Herpes zoster virus infection and treatment.👿👿👿

Herpes zoster is an infectious skin disease caused by the varicella-zoster virus that is latent in the human body and then activated. It is a clinically common viral skin disease. This article will introduce the knowledge about the pathology, prevention and treatment of herpes zoster.

How can you get herpes zoster?

Varicella-zoster virus causes chickenpox in people who are first infected. When a chickenpox patient is cured, the virus is not completely cleared from his body. The rest of the virus lurks in the ganglia along the sensory nerves. When his immunity declines, these latent viruses reactivate. The viruses do a lot of replication, and then they spread along the sensory nerve fibers to the areas of the skin that these nerves control. It can cause herpes zoster. When the body's immunity is good, although herpes zoster will not be caused, the virus can remain dormant in the ganglia waiting to be activated. 

What kind of disease is herpes zoster?

The varicella-zoster virus is a DNA-like virus. It is characterized by being close to the skin and close to the nerves. It always spreads along the nerve and is distributed in strips. It generally occurs only on one side of the patient's body and does not go beyond the midline. Herpes zoster consists of dense clusters of blisters. Its course is usually 2 to 4 weeks. Postherpetic neuralgia is a common complication of herpes zoster. This can last for months or even years. The older the patient, the more severe the symptoms of neuralgia. In addition, the risk of developing herpes zoster is greater for women than for men.

What is the treatment for herpes zoster?

Goals of treatment: Relief of acute pain in patients, limitation of spread of skin lesions, promotion of repair of skin lesions, prevention or alleviation of postherpetic neuralgia.

Medications for herpes zoster:

Antiviral: It can promote the healing of herpes, effectively shorten the course of the disease, reduce the formation of new herpes and prevent the spread of the virus to the internal organs. Antiviral medication should be started within 24 to 72 hours of the blisters. This allows the drug to reach the effective concentration quickly and obtain the best therapeutic effect. Commonly used drugs are as follows:

• Acyclovir: It is indicated for patients with severe and immunocompromised herpes. The usual dose is 5 to 10 mg intravenously per kg, 3 times a day for 7 consecutive days. Crystals may form in the kidneys at high doses. Therefore, patients should drink plenty of water during the medication. In addition, it is neurotoxic. Clinical manifestations include epileptic seizure, paresthesia and neurological confusion.
• Valacyclovir: It is a precursor to acyclovir. The same applies to patients with severe and immunocompromised herpes. Its bioavailability is 3 to 5 times that of acyclovir. The usual dose is 0.3g orally three times a day for 7 consecutive days. Also crystals may form in the kidneys at high doses. Patients should drink plenty of fluids during the medication. It is also neurotoxic. Clinical manifestations include epileptic seizure, paresthesia and neurological confusion.
• Famciclovir: It is present in higher concentrations in infected cells and has a longer half-life. Its efficacy is similar to that of valacyclovir. The usual dose is 0.25g 3 times a day for 7 consecutive days. Its common side effects are headache, nausea and diarrhea. It can also cause hives, hallucinations and confusion, especially in the elderly.
• Foscarnet: It is indicated for patients with herpes who are resistant to nucleoside analogs. The usual dose is 100 mg intravenously per kg, twice a day. It is nephrotoxic and neurotoxic. Serum creatinine is elevated in more than half of patients and headache in about 25%. In addition, it has the side effects of hypocalcemia, hypokalemia, and hypomagnesemia.

Analgesics: Calcium channel modulators (eg, gabapentin or pregabalin) and tricyclic antidepressants (eg, amitriptyline) are first-line therapy. Opioids and tramadol are second-line treatments. Aspirin and acetaminophen have limited effects. 

• Gabapentin: It is a 1st generation calcium channel blocker. Its pharmacokinetic profile is nonlinear. The starting dose is 300 mg orally per day, and the usual effective dose is 900 to 1800 mg per day. Common side effects include drowsiness, dizziness, blurred vision, edema, dry mouth, weight gain, and abnormal thinking.
• Pregabalin: It is a second generation calcium channel blocker. Hyperalgesia and central sensitization will be inhibited by it to achieve analgesic effect. The starting dose is 150 mg orally per day, which can be increased to 300 mg per day within 1 week, with a maximum dose of 600 mg per day. Common side effects are the same as gabapentin.
• Amitriptyline: It inhibits the reuptake of norepinephrine and serotonin and blocks various ion channels. The descending pathway of pain conduction is where it primarily works. The starting dose is 25 mg orally per day and the maximum dose is 150 mg per day. Common side effects include blurred vision, dizziness, tremor, drowsiness, sweating, dry mouth, constipation, dysuria, and orthostatic hypotension.

Anti-inflammatory drugs: Oral corticosteroids can suppress the inflammatory process in the early stages of an acute herpes zoster attack. It reduces the healing time of skin lesions and the duration of acute pain. However, it has no effect on postherpetic neuralgia that has already occurred. In addition, patients should not use topical corticosteroids. It does not recommend the use of glucocorticoids alone in the absence of systemic antiviral therapy.

• Prednisone: Start with a daily dose of 30 to 40 mg and then gradually reduce the dose. Its course of treatment is 1 to 2 weeks.

Neurotrophic: It is helpful for nerve pain and link neuroinflammation, but its therapeutic effect is limited. Commonly used drugs are vitamin B1, methylcobalamin and vitamin B12, which can be injected intramuscularly or orally.

Topical medicines: Its main purpose is to reduce inflammation and dryness.

• Acyclovir cream, penciclovir cream and calamine lotion: These can be used topically when the herpes is not broken.
• 3% boric acid solution or 1:5000 nitrofurazone solution (wet compress), 2% mupirocin ointment and 0.5% neomycin ointment: After the herpes has ruptured, these drugs may be used as appropriate.
• 5% lidocaine patch: It can be used for postherpetic pain. Place 1 to 3 patches on the painful area, each patch for up to 12 hours.

How to prevent herpes zoster?

The herpes zoster vaccine is effective in preventing the occurrence of herpes zoster, shortening its duration, and reducing the incidence of postherpetic neuralgia. Generally, herpes zoster recurs only once in a lifetime. However, very few patients can relapse several times. Adults ≥50 years of age should get the herpes zoster vaccine even if they have ever had herpes zoster.