Herpes zoster--also known as varicella-zoster virus, or shingles--is a disease caused by the reactivation of the same virus that causes chicken pox. After a person has been infected by chicken pox, generally in childhood, the virus remains dormant in the central nervous system. When a person's immune system becomes weakened due to stress, aging or conditions such as cancer, AIDS or diabetes, the virus proceeds down the nerve endings and causes pain and lesions.
Acyclovir
Acyclovir prevents DNA synthesis of the herpes zoster virus. This prevents the virus from reproducing. Acyclovir does this by two different functions. It blocks the action of an enzyme in the virus and incorporates itself into the DNA of the virus. The dose required for herpes zoster is 800mg, five times a day. The most common side effects are agitation, anemia and confusion.
Valacyclovir
Valacyclovir is a prodrug of acyclovir. This means that the body converts it to acyclovir once it enters the system. This enables the drug to stay active in the body for a longer period, so you don't need to take it as frequently. The dose of valacyclovir in herpes zoster is 1,000mg every eight hours.
Famciclovir
Famciclovir is in the same class of drugs as acyclovir. It doesn't block the enzyme needed for viral reproduction quite as strongly as acyclovir, but because it's a longer-acting drug that reaches higher concentrations in the cells, it's comparatively effective. The recommended dosage for famciclovir in herpes zoster is 500mg three times daily for seven days.
Foscarnet
Foscarnet blocks the action of several different enzymes needed for viruses to reproduce. This makes it effective against many other viruses, such as HIV and cytomegalovirus. Foscarnet is not absorbed well when taken by mouth, so it must be given intravenously. It's used against shingles infections that are resistant to other drugs. The dosage in herpes zoster is 40mg of drug for each kilogram of body weight given by IV every eight hours until healed.
Corticosteroids
Corticosteroids, or steroids, are drugs that reduce inflammation. When used in herpes zoster, they can reduce inflammation in the nerves and decrease the amount of long-term nerve damage. Prednisone is the most commonly used steroid in shingles. The dose varies, but patients usually begin with 30mg three times daily and gradually reduce the dose over three weeks.
Pain Medications
Pain medications don't heal herpes zoster, but they make you more comfortable. Topical drugs such as capsaicin and lidocaine, tricyclic antidepressants such as amitriptyline, and anticonvulsants such as phenytoin and pregabalin are all used for pain from shingles. Narcotics including codeine and morphine are sometimes given as a last resort to patients with severe pain that's not relieved by other medications.
References
- Basic and Clinical Pharmacology; Bertram Katzung; 2007
- U.S. Pharmacist: Herpes Zoster (Shingles) and Postherpetic Neuralgia Management
