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Technical Review Article | Open Access | Published 26th March 2026
Transdermal Drug Delivery System: An Innovative Method for Regulated Drug Release
Pravin Kumar Sharma* | EJPPS | 311 (2026) https://doi.org/10.37521/ejpps31106
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Abstract
Transdermal drug delivery system (TDDS) is a system that allows slow and controlled release of the drug in a fixed quantity. This method is beneficial for several reasons, such as the drug shows high bioavailability, a longer duration of action, fewer side effects, and medicines need not be taken repeatedly, which makes treatment easier. It can also be stopped whenever desired. A big advantage of TDDS is that this method is painless. Many evaluation parameters are used to test this system, such as weight of the patch, thickness, amount of medicine, moisture content, bending strength and penetration of drug on the skin.
Smart patches, nanotechnology and mobile controlled technologies are being developed in TDDS. Overall, TDDS is a safe, comfortable and modern method of drug delivery that may become a better alternative to oral and injection dosage in the future.
Keywords: Transdermal drug delivery system, controlled release, painless administration, smart patches, bioavailability.
Introduction
TDDS also known as “patches," are dosage forms that allow drugs to enter the body via the skin. The drug is released slowly into the body in a fixed amount, resulting in a long-lasting effect. When a drug has to be delivered into the body through the skin, it is important to take into account the structure of the skin, its physical and chemical properties. The biggest advantage of the transdermal system is that it avoids the first pass metabolism process that usually happens in orally administered drugs. Also, it is easy to use, so patients do not have any problems in taking the medicine and they take the medicine on time. Traditional oral dosage forms such as tablets or capsules need to be taken multiple times a day at fixed times and in the correct doses. This causes a number of problems, such as the inconvenience of taking the medicine repeatedly, forgetting the medicine, risk of overdose if the medicine is taken before time, fluctuation in the amount of medicine in the body, low patient compliance etc. To avoid these problems, transdermal patches have become a good option. It is an easy method, which anyone can apply themselves and it releases the drug slowly (Kumar et al., 2009, Kandavilli, S., et.al 2010).
Advantages of TDDS
The following are some benefits of transdermal delivery systems-
There is no need to take the medicine again and again, with the result that the patient takes the medicine on time and the treatment is better with improved patient compliance.
The drug goes directly into the blood, with the result that it does not get degraded by going to the liver first (first pass metabolism is avoided).
If the medicine is causing any adverse effects administration of the medicine can be stopped immediately by removing the transdermal patch.
The time of administration of the medicine is fixed and easy, which makes it simpler for the patient to take the medicine and the effect is the same in all patients (Sharma et al., 2011, Ghosh et al., 2010).
Limitations of TDDS
It is impossible to provide a medication that requires high blood levels, and it may even irritate or sensitise the skin.
The adhesives could be difficult to wear and might not stick to all skin types.
A significant obstacle to the product's widespread popularity is its high price.
The skin can only transmit tiny lipophilic medications easily.
Hypersensitivity responses and skin inflammation are possible.
Unsuitable for large dosages of drugs (Sharma et al., 2011, Prausnitz and Langer, 2006).
ANATOMY OF SKIN
The skin surface of a normal adult human is approximately two square metres and is capable of absorbing about one-third of the blood circulating in the body. The skin is a multi-layered organ that is structurally divided into three main layers: the epidermis, dermis, and hypodermis, as shown in figure 1. These layers are composed of different tissue properties and together provide protection, coverage, and protection to the skin. The epidermis is the outermost layer of the skin, which brings the body in direct contact with the external environment. When viewed under a microscope, the epidermis is divided into five sublayers, in which the topmost layer is the stratum corneum. This layer is in direct contact with the outside world and plays an important role in protecting the body (Kim et al., 2001, Roberts, 1997).
Epidermis
The epidermis is the outermost layer of the skin, which provides protection to the body from the external environment. This layer acts as a barrier to prevent water loss, infection, and external damage. Cells known as keratinocytes, which produce the strong and protective protein keratin, make up the majority of the epidermis. This layer mainly consists of the stratum corneum (outer layer) and the base layer (inner layer). The epidermis also plays an important role in skin colour (pigmentation) and regeneration of new cells (Cevc and Blume, 1992, Brown et al., 2006).
Dermis
The thick inner layer of the skin, known as the dermis, is situated immediately underneath the epidermis. This layer is made up of important components such as connective tissue, sweat glands, hair roots, blood vessels, and nerve endings. The dermis gives the skin its strength, suppleness, and nourishment. This layer also plays an important role in regulating body temperature and feeling sensations (Verma and Pathak, 2010, Gaikwad, 2013).
Hypodermis
The subcutaneous layer, also called the hypodermis, is the deepest layer of the skin. This layer, which is composed of connective tissue and fat, aids in temperature regulation and shock absorption. This layer connects the skin to the muscles and bones underneath. The hypodermis shields the body from mechanical harm and stores energy (Rulea et al., 2016).
MECHANISM OF PERMEATION
A systemically active drug must have specific physico-chemical characteristics for absorption and uptake by the capillary network in the dermal papillary layer, expressed as dQ/dt.
dQ/dt = Ps (Cd-Cr)…………1
Where, Cd and Cr are, respectively, the concentrations of skin penetration in the donor phase (stratum corneum) and the receptor phase (systemic circulation); and Ps is the total permeability coefficient of the skin and is described by
Ps = Ks Dss / Hs……………...2
In which, Ks is the penetration's partition coefficient, Dss is apparent diffusivity of the penetrant, and Hs is the skin's thickness.
Given that the Ks, Dss, and Hs components in equation (2) are constant for the specified set of circumstances, the permeability coefficient (PS) may thus be a constant. If Cd>Cr, a constant rate of drug penetration is attained, and equation (1) may be simplified to
dQ/dt = Ps.Cd ……………………….3
If the Cd value stays relatively constant during the skin permeation process, the rate of skin permeation (dQ/dt) also becomes constant. Making the drug release at a rate (Rr) that is consistently higher than the rate of skin absorption (Ra), that is, Rr >> Ra, is essential to maintaining the Cd at a constant value.
This maintains the drug concentration on the skin surface (Cd) at a level that is consistently higher than the drug's equilibrium (or saturation) solubility in the stratum corneum (Cse), meaning that Cd >> Cse; also, it sets a maximum rate of skin penetration (dQ/dt) m, is therefore obtained as stated by equation 4.
(dQ/dt)m= Ps Cse………..4
It appears that the drug's skin permeability coefficient (PS) and equilibrium solubility in the stratum corneum (Ces) dictate the magnitude of (dQ/dt)m (Mali et al., 2015, Yadav, 2012, Chien, 1987, Arunachalam et al., 2010).
TYPES OF TDDS
Reservoir type
In this system the drug is contained in a reservoir (storage chamber) which slowly releases the drug onto the skin. A regulating membrane covering this reservoir controls the rate of medication release. It has very precise delivery characteristics and long-lasting effects. However, its structure is rather complex e.g. Nitro-glycerine patch.
Matrix type
This involves mixing the drug with a polymer matrix, which is a sticky material. When the patch is applied to the skin the drug is released slowly. It is easy to make and cheap. Drug release is not controlled by the membrane but is released slowly from the matrix e.g. Diclofenac patch.
Adhesive dispersion type
In this, the medicine is mixed in the adhesive itself. It adheres to the skin and releases the medication. Its texture is thin and flexible. It is suitable for small and short-term use patches e.g. Nicotine patch.
Micro-reservoir type
This is a mixture of both reservoir and matrix. The drug is stored inside the gel in the form of micro particles. It permits a controlled and extended release of the medication. It is a complex but effective system e.g. Hormone patches (Shaikh and Srivastava, 2024, Rastogi and Yadav, 2012).
METHODS OF PREPARATION OF TDDS
There are many ways to prepare a TDDS. Important preparation methods are described below:
Solvent casting method
This involves dissolving the drugs and polymer in a solvent, such alcohol or chloroform. A thin coating (film) is created by pouring this solution over a level surface and allowing it to dry. This is the simplest and most common method to create a TDDS.
Melt extrusion method
The melt extrusion method involves heating and melting the medication and polymer together, after which it is extruded from a specialized machine and shaped into a thin sheet or film. This procedure involves a device known as a hot melt extruder, as shown in figure 2. Since this procedure doesn't require a solvent, it is environmentally friendly. To provide the final shape of the patch, the medicine and polymer are combined, heated, and processed together using the hot melt extruder.
Direct milling method
This involves mixing the drug and polymer in a machine without the need of a solvent. After that, a patch is formed by rolling the resulting mixture. When the medicine is unstable in the solvent, this approach can be helpful.
Adhesive dispersion method
This involves combining the drug and adhesive. After that, this mixture is introduced to a backing material (such as paper or film) to form a patch. For thin, flexible patches, this works well (Pamu et al., 2014, Dhurve et al., 2024).
EVALUATION PARAMETERS OF TDDS
Evaluation parameters of TDDS are used to ensure that the patch is working properly. The main evaluation parameters that are used to check the quality, stability, and functionality of a TDDS are listed below:
Physical evaluation
The thickness, colour, flexibility, smoothness, and uniformity of the patch are checked. This ensures that the patch is consistent in appearance and easy to use.
Drug content uniformity
The amount of drug in each patch should be the same. If the medicine is less or more then its effect will also decrease or increase. This is measured using a UV-spectrophotometer or HPLC.
Moisture content
This is the measure of total moisture present in the patch. Too much moisture can spoil the medicine and the patch will not stick to the skin.
Folding endurance
The patch is folded several times at the same location to see if it tears or not. If it breaks quickly, it will not be usable.
Weight variation
The weight of each patch is measured. All patches must weigh approximately the same so that the dose remains consistent.
Tensile strength
The patch is stretched to see how much force it can withstand without tearing. This determines its strength and durability.
Drug release rate
This measures how much and how quickly/slowly the drug is released from the patch. This determines how the drug will show its effect.
In-vitro skin permeation (penetration of medicine through the skin)
It is observed in the laboratory how much medicine is penetrating inside the skin. A Franz diffusion cell and artificial or animal skin membrane is used to determine this parameter.
Skin irritation test
The patch is applied to the skin to see if there is any irritation, itching or allergy. This test is necessary for safe use (Deepthi, et al., 2022, Pandey and Gupta, 2023).
FACTORS INFLUENCING TDDS
Age of skin
Young and adult skin is more porous than elderly, but children's larger surface area per body weight leads to harmful effects from steroids, boric acid, and hexachlorophene (Shingade et al., 2012).
Skin health
Skin acts as a barrier, but substances can still pass through. Solvents such asand methanol and chloroform create artificial shunts, allowing drug molecules to flow through the horny layer (Patel and Shah, 2018).
Skin hydration
The hydration of skin increases its permeability for medication molecules, enlarges its tissues, and relaxes wrinkles when saturated with water (Rastogi and Yadav, 2012).
Sunlight
In sun-exposed regions, sunlight produces bruising, mild damage, and weakening of blood vessel walls, and thus affects the permeability of medicines (Chankhore et al., 2024).
FUTURE PROSPECTS
The future prospects of TDDS are going to become more widespread and useful in the coming years. This technology will allow many new drugs such as hormones, anticancer, antidiabetics and antipsychotic drugs to be delivered through the skin. Smart patches are being developed in TDDS, which will release the drug in a controlled manner according to the body's need. Some patches can also be controlled by mobile apps, making it easier to administer and monitor the drug. With the help of nanotechnology and microneedle technology, both the penetration and effect of the drug will improve. Gene and protein-based treatments can also be given through TDDS, which was previously possible only through injection. With research and technological development, TDDS is becoming more advanced. It can become a better alternative to oral and injection dosage in the future. TDDS has the potential to bring a revolutionary change in the world of drug delivery (Dwivedi et al. 2025, Hardiya et al. 2024, Mahajan et al., 2021).
Conclusion
The TDDS is effective method, which can transfer the drug gradually via the skin into the body. This method is painless and the patient does not need to take the medicine repeatedly, thereby improving compliance. This system avoids first pass metabolism thereby increasing the efficacy of the drug. The drug release is controlled and stable with no fluctuations in plasma levels. The use of a TDDS is more useful in long term diseases. There are many types of tests that are used to check its quality, such as thickness and weight determination, amount of medicine present, etc. In the future, smart patches, nano technology and mobile controlled patches will make its use even easier. This system is especially useful for children, the elderly and mentally ill patients. Thus, TDDS will emerge as a safe, convenient and better option in times to come.
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Author Information
Authors: Dr. Pravin Kumar Sharma
Corresponding Author:
Dr. Pravin Kumar Sharma
Professor
Acropolis Institute of Pharmaceutical Education and Research, Indore (M.P.), India
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