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A transdermal patch (Figure 13.8) contains a certain amount of drug and delivers it in a quantity which is sufficient to cause the desired pharmacological effect when it crosses the skin and into the systemic system.

Figure 13.8 Transdermal patches.

Three types of transdermal patch are available.

Adhesive

These are simply designed patches which consist of a drug-containing adhesive and a backing material. These patches do not provide much control over the rate of delivery and in most cases the stratum corneum controls the rate (Hillery et al. 2001).

Layered or matrix patches

Layered patches consist of a drug-containing matrix, an adhesive layer and a backing material. The drug-containing matrix controls the release of drug from the system (Hillery et al. 2001).

Reservoir

Reservoir patches consist of an enclosed reservoir of drug, a membrane layer, an adhesive layer and a backing material. The membrane layer controls the rate of drug delivery from the reservoir of drug.

Drugs which can be delivered in a transdermal system include fentanyl, hyoscine, nicotine and oestradiol (Hillery et al. 2001).

Evidence-based approaches

The advantages of transdermal systems are the avoidance of the presystemic metabolism, the drug effects can be maintained within the therapeutic window for longer which reduces side-effects and maintains constant dosing, there can be improved patient compliance and drug effects can be stopped with the withdrawal of the patch and the avoidance of the first-pass metabolism (Hillery et al. 2001). First-pass metabolism occurs when a drug passes through the digestive system and enters the hepatic portal system and the liver before it reaches the rest of the body. The liver metabolizes many drugs, thus reducing their bio-availability before reaching the rest of the circulatory system (Hardman et al. 1996).

A disadvantage of transdermal systems is the limited number of drugs for which the system is suitable; for example, drugs have to have a suitable potency to allow them to absorb across the skin and cause an effect. Tolerance-inducing drugs would need a period during which they were not administered, which is not always possible with transdermal systems. In addition, drugs to be used in transdermal systems cannot be irritating to the skin otherwise they would not be tolerated by patients (Hillery et al. 2001).

Preprocedural considerations

Specific patient preparations

The condition of the affected site should be assessed for altered skin integrity as applying medicines to broken skin could cause too rapid absorption, resulting in systemic effects (Cherneck et al. 2002, Snyder 2007). The affected area must be washed and dried before applying the patch, which should be attached to hairless areas of skin. The upper chest, upper arms and upper back are recommended sites and the distal areas of extermities should be avoided (Chernecky et al. 2002). Patches should not be trimmed or cut. Contact with water does not affect the patch (Chernecky et al. 2002).

Procedure guideline 13.5 Medication: transdermal applications

Essential equipment

Transdermal patch

Preprocedure

Action Rationale

1 Explain and discuss the procedure with the patient. To ensure that the patient understands the procedure and gives their valid consent (Griffith and Jordan 2003, E; NMC 2008b, C; NMC 2008c, C).

2 Check the patient’s prescription chart and the patient’s identity. To ensure that the patient is given the correct drug and dose (NMC 2008a, C).

Procedure

3 Close room door or curtains if appropriate. To ensure patient privacy and dignity. E

4 Assist the patient into the required position. To allow access to the affected area of skin. E

5 Assess the condition of the skin and do not apply to skin that is oily, burnt, cut or irritated in any way. To prevent local or systemic effects and to ensure the patch will remain in place (DH 2007, C; Snyder 2007, E).

6 Remove any drug residue from the former site before placing the next patch. To avoid any skin irritation (Chernecky et al. 2002, E).

7 Carefully remove