Editing Transdermal patch (section)

== Types ==
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[[File:Transdermal patches.jpg|right|thumbnail|Sample transdermal patches. On left is a 'reservoir' type, on the right a 'Single-layer Drug-in-Adhesive' version. Both contain exactly the same active ingredient with identical release rates.]]
There are five main types of transdermal patches.

=== Single-layer drug-in-adhesive ===
The adhesive layer of this system also contains the drug. In this type of patch the adhesive layer not only serves to adhere the various layers together, along with the entire system to the skin, but is also responsible for the releasing of the drug. The adhesive layer is surrounded by a temporary liner and a backing. It is characterized by the inclusion of the drug directly within the skin-contacting adhesive placed onto the epidermis.

=== Multi-layer drug-in-adhesive ===
The multi-layer drug-in-adhesive patch is similar to the single-layer system; the multi-layer system is different, however, in that it adds another layer of drug-in-adhesive, usually separated by a membrane (but not in all cases). One of the layers is for immediate release of the drug, and the other layer is for controlled release of the drug from the reservoir. This patch also has a temporary liner-layer and a permanent backing. The drug release from this depends on membrane permeability and diffusion of drug molecules.

=== Reservoir ===
Unlike the single-layer and multi-layer drug-in-adhesive systems, the reservoir transdermal system has a separate drug layer. The drug layer is a liquid compartment containing a drug solution or suspension separated by the adhesive layer. The drug reservoir is totally encapsulated in a shallow compartment molded from a drug-impermeable metallic plastic laminate, with a rate-controlling membrane made of a polymer like [[vinyl acetate]] on one surface.<ref name=":0">{{Cite web |date=2022-05-03 |title=Using transdermal patches safely in healthcare settings |url=https://www.sps.nhs.uk/articles/using-transdermal-patches-safely-in-healthcare-settings/ |access-date=2023-11-13 |website=Specialist Pharmacy Service (SPS), NHS |language=en-GB}}</ref> This patch is also backed by the backing layer. In this type of system the rate of release is zero order. Reservoir patches should not be cut (with the exception of hyoscine hyrdobromide 1.5mg patch according to the [[British National Formulary for Children]]).<ref name=":0" /><ref>{{Cite web |title=Hyoscine hydrobromide Medicinal forms |url=https://bnfc.nice.org.uk/drugs/hyoscine-hydrobromide/medicinal-forms/#transdermal-patch |access-date=2023-11-13 |website=NICE}}</ref>

=== Matrix ===
The matrix system has a drug layer of a semisolid matrix containing a drug solution or suspension. The adhesive layer in this patch surrounds the drug layer, partially overlaying it. The release rate is determined by the physical properties of the matrix.<ref name=":0" /> Also known as a monolithic device. Limited research indicates that it may be possible to cut some matrix patches to provide lower doses, provided the cut part not immediately used is stored at cool temperatures.<ref>{{Cite journal |last1=Ankarberg-Lindgren |first1=Carina |last2=Gawlik |first2=Aneta |last3=Kriström |first3=Berit |last4=Mazzanti |first4=Laura |last5=Ruijgrok |first5=Elisabeth J. |last6=Sas |first6=Theo C. J. |date=April 2019 |title=Estradiol matrix patches for pubertal induction: stability of cut pieces at different temperatures |journal=Endocrine Connections |volume=8 |issue=4 |pages=360–366 |doi=10.1530/EC-19-0025 |issn=2049-3614 |pmc=6454296 |pmid=30851161}}</ref>

=== Vapour patch ===
In a vapour patch, the adhesive layer not only serves to adhere the various layers together but also to release vapour. Vapour patches release essential oils for up to 6 hours and are mainly used for decongestion. Other vapour patches on the market improve quality of sleep or aid in [[smoking cessation]].