When KC, 71, came to the provider's office for her annual physical, she reported feeling a burning, tingling pain on her back ever since she was treated for shingles approximately 5 months earlier. She does not want to add another oral medication to her current regimen to manage the pain. Are transdermal patches an option for managing this type of pain?-C.L., KAN.
Janessa Cohrs, BSPS, and Rachel Kerns, PharmD, RPh, reply: Yes. Although acute herpes zoster (shingles) is generally self-limiting, some patients continue to experience pain for months or even years after the rash resolves, a condition known as postherpetic neuralgia (PHN).1 Lidocaine or capsaicin formulated in a transdermal delivery system (patch) may be good alternative to oral pain medication for patients like KC who are experiencing PHN.
A transdermal delivery system has many advantages, including easy application directly to the painful site, consistent medication delivery, and convenience. Besides reducing the need for oral or injectable medications, topical patches are less likely to cause adverse reactions and drug interactions because drugs administered transdermally evade initial drug metabolism in the gastrointestinal tract and liver.2,3
Currently, evidence supports the use of topical lidocaine and capsaicin for relief of PHN.4 Treatment algorithms for neuropathic pain list topical products as first-line options, especially if the pain is localized.4,5
Topical products for neuropathy include lidocaine creams, roll-on gels, and patches; and capsaicin cream and patches. The focus of this discussion is the use of lidocaine and capsaicin transdermal patches to treat localized neuropathic pain.
Lidocaine: Local hero
Lidocaine stops the initiation and conduction of neuropathic pain signals by limiting the cell membrane's permeability to sodium ions, which prevents neuron depolarization.6 Through this mechanism, lidocaine quickly dulls the sharp burning, shooting sensations characteristic of neuropathic pain.
Topical lidocaine patches are available as both over-the-counter (OTC) and prescription-strength products. OTC products typically contain 4% lidocaine and may also contain menthol or methyl salicylate, which contribute a cooling pain relief.
In the US, a 5% lidocaine patch is available by prescription.7 Another patch containing 1.8% lidocaine is also available by prescription.8 Although the percentage of lidocaine is lower in this product, it provides lidocaine exposure equivalent to the 5% patch due to a different adhesive system.
Teach patients to use only one lidocaine patch at a time and, unless otherwise directed by the healthcare provider (HCP), to wear it for only 12 hours a day because the risk of adverse reactions and toxicity increases as lidocaine accumulates in the body. Patients should not continue using lidocaine patches for more than a week without consulting the HCP.
One study found that lidocaine toxicity usually begins when serum concentrations are around 6 mcg/mL, with serious cardiac adverse reactions occurring at plasma concentrations greater than 10 mcg/mL.2,9 However, some individuals may have a lower threshold for toxicity; for example, those who have had other recent exposure to anesthetic agents and those with hepatic or renal dysfunction, a history of anesthetic toxicity, or cardiac or neurologic disorders.9 Nurses must teach patients to recognize signs and symptoms of local anesthetic toxicity: headache, confusion, blurry vision, and tinnitus. Signs of central nervous system excitability, such as agitation and muscle twitching, may advance to signs of central nervous system depression, such as drowsiness and slurred speech.10,11 Severe signs and symptoms, such as seizures and difficulty breathing, are medical emergencies that require immediate treatment.
Capsaicin: Feel the burn
Capsaicin is the "spicy" ingredient of chili peppers. The burning sensation and erythema that may occur with application also help reduce nerve pain sensation. By depleting substance P in neurons, capsaicin mediates pain impulses from the periphery to the central nervous system, impeding pain signal transmission.12
Applying a thin layer of a topical anesthetic (such as lidocaine) to the skin before applying a capsaicin patch can reduce the unpleasant burning sensation associated with capsaicin. Despite this adverse reaction, studies show that over 50% of people are still willing to try another application 90 days later.13,14
As an OTC product, capsaicin is available in creams, ointments, and patches at low concentrations. These products can be applied three to four times each day for several days or weeks for effective pain relief.1
Available by prescription only, a capsaicin 8% patch is applied by an HCP and removed after 60 minutes.15 The treatment can be repeated every 90 days if indicated. Providers must wear nitrile (not latex) gloves when handling the patch and cleansing the treatment area after patch removal. Studies show that the capsaicin 8% patch provides neuropathic pain relief just as effectively as some oral prescription medications, with a faster onset of pain relief.13,16,17
Nursing considerations
Educate patients using transdermal pain patches about the following:18,19
* Apply patches to a clean, dry area of the skin. Do not apply patches to broken or irritated skin.
* If a patch causes irritation or skin damage, stop using topical patches and consult the HCP.
* Do not use heating pads or any other external heat source over the area where the patch is applied. Heat can increase absorption, increasing the risk of toxicity. Heat can also cause pain and erythema at the patch application site.
* Because of their small size, children are especially susceptible to anesthetic toxicity from accidental exposure to transdermal patches. Even after removal, transdermal patches contain some active medication. Used patches should be carefully disposed of by folding in half and discarding in the household trash.20 Like all medications, patches must be stored and disposed of out of the reach of children and pets.
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