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Valtrex

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.

Valacyclovir efficacy for Shingles

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.

Valacyclovir dosage for Shingles

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.

Valacyclovir vs Acyclovir (Zovirax) for Herpes Zoster

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.

Valacyclovir vs Famcyclovir (Famvir) for Herpes Zoster

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.

Benefits

  • Reduces severity of pain 3
  • Reduces duration and risk of PHN8, 9
  • Convenient dosing regimen
  • Favorable balance of potential benefit versus risk

Drawbacks

  • Does not cure the viral infection
  • Risk of renal and nervous system problems
  • 1.000 mg caplets are quite large and may be difficult to swallow

Pharmacological characteristics

  • Absorption and Bioavailability: After oral administration, valacyclovir is rapidly absorbed from the GI tract and nearly completely converted to acyclovir and L-valine. Bioavailability is about 50-60%. Administration with food does not alter bioavailability.
  • Metabolism: Valacyclovir is converted to acyclovir and L-valine by first-pass intestinal and/or hepatic metabolism. Valacyclovir is not metabolized by cytochrome P450 enzymes.
  • Elimination half-life: Elimination half-life is about 2.5-3.3 hours.
  • Excretion: About 46% is recovered in urine. About 47% is recovered in feces.

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.

References

  • 1. Wu JJ, Brentjens MH, Torres G, Yeung-Yue K, Lee P, Tyring SK. Valacyclovir in the treatment of herpes simplex, shingles, and other viral infections. J Cutan Med Surg. 2003 Sep-Oct;7(5):372-81.
  • 2. Ono F, Yasumoto S, Furumura M, et al. Comparison between famciclovir and valacyclovir for acute pain in adult Japanese immunocompetent patients with herpes zoster. J Dermatol. 2012 Nov;39(11):902-8. PubMed
  • 3. Lin WR, Lin HH, Lee SS, Tsai HC, Huang CK, Wann SR, Chen YS, Chiang SC, Yen MY, Liu YC. Comparative study of the efficacy and safety of valaciclovir versus acyclovir in the treatment of herpes zoster. J Microbiol Immunol Infect. 2001 Jun;34(2):138-42. PubMed
  • 6. Colin J, Prisant O, Cochener B, Lescale O, Rolland B, Hoang-Xuan T. Comparison of the efficacy and safety of valaciclovir for the treatment of herpes zoster ophthalmicus. Ophthalmology. 2000 Aug;107(8):1507-11. PubMed
  • 7. Beutner KR, Friedman DJ, Forszpaniak C, Andersen PL, Wood MJ. Valaciclovir compared with acyclovir for improved therapy for herpes zoster in immunocompetent adults. Antimicrob Agents Chemother. 1995 Jul;39(7):1546-53. PubMed
  • 8. Beutner KR. Antivirals in the treatment of pain. J Geriatr Dermatol 6: 23A-28A (1994).
  • 9. Lapolla W, Digiorgio C, Haitz K, Magel G, Mendoza N, Grady J, Lu W, Tyring S. Incidence of postherpetic neuralgia after combination treatment with gabapentin and valacyclovir in patients with acute herpes zoster: open-label study. Arch Dermatol. 2011 Aug;147(8):901-7. PubMed

By HealthyStock Research Group, October 2009
Medical resources reviewed: August 2018

Brief facts

Valacyclovir

  • Generic name: Valacyclovir hydrochloride
  • Trade names:Valtrex®
  • Pharmacologic category: Guanosine nucleoside analogue, Antiviral agent
  • FDA approved: December 15, 1995
  • Pregnancy risk factor: B
  • Patent Expiration Date: June 2009

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