When it comes to Transdermal Drug Delivery Systems (TDDS) in the context of Novel Drug Delivery Systems (NDDS), a variety of formulation approaches have been developed to optimize and control the delivery of drugs across the skin barrier.
The goal is to ensure effective drug delivery, prolonged therapeutic effects, and reduced side effects.
Here are some of the primary formulation approaches for TDDS:
1. Monolithic Matrix Systems:
In these systems, the drug is uniformly dispersed throughout a polymer matrix.
As the matrix comes in contact with the skin, the drug diffuses out and permeates the skin.
The release rate often depends on the drug's solubility in the matrix, the matrix's thickness, and the drug's diffusion coefficient.
2. Reservoir Systems:
The drug is enclosed in a reservoir between a backing layer and a rate-controlling membrane.
The drug diffuses through the rate-controlling membrane and then permeates the skin.
This approach offers more controlled and consistent drug delivery compared to matrix systems.
3. Drug-in-Adhesive Systems:
The drug is directly dispersed in an adhesive polymer.
When the adhesive side contacts the skin, the drug begins its permeation.
Simplicity in design and fewer components make this system attractive. However, the adhesive must be compatible with the drug, and not all drugs are suitable for this method.
4. Microreservoir Systems:
This system is a combination of the matrix and reservoir systems.
The drug solution or suspension is sealed in microscopic reservoirs and dispersed in a polymer matrix.
This allows for controlled release of the drug while overcoming some limitations of the reservoir systems.
5. Microneedles:
Tiny needles that create micro-channels in the skin to facilitate drug delivery.
They bypass the stratum corneum, delivering the drug to the deeper layers of the skin or systemic circulation.
Microneedles can be made of biodegradable polymers that release the drug as they dissolve.
6. Vesicular Systems:
These involve entrapping the drug in vesicles like liposomes, ethosomes, or transferosomes.
The vesicles facilitate the delivery of both hydrophilic and lipophilic drugs through the skin.
For instance, transferosomes can deform and pass through narrow constrains in the skin, making them particularly effective.
7. Nano-based Systems:
Use of nanoparticles, nanoemulsions, or nanocapsules to deliver drugs.
The small size and large surface area can enhance the solubility of poorly soluble drugs and improve their permeation through the skin.
8. Gel-Based Systems:
Incorporation of drugs in gels (hydrogels or organogels) that can be applied to the skin.
These systems are non-occlusive and can be designed to provide prolonged drug release.
9. Incorporation of Permeation Enhancers:
As previously discussed, these agents can be added to the formulation to enhance the skin permeability and improve drug delivery.
10. Patch Pre-treatment Systems:
Techniques like iontophoresis, sonophoresis, or laser ablation can be used before applying a transdermal patch to enhance skin permeability.