Pharmacology Update

Lidocaine Patch 5% (Lidoderm—Endo Pharmaceuticals)

By William T. Elliott, MD, FACP, and James Chan, PharmD, PhD

Recently, the fda approved endo pharmaceutical’s Lidoderm, the first product ever approved for the relief of pain associated with postherpetic neuralgia (PHN). The product consists of lidocaine, formulated as an adhesive patch for local anesthetic activity. When applied to the skin, the topical lidocaine causes local analgesia, relieving the symptoms of PHN, a complication of herpes zoster or shingles, and one of the most difficult clinical entities to treat. Lidoderm is manufactured by Teikodu Seiyaku Co. in Japan and marketed by Endo Pharmaceuticals.

Indications

Lidocaine patch is indicated for the relief of pain associated with PHN.

Dosage

Lidocaine patch should be applied to intact skin covering the most painful area. Up to three patches may be applied, but only for up to 12 hours within a 24-hour period. Patches may be cut into smaller sizes. Application on broken or inflamed skin is not recommended.1

Potential Advantages

Lidocaine patch provides a nonsystemic, easy-to-use formulation to reduce the pain intensity of PHN. Lidocaine patch has been reported to show statistical evidence of efficacy over placebo patch in reducing pain intensity from four to 12 hours of application.2 The patch may also provide some protection from mechanical stimulation, such as clothing or inadvertent touching. While there was some evidence that the patch reduced allodynia, this end point was not an efficacy variable in the study protocol and the results are considered exploratory by the FDA.

Potential Disadvantages

Application of more than three patches (420 cm2) and duration greater than 12 hours should be avoided since the amount of lidocaine absorbed systemically, and the potential for systemic side effects, is dependent on the surface area covered and the duration of skin contact. Local cutaneous reactions have been reported with the patch, including erythema, edema, or locus of abnormal sensations. These reactions are generally mild and transient.

Comments

It appears that lidocaine patch was approved based on very limited data. The active patch was compared to a vehicle patch and no treatment in a single-dose trial involving 35 subjects. These subjects were elderly (mean age, 75 years) and had established PHN affecting the torso or extremities.2 Patients were permitted to use oral medication commonly used in the treatment of PHN, including analgesic as needed ,1 but they were not allowed to start new oral medications. Only constant pain was evaluated—not pain induced by sensory stimuli (dysesthesia). Pain relief was modest, as 40% of patients reported slight to moderate pain relief, 28.5% slight or no relief, 20% had moderate to lots of relief, 8.6% had complete relief, and 2.9% reported worst or no relief. This also corresponded to about a 12% decrease in the least-square mean pain intensity based on a visual analog scale. Even with a large placebo effect with the vehicle patch (vs no treatment), there was a statistically significant difference in favor of lidocaine patch from four to 12 hours after application. Subjects were able to peel off the patches with only minor and transient increase in pain. It is difficult to assess the efficacy of the patch alone as the study protocol permitted concurrent use of oral analgesics.

Lidocaine patch is expected to be available in mid-September. Price information was not available at the time of this writing.

Clinical Implications

The incidence of herpes zoster is estimated to be 600,000-1 million cases per year. It is caused by the same virus that causes childhood chickenpox, varicella-zoster. PHN is one of the major complications of herpes zoster (shingles), affecting up to 200,000 Americans. This condition is particularly problematic for the elderly. At the age of 60 years, there is about a 50% chance of significant pain persisting one month or longer after the onset of herpes zoster skin lesions.4 This compares to 10% for the population as a whole. Pain is often severe in areas where the blisters occurred. The area is also highly sensitive to touch, heat, and cold. Prompt treatment of herpes zoster with antiviral drugs such as famciclovir may decrease the duration of PHN.3 PHN has traditionally been treated with analgesics (narcotic and non-narcotic), antidepressants, anticonvulsants (e.g., gabapentin), capsaicin, and transcutaneous electrical stimulation. The efficacy of lidocaine patch, while modest, does provide another option for the management of a difficult clinical entity.

References

1. Lidoderm Product Information. Endo Laboratories. March 1999.

2. Rowbotham MC, et al. Pain 1996;65(1):39-44.

3. CDC. http:/www.cdc.gov/ncidod/srp/varicella.htm

4. Watson CPN. Neurology 1995;45(suppl 8):S58-S60.

Which is not true about the lidocaine patch (Lidoderm)?

a. It can be applied on top of the zoster vesicles.

b. It should be used only for 12 out of 24 hours.

c. It may be cut to size.

d. There are no systemic effects of the patch.