Transdermal drug delivery systems (TDDS) are specialized formulations designed to deliver drugs through the skin into the systemic circulation.
The basic components of these systems vary depending on the type of transdermal system, but generally, they include the following:
1. Drug:
The active pharmaceutical ingredient (API) intended for delivery to achieve therapeutic effects.
The drug must possess certain characteristics like appropriate molecular weight, lipophilicity, and potency to be suitable for transdermal delivery.
2. Matrix or Reservoir:
This is where the drug is stored within the patch.
Matrix System: The drug is uniformly dispersed in a polymer matrix. The drug releases and diffuses out of the matrix over time.
Reservoir System: The drug is stored in a liquid reservoir between a backing layer and a rate-controlling membrane. The drug diffuses through the membrane to the skin at a controlled rate.
3. Backing Layer:
The outermost layer of the patch.
Protects the patch from external factors and prevents the loss of drug or excipients.
Usually made of impermeable materials like polyester or polyethylene to ensure drug delivery only through the skin.
4. Rate-Controlling Membrane (specifically for reservoir systems):
Regulates the rate at which the drug is released from the reservoir to the skin.
Ensures a steady, controlled delivery of the drug over an extended period.
5. Adhesive Layer:
Ensures the patch remains attached to the skin.
Provides an intimate contact between the patch and the skin to facilitate drug transfer.
Should be hypoallergenic to minimize skin reactions.
6. Permeation Enhancers:
As discussed earlier, these are agents that facilitate or enhance the penetration of drugs through the skin.
Can be included in the formulation to improve the efficiency of drug delivery.
7. Release Liner:
A protective layer that covers the adhesive side of the patch.
Removed and discarded just before the patch is applied to the skin.
Usually made of materials like polyester, which are easily peeled off without disturbing the formulation.
8. Other Excipients:
These can include stabilizers, antioxidants, solvents, and other additives that serve various roles:
Stabilize the drug.
Modify the release rate
Enhance solubility.
Preserve the formulation.
Provide an acceptable appearance and feel.
A well-designed TDDS ensures optimal drug delivery over a specified period, maximizing therapeutic benefits while minimizing potential side effects. The selection and combination of the above components are pivotal in achieving the desired pharmacokinetic profile and therapeutic outcomes.