Treating herpes zoster and postherpetic neuralgia: An evidence-based approach

Opioid analgesics are recommended as second- and third-line agents for PHN. Adverse effects include nausea, pruritus, sedation, confusion, constipation, hypogonadism, and risk of developing tolerance and abuse.

A double-blind crossover trial evaluated the analgesic efficacy of oral oxycodone; treatment resulted in significant reduction of allodynia, steady pain, and spontaneous paroxysmal pain. Oxycodone treatment resulted in superior scores of global effectiveness, disability reduction, and patient preference, compared with placebo.²⁷

In a randomized crossover trial, the combination of gabapentin and morphine was superior to either of these medications alone in relieving pain in PHN.²⁸

Tramadol, an atypical opioid, has a weak μ-opioid receptor agonist effect and inhibits reuptake of serotonin and norepinephrine. Avoid using it in patients with a history of seizures. The maximum recommended dosage is 400 mg/d. An extended-release formulation of tramadol is also available.

Tramadol provided superior pain relief and improved quality of life in PHN patients in a randomized placebo-controlled trial.²⁹

Tapentadol has weak μ-opioid receptor agonist activity; norepinephrine reuptake inhibition is more predominant than serotonin reuptake inhibition. This drug is also available as an extended-release formulation. The maximum recommended dosage is 600 mg/d.

Avoid using tapentadol in patients with a history of seizures. Note: Although there is no scientific evidence regarding the use of tapentadol in neuropathic pain, we use it often in our practice.

Topical therapies

Treating PHN with a topical agent is associated with relatively fewer adverse effects than what has been seen with oral therapy because systemic absorption is minimal.

Lidocaine is available as a transdermal patch and as a topical gel ointment. The 5% lidocaine patch is FDA approved for treating PHN. Lidocaine, a sodium-channel blocker, is useful for treating patients with clinical evidence of allodynia. You can cut a patch to fit the affected area; a maximum of 3 patches can be used simultaneously for 12 hours on, 12 hours off. If helpful, the patch can be left in place for 18 hours.³⁰

In 2 open-labeled, nonrandomized prospective studies, patients treated with the lidocaine patch had reduced intensity of pain and improved quality of life.^31,32

If lidocaine patches are not available, or affordable, or if a patient has difficulty applying them, use 5% lidocaine gel instead.

Capsaicin topical cream is sold in 2 concentrations: 0.025% and 0.075%. An extract of hot chili peppers, capsaicin acts as an agonist at the vanilloid receptors. The recommended dosage is 3 or 4 times a day. Initial application causes burning to become worse, but repeated use results in diminished pain and hyperalgesia.

A 6-week, blinded parallel study, followed by a 2-year open label follow-up, showed that the 0.075% dose of topical capsaicin cream relieved pain in 64% of patients; pain was relieved in 25% of placebo-treated patients.³³

An 8% capsaicin patch is FDA approved for treating PHN. The patch must be applied by a health care professional in a monitored setting. Prepare the affected area by pretreating it with a local anesthetic cream; then apply the patch and leave it in place for 1 hour. As many as 4 patches can be used at once. A single application can provide pain relief for as long as 12 weeks. Adverse effects are mostly mild and transient.

In a double-blind, randomized, placebo-controlled trial with an open-label extension, the score on a numeric pain-rating scale declined from baseline in both the high-concentration capsaicin group and the placebo group during Week 1; however, the capsaicin-treated group experienced long-term improvement through Week 12.³⁴

(See TABLE 1^{14-21, 23, 24, 27-34} for a summary of pharmacotherapeutic options.)

TABLE 1

Pharmacotherapeutic options for managing postherpetic neuralgia^{14-21, 23, 24, 27-34}