Repartos de beneficios (Dividendos)

Neuralgia

Herpes zoster (shingles) results from reactivation of the varicella-zoster virus. Herpes zoster has a lifetime incidence of 10 to 20 percent. The incidence of herpes zoster increases sharply with advancing age, doubling in each decade past the age of 50 years.

I. Clinical evaluation

A. Herpes zoster typically presents with a prodrome

consisting of hyperesthesia, paresthesias, burning dysesthesias or pruritus along the affected dermatome(s). The prodrome generally lasts one to two days.

B. The prodromal phase is followed by development

of a maculopapular rash that follows a dermatomal distribution. The maculopapular rash evolves into vesicles with an erythematous base. The vesicles are painful, and their development is often associ- ated with flu-like symptoms.

C. Although any vertebral dermatome may be in-

volved, T5 and T6 are most commonly affected. The most frequently involved cranial nerve dermatome is the ophthalmic division of the trigeminal nerve.

D. The most common chronic complication of herpes

zoster is postherpetic neuralgia. Pain that persists for longer than one to three months after resolution of the rash is a sign of postherpetic neuralgia. Affected patients usually report constant burning, lancinating pain. Symptoms tend to abate over time. Less than one-quarter of patients still experi- ence pain at six months after the herpes zoster eruption, and fewer than one in 20 has pain at one year.

II. Treatment of herpes zoster A. Antiviral agents

1. Antiviral agents have been shown to decrease

the duration of herpes zoster rash and the severity of pain in patients who receive antiviral agents within 72 hours after the onset of rash.

2. Acyclovir (Zovirax), valacyclovir (Valtrex) and

famciclovir (Famvir) therapy appear to produce a moderate reduction in the development of postherpetic neuralgia. Major drawbacks of orally administered acyclovir include its lower bioavailability compared with other agents and its dosing frequency (five times daily).

3. Valacyclovir (Valtrex) is administered three

times daily. Compared with acyclovir, valacyclovir may be slightly better at decreasing the severity of pain and the duration of postherpetic neuralgia.

4. Famciclovir (Famvir). The advantages of

famciclovir are its dosing schedule (three times daily), its longer intracellular half-life compared with acyclovir and its better bioavailability com- pared with acyclovir and valacyclovir.

Treatment Options for Herpes Zoster

Medication Dosage

Acyclovir (Zovirax)

800 mg orally five times daily for 7 to 10 days

10 mg per kg IV every 8 hours for 7 to 10 days

Famciclovir

(Famvir) 500 mg orally three times daily for 7days Valacyclovir

(Valtrex) 1,000 mg orally three times daily for 7days Prednisone

(Deltasone)

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 2 (2 to 4) for days 1 through 7

2 (1 to 3) for days 8 through 14 1 (1 to 2) for days 15 to 21

B. Corticosteroids. Prednisone used in conjunction

with acyclovir has been shown to reduce the pain associated with herpes zoster. Prednisone may decrease the incidence of postherpetic neuralgia. It should be used only in patients more than 50 years of age because they are at greater risk of develop- ing postherpetic neuralgia.

C. Analgesics. Mild to moderate pain may respond to

over-the-counter analgesics. More severe pain may require a narcotic. Lotions containing calamine (eg, Caladryl) may be used on open lesions to reduce pain and pruritus. Once the lesions have crusted over, capsaicin cream (Zostrix) may be applied. Topical lidocaine (Xylocaine) and nerve blocks have also been reported to be effective in reducing pain.

D. Ocular involvement. Ocular herpes zoster is

treated with oral antiviral agents and corticosteroids. Ophthalmologic consultation is recommended.

III. Treatment of postherpetic neuralgia

A. Although postherpetic neuralgia is generally a

self-limited condition, it can last indefinitely.

Treatment Options for Postherpetic Neuralgia

Medication Dosage

Topical agents

Capsaicin cream

(Zostrix) Apply to affected area three to fivetimes daily. Lidocaine

(Xylocaine) patch

Apply to affected area every 4 to 12 hours as needed.

Tricyclic antidepressants

Amitriptyline (Elavil)

0 to 25 mg orally at bedtime; increase dosage by 25 mg every 2 to 4 weeks until response is adequate, or to maxi- mum dosage of 150 mg per day. Nortriptyline

(Pamelor) 0 to 25 mg orally at bedtime; increasedosage by 25 mg every 2 to 4 weeks until response is adequate, or to maxi- mum dosage of 125 mg per day. Imipramine

(Tofranil) 25 mg orally at bedtime; increase dos-age by 25 mg every 2 to 4 weeks until response is adequate, or to maximum dosage of 150 mg per day. Desipramine

(Norpramin) 25 mg orally at bedtime; increase dos-age by 25 mg every 2 to 4 weeks until response is adequate, or to maximum dosage of 150 mg per day.

Anticonvulsants

Phenytoin (Di- lantin)

100 to 300 mg orally at bedtime; in- crease dosage until response is ade- quate or blood drug level is 10 to 20 :g per mL (40 to 80 :mol per L). Carbamazepine

(Tegretol) 100 mg orally at bedtime; increase dos-age by 100 mg every 3 days until dos- age is 200 mg three times daily, re- sponse is adequate or blood drug level is 6 to12 :g per mL (25.4 to 50.8 :mol per L).

Gabapentin (Neurontin)

100 to 300 mg orally at bedtime; in- crease dosage by 100 to 300 mg every 3 days until dosage is 300 to 900 mg three times daily or response is ade- quate.

B. Analgesics

1. Capsaicin is more efficacious than placebo but

must be applied to the affected area three to five times daily. Pain will likely increase during the first few days to a week after capsaicin therapy is initiated.

2. Lidocaine patches reduce pain intensity, with

minimal systemic absorption. The effect lasts only four to 12 hours with each application.

3. A c e t a m i n o p h e n a n d n o n s t e r o i d a l

anti-inflammatory drugs are useful for potentiat- ing the pain-relieving effects of narcotics.

C. Tricyclic Antidepressants

1. Tricyclic antidepressants can be effective ad-

juncts in reducing pain. Tricyclic antidepressants commonly used in the treatment of postherpetic neuralgia include amitriptyline (Elavil), nortriptyline (Pamelor), imipramine (Tofranil) and desipramine (Norpramin).

2. The tricyclic antidepressants may cause seda-

tion, dry mouth, postural hypotension, blurred vision and urinary retention. Nortriptyline is better tolerated.

D. Gabapentin is effective in treating the pain of

postherpetic neuralgia. The dosages required for analgesia are often lower than those used in the treatment of epilepsy.

E. Transcutaneous electric nerve stimulation

(TENS), biofeedback and nerve blocks are also sometimes used.