Preformulation Studies For Transdermal Drug Delivery System

Abstract

Rheumatic disease is one of the most common inflammatory conditions in developing countries and a leading cause of disability. Conventional treatments for rheumatoid arthritis and related conditions typically involve analgesics and nonsteroidal anti-inflammatory drugs (NSAIDs). Ketoprofen, a potent NSAID that inhibits prostaglandin synthetase-cyclooxygenase, is widely used in the management of rheumatoid arthritis. However, long-term use of Ketoprofen carries the risk of undesirable systemic side effects and gastrointestinal irritation.

Introduction

The primary objective of any drug delivery system is to ensure the delivery of therapeutic drug levels to the target site within the body, achieving and maintaining the desired drug concentration promptly.

Traditional drug delivery methods such as tablets, capsules, pills, and injections may not always be suitable for delivering therapeutic compounds produced through modern technology¹. The concept of controlled drug release through the skin as a point of entry has gained popularity due to several compelling reasons. The skin, being one of the largest and easily accessible organs of the human body, presents a unique opportunity for drug delivery.

In response to this innovation, various Transdermal Drug Delivery Systems (TDDS) have emerged. Achieving controlled and sustained drug delivery into the systemic circulation through the skin involves the use of a suitable rate-controlling membrane and drug reservoir. The permeability of drugs through polymeric free films depends on the characteristics of the polymer, casting solvent, and plasticizer². Polymers such as Eudragit L 100, Hydroxypropyl methyl cellulose (HPMC), Ethyl cellulose (EC), Carboxymethyl cellulose (CMC), and Polyethylene glycol (PEG) have been utilized as matrix films to provide a suitable lattice structure and achieve satisfactory drug release and diffusion.

Enhancers like Dimethyl sulfoxide (DMSO) and Propylene glycol have also been employed to facilitate transdermal drug delivery. Various categories of drugs have been formulated into Transdermal films, using different combinations of polymers and enhancers, to create controlled and sustained drug delivery systems³.

Ketoprofen stands out as one of the most potent cyclooxygenase inhibitors, with concentrations well within the therapeutic plasma range (EC₅₀ 2 μg/l). Furthermore, Ketoprofen is a robust inhibitor of bradykinin, a significant chemical mediator of pain and inflammation. It also stabilizes lysosomal membranes against osmotic damage and prevents the release of lysosomal enzymes that contribute to tissue damage in inflammatory reactions. Ketoprofen is readily absorbed from the gastrointestinal tract, with peak plasma concentrations occurring approximately 0.5 to 2 hours after administration. Approximately 99% of Ketoprofen is bound to plasma proteins, and substantial drug concentrations are found in the synovial fluid. The time to reach maximum plasma concentration (T_max) ranges from 60 to 90 minutes. Food does not significantly affect the bioavailability of Ketoprofen, but it does slow down the rate of absorption.

Methods

Preformulation Studies

Preformulation studies encompass the phase of formulation development in which the physical properties of the drug substance are characterized. These properties are crucial for the formulation of a stable, effective, and safe dosage form. Additionally, potential interactions with various inert ingredients intended for use in the final dosage form are also considered. In this research, several preformulation studies were conducted, including solubility testing, determination of partition coefficient, calibration curve development, compatibility studies, and differential scanning calorimetry.

A. Determination of Melting Point

The melting point of the Ketoprofen sample was determined using the Thiele's tube method. A fine powder of Ketoprofen was loaded into a capillary tube, previously sealed at one end, and the capillary tube was affixed to the bottom of a thermometer. The thermometer, along with the capillary tube, was immersed in liquid paraffin contained in a tube. The bottom of the tube was gently heated using a burner. The melting point was recorded when the sample began to melt.

B. Solubility Studies

Solubility studies were conducted by adding the solute incrementally to a fixed volume of solvent. After each addition, the system was vigorously shaken, and visually examined for any undissolved solute particles. The point at which some of the solute remained undissolved served as a rapid estimate of solubility, based on the total amount added up to that point.

C. Determination of Partition Coefficient

The partition coefficient study was carried out using n-octanol as the oil phase and phosphate buffer at pH 7.4 as the aqueous phase. Equal volumes of the two phases were mixed and saturated with each other using a mechanical water bath shaker at 32°C for 24 hours. The saturated phases were separated through centrifugation at 2000 rpm using a Remi Centrifuge. Standard plots of the drug were prepared from both the phosphate buffer and octanol. In triplicate, equal volumes of both phases (10ml each) were taken in conical flasks, and 100mg of the weighed drug was added to each. The flasks were agitated at 32°C for 6 hours at 100rpm to achieve complete partitioning. The two phases were then separated by centrifugation at 100rpm for 5 minutes, and their respective drug contents were analyzed. The drug's partition coefficient, Ko/w, was calculated using the following formula:

^{Concentration in octanol}

^{Ko/w =}

^{Concentration in phosphate buffer pH 7.4}

D. Development of Calibration Curve for Ketoprofen (max)

A stock solution of Ketoprofen was prepared by dissolving 100mg of the drug in 100ml of phosphate buffer at pH 7.4. From this solution, 10ml was taken and diluted to 100ml. Subsequently, dilutions of 5, 10, 15, 20, and 25 g/ml were prepared using phosphate buffer at pH 7.4. The maximum absorption (λ_max) of the drug was determined using a UV-visible spectrophotometer, with an absorption maximum of 260nm selected. At this wavelength, the absorbance of all other solutions was measured against a blank.

E. FTIR Study

An FT-IR spectroscopy study was conducted to assess the compatibility between Ketoprofen and the polymer Hydroxypropyl methyl cellulose. Spectra were separately scanned for the pure drug and the drug with excipients. Pellets were prepared using a potassium bromide press, and the spectra were compared to confirm the presence of peaks.

F. Differential Scanning Calorimetry (DSC)

Dynamic DSC studies were carried out on both the pure drug and the drug-loaded patch. The obtained thermograms are presented in Figure 5.3. Data obtained from the DSC scans for Ketoprofen and the Ketoprofen-loaded patch are provided in terms of onset of melt (To), melting points (Tm), and completion of melt (Tc).

Results

Preformulation Studies

Preformulation studies are essential for gaining insights into the physicochemical properties of the drug and assessing compatibility with the other excipients used in the formulation. Below are the results of various preformulation characterizations.

A. Determination of Melting Point

The melting point of Ketoprofen was determined to be 93.5°C.

B. Solubility Studies

Ketoprofen exhibits excellent solubility characteristics. It is freely soluble in phosphate buffer at pH 7.4, ethyl alcohol, methyl alcohol, chloroform, acetone, dichloro methane, but remains insoluble in water.

C. Determination of Partition Coefficient

The partition coefficient studies were conducted in triplicate, resulting in an experimentally determined partition coefficient (P) value of 0.840. These findings suggest that the drug possesses sufficient lipophilicity, meeting the requirements for formulating the selected drug into a transdermal film. The biphasic nature of the drug closely resembles the biphasic nature of the skin, thereby ensuring efficient penetration through the skin.

E. Development of Calibration Curve for Ketoprofen (λ_max)

The absorption maximum (λ_max) of Ketoprofen was determined to be 260nm.

Table 1: Calibration Curve for Ketoprofen in pH 7.4 Phosphate Buffer

Sl. No.	Concentration (in µg/ml)	Absorbance	Peak Area ± S.D Mean*	R2 Value
1.	0.9998
2.	5	0.1540 ± 0.0016
3.	10	0.3097 ± 0.0022
4.	15	0.4504 ± 0.0021
5.	20	0.6113 ± 0.0103
6.	25	0.7561 ± 0.0038	Standard deviation, n = 3

*Standard deviation, n = 3

G. FT-IR Study

FT-IR analysis was employed to assess the compatibility of Ketoprofen with the polymer hydroxypropyl methyl cellulose. The spectra of both the pure drug and the drug with excipients were compared to identify common peaks. It was observed that the specific peaks of the pure drug and the formulation exhibited no significant variation in height, intensity, or position. This confirmed the compatibility of the drug with the excipients, indicating that there was no interaction between the drug and the polymer.

Table 2: FTIR Spectra Data of Ketoprofen and Ketoprofen Patch

Assignment	Band Position of Pure Drug (cm-1)	Band Position of Formulation (cm-1)
C - H Stretching of CH3 Group (Asymmetric) Masked by O-H Stretching	2970, 2930	2978, 2938
C - H Stretching of CH3 Group (Symmetric) Masked by O-H Stretching	2880	2876
C = O Stretching of Acid	1695	1693
C = O Stretching of Ketone	1655	1649
C = C Stretching of Aromatic Ring	1595	1599
C - H Deformation of CH3 Group (Asymmetrical)	1440	1442
C - H Deformation of CH3 Group (Symmetrical)	1370	1369
C - H Deformation of Aromatic Ring	860-690	825 - 640

From the FTIR studies, the characteristic absorption bands for the important functional groups of the pure drug, empty patch, and drug-loaded patch were identified. The data provided in Table 2 illustrate that the absorption bands of Ketoprofen remained consistent after successful drug loading, with no changes in their positions. This indicates that there were no chemical interactions between the drug and hydroxypropyl methyl cellulose (HPMC). The findings align with those reported by Gary G et al., as our data agrees with their conclusions.

F. Differential Scanning Calorimetry (DSC)

To assess the compatibility of the drug, DSC studies were conducted on both the pure drug and the drug-loaded patch. The obtained thermograms are shown in Figure 3. The melting point of HPMC is within the range of 190-200°C, while the drug Ketoprofen has a melting point between 93-95°C. Ketoprofen exhibited a sharp endothermic peak at 93.02°C. Importantly, the presence of an endothermic peak at 95.46°C in the drug-loaded patches indicates that the drug is distributed within the patch without undergoing degradation and remains compatible with HPMC. The melting points of the drug and HPMC, as estimated from the DSC data, align well with our experimental findings.

Table 3: DSC Thermogram Data of Ketoprofen and Ketoprofen Patch

Formulation	To (°C)	Tm (°C)	Tc (°C)
Ketoprofen Drug	92.24	93.02	95.04
Ketoprofen Film	94.32	95.46	96.00

Discussion

Preformulation Studies

Preformulation studies are crucial for comprehending the physicochemical properties of the drug and assessing the compatibility of the excipients employed in the formulation. The results of these preformulation characterizations are discussed below.

A. Determination of Melting Point

The melting point of Ketoprofen was determined to be 93.50°C.

B. Solubility Studies

Ketoprofen exhibited excellent solubility characteristics. It was found to be freely soluble in phosphate buffer at pH 7.4, ethyl alcohol, methyl alcohol, chloroform, acetone, dichloro methane, while remaining insoluble in water.

C. Determination of Partition Coefficient

The obtained partition coefficient (P) value suggests that Ketoprofen possesses adequate lipophilicity, meeting the requirements for formulating the drug into a transdermal film. This biphasic nature of the drug mirrors the biphasic nature of the skin, facilitating efficient penetration through the skin.

D. Development of Calibration Curve for Ketoprofen (λ_max)

The absorption maximum (λ_max) was determined to be 260nm, confirming the purity of the Ketoprofen sample.

E. FT-IR Study

FT-IR analysis confirmed the compatibility of Ketoprofen with hydroxypropyl methyl cellulose (HPMC). The spectra of Ketoprofen and Ketoprofen patch showed no significant variation in peak height, intensity, or position, indicating compatibility between the drug and excipients. No physical or chemical interactions were observed between the drug and the polymer. The results align with the conclusions of Gary G et al.

G. Differential Scanning Calorimetry (DSC)

DSC studies provided evidence of the compatibility of the drug with the excipients. The presence of an endothermic peak at 95.46°C in the drug-loaded patches indicates uniform distribution of the drug within the patch, without degradation. The melting points of the drug and HPMC, as determined from the DSC data, corresponded well with experimental findings. These results are in agreement with the conclusions of Gary G et al.

Conclusion

A matrix-type transdermal drug delivery system for Ketoprofen was successfully fabricated using hydroxypropyl methyl cellulose through the solvent casting method. Various formulations of Ketoprofen were prepared using PEG 400 as a plasticizer and DMSO as a permeation enhancer to improve drug penetration. Physicochemical parameters, including uniformity of weight, uniformity of thickness, tensile strength, percentage elongation, folding endurance, percentage moisture absorption, percentage moisture loss, drug content, and scanning electron microscopy, were characterized in this study.

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