Valacyclovir (Valtrex®) for Shingles
Valacyclovir hydrochloride (Valtrex) is indicated for the treatment of herpes zoster (shingles); initial and recurrent episodes of genital herpes; suppression of recurrent genital herpes; cold sores. It is also DFA approved for the reduction of transmission of genital herpes to the uninfected partner.
Valacyclovir does not cure a herpes infection but may relieve the symptoms of viral infection and shorten the duration of an outbreak.
Herpes zoster (also called shingles) is a painful, blistering skin rash. Thoracic and lumbar areas of the body are most commonly affected. Shingles results from reactivation of the varicella-zoster virus acquired during the primary varicella infection, or chickenpox. Whereas chickenpox happens generally during childhood, the incidence of shingles increases sharply with advancing age. The main complication of shingles is postherpetic neuralgia (PHN), the pain persisting weeks to months after the rash has healed.
Treatment of herpes zoster has three main goals: treatment of herpes zoster rash, alleviation of acute pain associated with shingles, and prevention of PHN.
Valacyclovir is very efficacious treatment for shingles. Valacyclovir helps to prevent the formation of new lesions, decreases the severity and duration of pain, and promote healing and crusting of lesions7. Also, it may shorten the duration of postherpetic neuralgia, particularly in people older than 50 years of age. Antiviral therapy for herpes zoster is most effective when initiated within 48-72 hours of rash onset.
Valacyclovir is also used to treat herpes zoster ophthalmicus6, the reactivation of a Varicella-zoster virus involving the ophthalmic nerve.
1 g three times daily for 7 to 10 days. Valacyclovir should be initiated within 72 hours of rash onset. However, it may be reasonable to begin antiviral therapy even after 72 hours, particularly if new vesicles are forming, or if a patient has a risk of complications.
Valacyclovir may be taken without regard to meals. In patients with reduced renal function, reduction in dosage is recommended.
Both antiviral medications valacyclovir and acyclovir are exceptionally safe, effective, and FDA approved for the treatment of herpes zoster.
The principal potential benefits of valacyclovir relative to acyclovir are improved oral bioavailability, and consequent higher blood levels, and a more convenient dosing schedule. Valacyclovir has oral bioavailability of 65%, whereas acyclovir has a poor oral bioavailability of 10%-20%.
In the treatment of shingles valacyclovir is more effective than acyclovir (its parent compound) in accelerating cutaneous healing, decreasing the frequency of persistent pain7, and in speeding the resolution of zoster-associated pain1, 3.
Both famciclovir and valacyclovir accelerate the resolution of zoster-associated pain and have convenient dosing schedule. Famciclovir is more expensive than valacyclovir.
One clinical study found that famciclovir was superior to valacyclovir in the relief of acute pain of herpes zoster2.
Mechanism of action
Valacyclovir prevents the growth and multiplication of the herpes virus.
Valacyclovir is selectively phosphorylated only within virus-infected cells by viral thymidine kinase (TK). Further phosphorylation by cellular enzymes leads to the production of acyclovir triphosphate, which competes with the natural nucleotide, dGTP, resulting in the selective inhibition of viral DNA polymerase. Incorporation of the analogue triphosphate into the growing DNA chain prevents continued extension of the DNA chain.