Topical analgesics are often used to treat the debilitating pain of postherpetic neuralgia (PHN) in patients who have experienced shingles (herpes zoster). PHN results from damage to a peripheral nerve that causes neuropathic pain that persists for more than 90 days after an outbreak of shingles.
A transdermal patch is a convenient local anesthetic delivery system. In the United States, two very different patches are approved by the FDA for treatment of PHN.
The efficacy of Lidoderm (lidocaine 5%) in PHN cases has been established for more than two decades. Logistically, it is the easiest patch to administer and can be applied by the patient at home without medical supervision.
“Lidocaine is actually a numbing medication,” says David Simpson, M.D., professor of neurology and director of the Neuromuscular Disease Division at the Icahn School of Medicine at Mount Sinai in New York. “By its label, the lidocaine patch is indicated to be put 12 hours on the skin and removed for 12 hours. It works only when it’s on the skin, delivering lidocaine to the area of skin to which it’s applied.”
During or immediately following treatment with Lidoderm, the skin at the site of application may develop blisters, bruising, a burning sensation, depigmentation, dermatitis, edema, or other irritations or reactions. These reactions are generally mild and transient, resolving within hours.
The second option is the 8% capsaicin transdermal patch marketed in the United States as Qutenza. Capsaicin, an active component of chili peppers, is an irritant that produces a burning sensation when it comes in contact with human tissue.
A capsaicin review, conducted in the United Kingdom and published in 2016, notes that the patch is applied after a PHN patient’s skin has been pretreated with a local anesthetic or an oral analgesic.
“The Qutenza patch is applied in the clinic under a doctor’s supervision. Depending on the part of the body where it’s applied, it’s applied for between 30 to 60 minutes and then removed,” Simpson explains. “The capsaicin can actually burn when it’s applied, and therefore we sometimes use pain medication during the procedure to minimize the pain of the burn.” Once the capsaicin treatment is over, the pain relief can last up to three months.
Topical capsaicin stimulates receptors in the skin and desensitizes sensory neurons to inhibit pain transmission. The U.K. review concluded that capsaicin 8% patches appear to be safe and effective in treating PHN, although not without side effects like redness, pain, itching, small bumps where the patch was applied, and nausea.
A controlled study of a third potential option—a transdermal oxycodone patch containing tocopheryl phosphate mixture (TPM)—was published in 2017. It noted that the patch delivered a low systemic exposure to oxycodone and was well tolerated.
While the oxycodone patch did not significantly improve average Numeric Pain Rating Scale scores, PHN patients with high levels of paresthesia experienced improved pain reduction. The researchers concluded, however, that the patch did not provide analgesia for the broad PHN indication.