Formulation and Evaluation of Paroxetine Hydrochloride Loaded Thermoreversible In situ Intranasal Gel

Introduction

Depression is one of the leading causes of disability worldwide and leads to a significant health burden. It was reported that within a span of ten years, from 2005 to 2015, the number of cases of depression increased by 18%. It affects 322 million people worldwide, affecting nearly 4% of the population.¹

Depression is a condition of detestation and low mood; such activity can affect a person's feelings, thoughts, behavior, physical well-being, and circadian rhythm.²

Antidepressants are psychotropic drugs that are available in a wide range of dosages to treat mental conditions such as obsessive-compulsive disorder, clinical depression, anxiety disorders like panic, post-traumatic stress, social and serious phobias. Presently in US, the three top most used drug classes are antidepressants.³

There are two mainstays for treating depression: pharmacotherapy and psychotherapy. Selective serotonin reuptake inhibitors (SSRIs) are second-generation and first-line antidepressant drugs used to manage major depression.⁴

Paroxetine belongs to the SSRIs class of antidepressant agents. It is a potent and selective neuronal serotonin reuptake inhibitor, which has a little affinity towards β-adrenergic, muscarinic (α1, α2), dopamine (D2, 5-HT1, 5- and histamine (H1) receptors. Paroxetine expresses its action at the synaptic receptor and increases 5-HT in the CNS by inhibiting the reuptake of serotonin and boosting serotonergic neurotransmission by decreasing the production of a neurotransmitter. The dose of Paroxetine is 10-60 mg per day orally, with a plasma half-life of about 21 h, with <50% oral bioavailability due to hepatic first-pass metabolism.⁵

There is a need to develop an alternative drug delivery system for Paroxetine to bypass hepatic first-pass metabolism and increase bioavailability.

The intranasal route is one of the alternative routes for drugs that undergo extremely rapid first-pass metabolism. Delivery of the drug to the brain by this route is more advantageous than directly delivering the drug to the brain via the olfactory route.^6,7

The problem associated with the nasal route is nasolacrimal drainage. The dose instilled into the nose ultimately enters the pharynx and follows the same fate as that of the oral route. To tackle this problem, nowadays, in situ gelling systems have been developed wherein formulation remains in the sol phase at normal temperature but turns into gel when instilled into the nose due to higher temperature in the nasal cavity.

Thus, in the present work, an attempt was made to formulate a thermoreversible gel that provides sufficient viscosity and mucoadhesive strength to improve the residence time of the formulation in the nasal cavity. Further addition of mucoadhesive polymers increases the residence time of the formulation in the nose. The synergistic effect of these helps improve the performance of the formulation.

Materials and Methods

Paroxetine hydrochloride, Carbopol 934, and Poloxamer 407 were procured from Yarrow Chem. Products, Mumbai, and all other solvents and chemicals were obtained from authenticated sources.

Gelation temperature determination⁸

A visual inspection method was adopted to determine the gelation temperature. Poloxamer 407 solutions 15-20% w/v were prepared and measured. About 10 mL of each solution was kept on a hot plate magnetic stirrer, heating at 32–34º C. Gelation or transition temperature was noticed at 32-34º C, where rotation of the magnetic bead stopped due to gel formation. Different concentrations, i.e., 0.1–0.5% w/v of carbopol 934P in poloxamer 407 solution, at which gelation took place were used for further study.

Formulation of Paroxetine HCl in situ intranasal gel⁹

The formulation of Paroxetine HCl in situ intranasal gel was prepared by cold technique. Various batches of A1 to A5 were formulated as presented in Table 1. Carbopol 934P was dispersed completely in cold water to get solutions ranging from 0.1 to 0.5% w/v of Carbopol 934P. Poloxamer 407 was added to the above solutions in such a way that the final concentration of poloxamer in solution becomes 19% w/v. These gel systems were placed in cold conditions (4-8º C) overnight so that clear systems are obtained. Paroxetine HCl (0.5% w/v) was dissolved completely in the above gels. Formulated gels were then stored at 4°C until further evaluation.

Evaluation of in-situ gels

Physico-chemical parameters of Paroxetine HCl in situ gel

The physico-chemical parameters of formulated gels were evaluated for their pH, clarity, and drug content.

Clarity and pH¹⁰

The pH of the prepared gel was examined using a digital pH meter (EQ-614A, Equip-Tronics). The pH meter was calibrated before use with standard buffer solutions of pH 4 and 7. Then gel was taken in a beaker, and pH was recorded. The clarity of the gel was determined by the visual inspection method under white and black backgrounds.

Drug content determination¹¹

To determine drug content, 1 mL of each formulation was transferred into a 100 mL volumetric flask and then diluted with distilled water up to the mark. After suitable dilutions, the amount of drug in the formulation was measured by using UV spectroscopy at 293 nm (Shimadzu UV-1800, Japan).

Viscosity determination¹²

The viscosity of the prepared gel was determined using a Brookfield rheometer (Brookfield DV-I Prime Brookfield Engineering Laboratories. Inc.). The gel was transferred to a 100 mL beaker and maintained at the initial temperature of 10±1^oC, and then the rheometer was operated by using a 64 No. spindle at 50 rpm. The temperature was then gradually raised to 10^oC to attain the set temperature, and finally, viscosity was noted down.

Mucoadhesive strength determination¹³

The force required for gel detachment from the tissue of the nasal mucosa is known as mucoadhesive strength. A small piece of the nasal mucosa of prepared gel was used to determine the force required to detach the gel from nasal mucosal tissue. A piece of the nasal mucosa of a sheep was procured from the slaughterhouse at a local market. The mucosa and bone cartilage were separated, and then mucosal tissue was cut into small pieces. With the help of a thread, two pieces of tissue were tied to two separate glass slides. One glass slide was fixed to the bottom of the pan balance with tissue facing the downside. Another slide was fixed on a wooden platform of the balance with tissue facing upwards. Then, 100 mg of prepared gel was placed on the bottom slide, and the upper slide was brought into contact and held for two minutes to ensure tissue contact. Slowly, dummy granules were added to another pan until both tissue slides separated. The mucoadhesive strength of formulations A1 - A5 was measured and, detachment stress was expressed in dyne/cm2 .

Mucoadhesive strength = (m×g)/A×100

Where,

m = weight of granules required to separate the tissues,

g = acceleration due to gravity (980 cm/s2 ),

A = area of mucosa exposed 

In vitro drug release study¹⁴

A Franz diffusion cell was used to determine drug release from the gel. Artificial dialysis membrane (Mol wt12,000–14,000 Da) was soaked for 2 h in receptor medium before its use. Around 37 mL of phosphate buffer with pH 7.4 was placed in a receptor compartment. About 2.5 mg of gel, which is equivalent to a drug, was transferred into the donor compartment. Both compartments were separated by an artificial dialysis membrane. Throughout the study, the receptor medium temperature was maintained at 32±1o C. From the receptor compartment, 0.5 mL of the sample was withdrawn at definite time intervals until 8 h and replaced with an equal quantity of fresh buffer every time. The samples were analyzed by UV spectroscopy at 293 nm with suitable dilutions before analysis.

Ex vivo drug permeation evaluation¹⁵

The ex vivo permeation study was performed using a similar method as the in vitro study. In this study, artificial dialysis membrane was replaced with the nasal mucosa of the goat, and the duration of the study was 8 h. Freshly sacrificed nasal mucosa from the goat was collected from a slaughter shop at a local market and was immediately transferred into saline phosphate buffer of pH 7.4. The nasal septum was separated carefully from the bone to obtain mucus membrane and then washed thoroughly with saline phosphate buffer, pH 7.4.

Stability studies

Stability of gels was determined by keeping samples in glass vials and packed with aluminum foil to maintain air-tight conditions and samples were stored at 5°C ± 3°C for one month. After one month, samples were evaluated for drug content, gelation temperature, and physical characteristics.

Results

Gelation temperature determination

A visual inspection method was used to determine gelation temperature, and the results are presented in Table 2. A minimum concentration, i.e., 19% w/v of poloxamer 407 was required for the conversion of sol-gel at 32-34º C. About 0.3% w/v of carbopol 934P was found to be optimum for the mucoadhesive property of the gel. As the concentration of poloxamer 407 increased, the gelling temperature was found to have decreased. The higher concentration of polymer increased the swelling network structures that form gel at lower temperatures. Further addition of carbopol has decreased the gelling temperature, which could be attributed to its highly cross-linked polymeric network structure that gets hydrated and swells in the presence of water.

Drug content determination

The drug content of all the gels was determined by UV spectrophotometer and results were found to be in the range of 96.50 and 98.66%.

Viscosity determination

The viscosity of all the gels was determined using a Brookfield rheometer and the graphical presentation is shown in Figure 1.

Mucoadhesive strength determination

The detachment stress method was adopted to determine mucoadhesive strength, and the results are presented in Table 3. Formulations A2 to A5 have shown sufficient mucoadhesive strength ranging between 5,080.35 to 10,875.82 dynes/cm² , and the graphical representation is shown in Figure 2.

In vitro drug release study

The Franz diffusion cell and artificial dialysis membrane were used to determine drug release from the gel. Formulations A1 and A4 showed 86% and 87.13% drug release in 8 h, respectively, as presented in Table 4, and a graphical representation of this is shown in Figure 3. Thus, formulation A4 was selected as the optimized formulation for further ex vivo studies.

Ex vivo drug permeation evaluation

Franz diffusion cell and goat's nasal mucus membrane were used in ex vivo permeation study for optimized A4 formulation. The drug permeation of formulation A4 was found to be 82.3% for 8 h, and the results are presented in Table 5 and a graphical representation is shown in Figure 4.

Stability studies

Stability of gels was determined after one month, and samples were evaluated for various parameters like drug content, gelation temperature, and clarity. All formulations showed no change in gelation temperature. The drug content of all formulations was found to be in the range of 95 to 98.64%. All the formulations were found to be clear except A5. The formulation A5 was found to be opaque. The highest concentration of carbopol 934P in A5 may have resulted the density differences and changes in gel network structure, which is responsible for the opacity of the concerned formulation.

Discussion

The preliminary step in thermoreversible gel formulation is to determine the phase transition temperature. It is the temperature at which any system changes its form from one phase to another. In the case of thermoreversible gel, it is the conversion of sol to gel and vice versa. 

The thermoreversible gel should have a phase transition temperature between 25-34^oC. If it is below 25^oC, it may create issues for handling during manufacturing, and if it is above 34^oC, then it may retain its sol state at body temperature and wash away from the nasal cavity after installation. The results have indicated that 19% w/v poloxamer 407 solutions have a gelling temperature of 32-34^oC. The concentration below this did not showing any gelling. The negative coefficient of solubility of the block polymer of poloxamer 407 is responsible for its thermoreversible property. The rise in temperature results in an increase in micelle formation which gets tightly bound to form a gel. The addition of carbopol 934P has further decreased the transition temperature due to its gelling property.^16-17 Thus, based on the results obtained, 19% w/v poloxamer 407 and 0.3% w/v carbopol 934P were considered as optimized concentrations for the final formulation. The mucoadhesive property of carbopol 934P is associated with the presence of carboxylic groups in its structure. These groups form hydrogen bonds with sugar residue in oligosaccharide chains in mucus membrane, thus showing mucoadhesion. The mucoadhesive strength was found to increase with an increase in carbopol 934P concentration. It is obvious as the rise in concentration results in a rise in carboxylic groups which further increases hydrogen bonding and mucoadhesion.¹⁸ During ex vivo drug permeation studies, it was observed that drug permeation was slower for the initial 2 h (< 15%), but it increased significantly after 2 h (> 80% at 8 h). This is associated with the conformational changes in the polymer chain of carbopol resulting in relaxation of the gel network. Further swelling of the block polymer chain results in the relaxation of the gel network and increased permeation after 2 h.¹⁹ The formulations were found to be stable concerning to studied parameters.

Conclusion

The developed thermoreversible mucoadhesive in situ intranasal gel of Paroxetine HCl has shown increased residence time in the nasal cavity. Based on the results of in vitro and ex vivo studies, the A4 formulation was found to be optimum. Thus, the present work concluded that Paroxetine HCl in situ intranasal gel is safe as well as effective for treating depression.

Conflict of interest

None