Prevention and Treatment of Herpes Zoster and Postherpetic Neuralgia
Prevention and Treatment of Herpes Zoster and Postherpetic Neuralgia
Lamis Ibrahim
James W. Myers
INTRODUCTION
Varicella-zoster virus (VZV) causes chicken pox as primary infection, and then it resides in sensory ganglia in latent stage. Reactivation of the latent virus causes zoster infection especially when VZV cell-mediated immunity declines.
Herpes zoster (HZ) presents with vesicular, painful rash that follows a dermatomal distribution and usually lasts 1 week to 10 days.
Thoracic dermatomes are most commonly affected.
It can be transmitted through direct contact with skin lesions till they epithelize or through airborne transmission if disseminated infection is present
In immunocompromised patients, it can cause disseminated skin infection and may involve other organs especially the nervous system.
A significant complication of zoster is pain. Pain is divided into three stages: acute pain (occurs within 30 days of onset of rash), subacute pain (occurs within 30 to 120 days of rash), and postherpetic neuralgia (PHN) which is persistent pain beyond 120 days after zoster rash onset.
PHN
May persist for months or years.
It can be extremely incapacitating and can result in insomnia, weight loss, and an inability to perform daily tasks of living.
Its effect on quality of life may be similar to that of other chronic diseases like diabetes, depression, and congestive heart failure.
Pathophysiology is not very well understood.
Pathologic studies have demonstrated damage to the sensory nerves, the sensory dorsal root ganglia, and the dorsal horns of the spinal cord in patients with this condition.
The pain of HZ results from a sequence of changes in neuronal sensitivity starting at the point of neural damage in the periphery and moving centrally to affect one cell after another within the pain pathway.
Once central sensitization occurs, attempts to reduce the pain purely by influencing peripheral nociceptor function are unlikely to be successful.
Furthermore, once established, such neuropathic pain is notoriously difficult to control.
Risk factors include old age, severity of acute pain, female sex, and possibly ophthalmic distribution.
Table 19-1 Antiviral Therapy of Zoster
Medication
Dose
ACV
800 mg orally five times daily for 7-10 days
10 mg/kg IV every 8 hours for 7-10 days
500 mg orally three times daily for 7 days
Antiviral therapy has been shown to be beneficial only when patients are treated within 72 hours of onset of the HZ rash
Famciclovir Valacyclovir
1,000 mg orally three times daily for 7 days
Prednisone
30 mg orally twice daily on days 1 through 7; then 15 mg twice daily on days 8 through 14; then 7.5 mg twice daily on days 15 through 21
Prednisone used in conjunction with ACV has been shown to reduce the pain associated with HZ but probably is ineffective for PHN. Probably more useful for those patients older than age 50
Is structurally related to the neurotransmitter GABA (gamma-aminobutyric acid). The mechanism by which gabapentin exerts its analgesic action is unknown.
It is demonstrated to provide significant benefits when compared with placebo.
Studies showed that treatment with gabapentin at daily doses of 1,800 to 3,600 mg was associated with a statistically significant reduction in daily pain ratings as well as improvements in sleep, mood, and quality of life.
It may cause dizziness, somnolence, and other symptoms and signs of CNS depression and can cause or exacerbate gait and balance problems and cognitive impairment in elderly patients
To reduce side effects and increase patient compliance with treatment, gabapentin should be initiated at low dosages and then titrated, as tolerated.
Dosing information can also be found on the Internet at www.rxlist.com/cgi/generic/gabapent.htm
Lyrica (pregabalin):
Is a modulator of voltage-gated calcium channels, designed to affect neurologic transmission.
For the treatment of PHN, recommended initial dosing is 75 mg twice daily or 50 mg thrice daily (in patients with creatinine clearance>60 mL/min), with escalation to 150 mg twice daily or 100 mg thrice daily (in patients with creatinine clearance>60 mL/min) permissible.
Table 19-2 Treatment Options for PHN
Medication
Dosage
Topical Agents
Capsaicin cream (Zostrix)
Apply to affected area three to five times daily
Lidocaine (Xylocaine) patch
Apply to affected area every 4-12 hours as needed (http://www.endo.com/PDF/lidoderm_pack_insert.pdf)
Tricyclic Antidepressants
Amitriptyline (Elavil)
25 mg orally at bedtime; increase dosage by 25 mg every 2-4 weeks until response is adequate, or to maximum dosage of 150 mg/day
Nortriptyline (Pamelor)
25 mg orally at bedtime; increase dosage by 25 mg every 2-4 weeks until response is adequate, or to maximum dosage of 125 mg/day
Desipramine (Norpramin)
25 mg orally at bedtime; increase dosage by 25 mg every 2-4 weeks until response is adequate, or to maximum dosage of 150 mg/day
Anticonvulsants
Gabapentin (Neurontin)
100-300 mg orally at bedtime; increase dosage by 100-300 mg every 3 days until dosage is 300-900 mg three times daily or response is adequate
Lyrica
Start with 75 mg b.i.d. and titrate dose.
Adapted from Stankus SJ, et al. Management of herpes zoster (shingles) and postherpetic neuralgia. Am Fam Physician 2000;61:2437-2444, 2447-2448.
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