exposed to physiological conditions such as temperature changes, pH changes, ionic changes, ultraviolet-induced gelation and solvent exchange-induced gelation, goes through a phase transition to semisolid gel.

The capacity of in-situ gel forming technologies to produce regulated and prolonged drug administration has been extensively researched. These systems offer enhanced patient compliance, bioavailability, and ease of administration.^2-5 The gel created by the in situ gelling system is lighter than gastric fluids, it either floats over the contents of the stomach or sticks to the gastric mucosa because of bio adhesive nature of polymer and produce gastric retention of dosage form and increase gastric residence time resulting in prolonged drug delivery in gastrointestinal tract^5,6.

Captopril has been extensively utilised in the treatment of congestive heart failure and hypertension^7-10. The medication has a 2-3h elimination half-life following an oral dosage and is easily soluble in water. At pH 1.2, the medication is stable and as pH rises, it becomes unstable. Nevertheless, the antihypertensive effect of a single oral dosage lasts for just 6–8 hours. Therefore, a daily dose of 37.5–75mg must be taken three times a day for therapeutic use^11-13. The current study's goal was to create a gastroretentive in situ gel of captopril using a mixture of gellan gum and HPMC K4M to extend gastric retention. The gel was assessed using metrics such as floating lag time, floating time, density, pH, in vitro drug release, drug content and in vitro gelling capacity.

MATERIALS:

Captopril was obtained as a gift sample from Nucleus Formulation Pvt. Ltd, Chhatral, Gandhinagar. Gellan gum and HPMC K4M were procured from Yarrow chem Product, Mumbai. Calcium carbonate was procured from ACS chemicals, Ahmedabad. Trisodium citrate was procured from Krishna chemicals, Ahmedabad.

METHODS:

Preparation of in situ gelling solution:

Gellan gum was added to 50 millilitres of deionized water containing sodium citrate and stirred continuously until the gum was completely dissolved. The prepared solution was stirred while heated to 90˚C. The suitable amount of CaCO₃ was added to provide a uniform dispersion after cooling below 40˚C. The resulting solution was then used to dissolve captopril and HPMC K4M. Final volume was made up to 100ml with deionized water^14-16.

Experimental design:

A 3² full factorial design with 9 runs (F1–F9) was applied. Gellan gum concentration (X₁) and HPMC K4M concentration (X₂), two independent variables, were chosen at three different values. Y₁ percentage of drug release at 6 h, Y₂ viscosity and Y₃ floating lag time were the dependent variables. Design Expert Software was used to analyse the experimental data and calculate the main effects and interaction terms.^14-17. (Table-1 and 2).

Table 1: Variable in 3²factorial design

Independent variables

level

-1

X_1: Gellan gum

X₂:HPMC K4M

0.25

0.5

0.6

0.75

0.7

Dependent variables: Y₁: % In vitro drug release at 6 h, Y₂: viscosity (cps) and Y₃: floating lag time (sec)

Evaluation of Gastroretentive In situ Gel:

Drug – excipient interaction study by FTIR:

The Fourier transform infrared spectrum of the moisture-free powder API sample and the physical mixture was recorded with an FTIR spectrophotometer using the potassium bromide (KBr) pellet. The characteristic peaks of different functional groups were compared with the reported standard peak¹⁸.

pH measurement:

A 50ml beaker was used to determine the pH, and a digital pH meter was used to measure the pH at room temperature.^15,17.

In vitro floating study:

The floating study was carried out with 500ml of 0.1 N HCl (pH 1.2) in a beaker. A precisely measured 10ml of solution was added to 0.1 N HCl. The floating lag time and the total floating time were measured^17,19.

In vitro gelling capacity:

The gelling capacity was determined by a visual method. The gelling capacity was measured by placing 15 ml of gelation solution (0.1 N hydrochloric acid ) in a test tube and maintaining it at 37±1˚C. 1ml of solution was added with a pipette to the solution. When the solution came into contact with the gelation solution, it immediately transformed into a stiff gel. The gelling capacity was evaluated on the basis of stiffness of formed gel and time period for which formed gel remained as such. The gelling capacity was classified in 3 categories such as (1) + = forms gel after few minutes, remains for less than 5hours. (2) + + = immediate gelation remains for less than 12hours. (3) +++ = immediate gelation remains for 12hours and more^3,18,20.

Viscosity measurement of in situ gel:

A 100ml of the sample was used to determine the viscosity of the in-situ gelling solution with a Brookfield viscometer. Measurements were made using a spindle no 21 at 60rpm. The viscosity was determined at 37 ˚C²¹.

Determination of drug content:

The amount of drug in the formulation was determined by dispensing 10ml of in situ gel (equivalent to 50 mg of captopril) into a 100ml volumetric flask. The final volume was make up to 100ml 0.1 N HCl. After 15 minutes of sonication, the solution was filtered by filter paper. The absorbance was then taken at 212 nm using 0.1 N HCl, pH 1.2 as a blank^17,22.

Table 2: Composition of factorial batches

Ingredients (%w/v)	F1	F2	F3	F4	F5	F6	F7	F8	F9
Captopril	0.5	0.5	0.5	0.5	0.5	0.5	0.5	0.5	0.5
Gellan Gum	0.25	0.25	0.25	0.5	0.5	0.5	0.75	0.75	0.75
HPMC K4M	0.5	0.6	0.7	0.5	0.6	0.7	0.5	0.6	0.7
CaCO₃	0.5	0.5	0.5	0.5	0.5	0.5	0.5	0.5	0.5
Sodium Citrate	0.2	0.2	0.2	0.2	0.2	0.2	0.2	0.2	0.2
Water (ml) q.s.	100	100	100	100	100	100	100	100	100

In vitro drug release:

The drug release study was carried out using USP Type II paddle type apparatus at 37°C±0.5°C and at 50rpm using 900 ml of a dissolution medium having 0.1N HCl (pH 1.2). At the predetermined time intervals, 10 ml samples were withdrawn and replaced with the same volume of fresh dissolution medium. The sample was filtered through a 0.45m membrane filter, diluted, and then suitably analyzed using a UV spectrophotometer at 212nm.^22,23.

In vitro drug release kinetic:

The drug release data here was analyzed using the Korsmeyer-Peppas, zero order, first order, and Higuchi model. To understand the drug release mechanism, dissolution data was analyzed using Korsmeyer-Peppas equation, where the n value determines the drug release mechanism,^15,23.

Stability study:

The optimized formulation was studied for a 1 month in a stability chamber at 40⁰C and 75% RH. The optimized formulation was analyzed for percentage drug release, viscosity, floating lag time and pH.^3,18.

RESULT:

Drug-excipient compatibility study by FTIR

Figure 1: IR spectra of captopril

Figure 2: IR spectra of physical mixture (Captopril + Gellan gum +HPMC K4M)

The presence of peak at 2978.09 cm^-1 (O-H stretching), 2937 cm^-1 (C=O stretching), 2565.33 cm^-1 (S-H stretching), and 1247.94 cm^-1 (C-N stretching) in the IR spectra of the physical mixture of drug and polymer are among the characteristic IR bands of captopril. These bands remained intact. So, from the IR analysis it was concluded that there is no interaction between drug and polymers.

pH, drug content and In vitro floating study:

The in-situ gel's pH was within the permissible range of 7-8. It was shown that the percentage of drug content ranged from 97.25% to 99.28% (Table 3). The floating Lag time and floating time are shown in Table 3.

In vitro gelling capacity and viscosity:

In vitro gelling capacity of all formulations is given in Table 3. All of the formulations were found to exhibit instant gelation within 10sec and the gel structure remained intact for over 12h. All of the formulations' average viscosities were found to be between 45 and 400 cps.

Table 3: Evaluation parameter for floating in situ gel (n=3)

Batch code	pH	In vitro gelling capacity	Gelation time (sec)	Floating lag time (sec)	Floating time (h)	Viscosity (cps)	Drug content (%)
F1	7.18±0.1	+++	6	11±1.0	8	45	98.23±0.5
F2	7.20±0.1	+++	4	20±1.8	9	67	98.75±0.9
F3	7.16±0.2	+++	3	22±0.2	10	105	97.25±0.7
F4	7.28±0.4	+++	7	19±1.3	11	134	98.13±0.2
F5	7.31±0.3	+++	6	24±0.9	12	165	97.86±0.9
F6	7.35±0.2	+++	2	31±1.7	>12	198	98.45±0.8
F7	7.37±0.2	+++	5	29±1.0	>12	257	98.11±0.7
F8	7.40±0.4	+++	7	32±0.5	>12	305	99.12±0.4
F9	7.36±0.2	+++	6	36±0.1	>12	400	99.28±0.8

Values are expressed as mean±SD (n=3)

In vitro drug release:

Figure 3: Drug release profile for formulation F1-F9

It was observed that formulations F3, F6 and F9 show drug release of up to77.77±1.76 %, 64.53± 2.57 % and 47.72±1.86 % respectively at 6 h (Table 4). The batch F5 was shown drug release 100.46±1.18 at 12 h.

In vitro drug release kinetic:

It was concluded that Higuchi model was the best fit for majority of the formulation according to value of regression coefficient (R²).The n value indicates the drug release mechanism, which is in the range of 0.3842- 0.7140. The in vitro release kinetic data is shown in Table 4.

Table 4: Release kinetic data of in situ gel

Batch code	R²				n value
Batch code	Zero	First	Higuchi	Korsmeyer Peppas	n value
F1	0.9878	0.9569	0.9953	0.9894	0.3842
F2	0.9882	0.9453	0.9968	0.9967	0.4236
F3	0.9839	0.9276	0.9982	0.9965	0.4642
F4	0.9878	0.9260	0.9969	0.9970	0.4876
F5	0.9880	0.9237	0.9959	0.9957	0.4925
F6	0.9645	0.8615	0.9943	0.9942	0.5627
F7	0.9644	0.8477	0.9966	0.8479	0.6136
F8	0.9780	0.8576	0.9995	0.9956	0.6634
F9	0.9915	0.8985	0.9939	0.9987	0.7140

DISCUSSION:

In vitro floating study:

A crosslinked three-dimensional gel network is created when the formulation reacts with the acidic medium through the reaction of calcium ions and gellan gum. Additionally, carbon dioxide is emitted and becomes retained in the gel network, causing the system to be buoyant for longer than 12 hours²⁵. It was found that when polymer concentration rises, floating lag time also rises. The floating lag time was greater in the batches [F3, F6, and F9] due to high concentration of HPMC K4M. The batches [F1, F4 and F7] exhibited lower floating lag time.

In vitro gelling capacity:

For a considerable amount of time, the in-situ gel should not dissolve or erode. Because the drug molecules must pass through the intricate three-dimensional structure of polymer chains in order to reach the physiological milieu, the gel's stiffness is allows for the medication's prolonged administration.^{17, 26}

Viscosity:

The viscosity of the formulation increases with an increase in gellan gum and HPMC K4M content. The reason for the increase in viscosity was that a higher gellan gum content increased the viability of the calcium cation binding sites. Moreover, the presence of HPMC K4M contributes to the system's increased viscosity.

In vitro drug release:

It was observed that as the concentration of polymer increases rate and extent of drug release decreases which is due to increase in the viscosity of the polymer matrix and also increase in the diffusion path length which the drug molecules have to transverse. Burst effect was observed during initial phase of drug release which further showed moderate release as time proceeds^16,17.

In vitro drug release kinetic:

The best linearity was found in Higuchi model equation The F1-F5 signified that the transport of the drug is by fickian mechanism, while F6-F9 follows non-fickian anomalous transport.

Statistical analysis:

Analysis of factorial batches data was done using Design Expert DoE Software 6.0 version

Table 5: Regression analysis

Dependent variable	Sources	Sum of Squares	DF	Mean Square	F-value	P-value
Y₁ *(In vitro* drug release at 6 h )**	Model (Linear)	1401.78	2	700.89	466.72	< 0.0001
	X₁	1235.25	1	1235.25	822.56	< 0.0001
	X₂	166.53	1	166.53	110.89	< 0.0001
Y₂ (Viscosity)	Model (Quadratic)	1.066E+005	5	21317.19	180.28	< 0.0001
	X₁	87604.17	1	87604.17	740.86	< 0.0001
	X₂	13728.17	1	13728.17	116.10	< 0.0001
	X₁²	1825.19	1	1825.19	15.44	0.0057
	X₂²	89.95	1	89.95	0.76	0.4120
	X₁X₂	2652.25	1	2652.25	22.43	0.0021
Y₃ (Floating lag time)	Model(Linear)	472.67	2	236.33	128.37	< 0.0001
	X₁	322.67	1	322.67	175.26	< 0.0001
	X₂	150.00	1	150.00	81.48	< 0.0001

In vitro drug release at 6 h Y₁ = 65.95 – 14.35*X₁- 5.27 *X₂

X₁ and X₂had a negative effect on % cumulative drug relase.So it was concluded that % drug release decreased with an increase the concentration of gellan gum and HPMC K4M.

Viscosity:

Y₂ = 163.66 + 120.83*X₁+ 47.83*X₂+ 25.71*X₁²+ 5.71*X₂²+ 25.75 *X₁*X₂

Gellan gum and HPMC K4M had positive significant effect on viscosity.So, it was concluded that viscosity incresed with increase the concentration of gellan gum and HPMC K4M.

Floating lag time Y₃ = + 24.62 +7.33 * X₁ +5.00* X₂

X₁ had a higher positive value than X₂. It was concluded that floating lag time increased with an increse the concentration of gellan gum compared to HPMC K4M.

Optimization of formulation batch:

Figure 4: Overlay plot for optimized batch

Based on input constraints the optimized in situ gel formulation was generated by the software which comprised of 0.50% w/v gellan gum and 0.60%w/v HPMC K4M.Optimized formulation was evaluated for % drug release at 6 h, viscosity and floating lag time. Drug release at 6 h, viscosity and floating lag time from optimized batch was found to be 68.02%,163.07 cps and 24.6 sec.

Stability study:

Optimized formulation did not show any significant changes when kept for 1 month. It indicates that formulation was found to be stable up to 1 month.

CONCLUSION:

The gastroretentive in situ gel of captopril successfully prepared for delivery of captopril into gastric region for 12 h. 3² full factorial design was employed to evaluate the effect of gellan gum and HPMC K4M on drug release, viscosity and floating lag time. From the 3²full factorial design it was concluded that as the concentration of gellan gum and HPMC K4M increases, viscosity and floating lag time increases, while drug release decreases. Drug release and viscosity could be adjusted by varying concentration of gellan gum and HPMC K4M.The in vitro drug release kinetic revealed that the Higuchi model is followed and drug release is by fickian diffusion. This study revealed that in situ gel can provide sustain release over extended period of time.

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Received on 13.06.2024 Revised on 16.10.2024

Accepted on 19.12.2024 Published on 01.07.2025

Available online from July 05, 2025

Research J. Pharmacy and Technology. 2025;18(7):3133-3138.

DOI: 10.52711/0974-360X.2025.00450

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