Herpes zoster

Management Strategy

Early treatment – within the first 72 hours of vesicle formation – is important for antiviral efficacy, time to lesion healing, and minimizing zoster-associated pain (although initiating treatment after 72 hours may still be effective). Aciclovir , valaciclovir , and famciclovir are guanosine analogs that are phosphorylated by thymidine kinase to a triphosphate form that inhibits viral deoxyribonucleic acid (DNA) polymerase. The oral bioavailability of the antivirals determines the number of daily administrations. Patient compliance tends to decrease as the number of daily administrations increases. The most common side effects seen are headache and gastrointestinal upset, but these drugs are otherwise safe and well tolerated. Patients with renal insufficiency will need an adjusted dose, as these medications are excreted by the kidneys.

Aciclovir-resistant VZV infections have been reported in immunocompromised patients (i.e., acquired immune deficiency syndrome [AIDS], transplant patients), and in these cases foscarnet (given intravenously 40 mg/kg three times daily) can be used as an alternative.

Acutely, corticosteroids may reduce zoster-associated pain, but they are associated with a risk of serious adverse events and have shown no benefit in reducing time to complete cessation of pain or prevention of PHN.

Pain management is especially difficult with conventional analgesics in zoster patients who develop PHN. Calcium channel α2-δ ligands (gabapentin and pregabalin), tricyclic antidepressants, opioids, topical lidocaine ( Table 105.1 ), selective serotonin and norepinephrine reuptake inhibitors (duloxetine and venlafaxine), and topical capsaicin have been shown to reduce the pain associated with PHN. Of these medications, only gabapentin, pregabalin, 5% lidocaine patch, and 8% capsaicin patch have been approved by the Food and Drug Administration (FDA) specifically for the treatment of PHN. Adding gabapentin to an antiviral in patients with acute herpes zoster appears to significantly reduce the incidence of PHN. In January 2011, the FDA approved Gralise as a once-daily medication for the treatment of postherpetic neuralgia. Gralise is an extended-release form of gabapentin that not only has been shown to significantly decrease PHN pain scores but may also be associated with fewer side effects than its immediate-release counterpart. In 2012 the FDA approved Horizant, gabapentin enacarbil, for the once-daily therapy of PHN.

Vaccination of patients aged 50 years and over is the most promising option for preventing herpes zoster and, therefore, PHN. As of February 2020, there are two types of FDA-approved zoster vaccines. The first is Zostavax, a live attenuated varicella vaccine approved in 2006. The second is Shingrix, a recombinant zoster vaccine approved in 2017, which is the current recommended vaccine. Studies in adults aged 50 and older showed that five randomized controlled trials compared the live attenuated vaccine with the adjuvant recombinant subunit vaccine and placebo. Shingrix demonstrated a vaccine efficacy superior to both Zostavax and placebo (85% and 94%, respectively). In a clinical trial involving over 15,000 adults aged 50 or older, Shingrix reduced the risk of herpes zoster by 97.2%. However, there is an increased risk of injection site reactions with Shingrix compared with Zostavax. The Advisory Committee on Immunization Practices recommends two doses of Shingrix administered within 2–6 months for immunocompetent adults aged 50 years or older.