# E-DRUG: Acyclovir or valazyclovir? **URL:** \ **Category:** e-drug\ **Created:** [November 12, 1998, 5:58am UTC](https://talk.edrugplus.org/t/e-drug-acyclovir-or-valazyclovir/3813 "1998-11-12T05:58:10Z")\ **Posts on this page:** 1\ **Page:** 1
**Author:** ![joel.lexchin](https://avatars.discourse-cdn.com/v4/letter/j/e9c0ed/32.png) [@joel.lexchin](https://talk.edrugplus.org/u/joel.lexchin)\ **Post date:** [November 12, 1998, 5:58am UTC](https://talk.edrugplus.org/t/e-drug-acyclovir-or-valazyclovir/3813/1 "1998-11-12T05:58:10Z")
E-DRUG: Acyclovir or valazyclovir? (4) -------------------------------------- Here is a reprint of an article on this topic that appeared in the Therapeutic Letter which is a product of the Therapeutic Initiative in British Columbia. Basically, there is no evidence that any one of the three drugs (acyclovir, famciclovir or valacyclovir) is superior. ------------------------ Famciclovir (Famvirr) and Valacyclovir (Valtrexr) Both are new antiherpesviral prodrugs (in the same class as acyclovir). Indication: Acute herpes zoster in the immunocompetent host. (Their role in genital herpes will be discussed in a future Therapeutics Letter). Mechanism of Action: Reduce viral replication by inhibiting viral DNA polymerase. Pharmacokinetics: Valacyclovir is a prodrug of, and metabolized to acyclovir; the oral bioavailability of acyclovir from valacyclovir is 54% as compared to 15-30% for acyclovir. Famciclovir is a prodrug for the active metabolite penciclovir; the mean oral bioavailability of penciclovir from famciclovir is 77%. Penciclovir plus acyclovir are primarily eliminated unchanged by the kidneys and have mean half-lives of 2.5 hours. Evidence of efficacy: If given within 72 hours of the first herpes zoster lesion, famciclovir(1) and valacyclovir(2) (like acyclovir(3)) provide modest decreases in the time to full crusting (e.g. median 5.5 days for famciclovir, 7 days for placebo(1)), healing and cessation of pain . The benefit is greatest in patients with the most severe infections (many lesions and severe pain)(1),(3),(4). At present the evidence is inconclusive as to whether any antiviral or other therapy has an effect on the overall clinical impact of post-herpetic neuralgia.(4) The new prodrugs have not been studied in children or immunocompromised hosts. Major adverse effects: These drugs, like acyclovir, produce a low incidence (similar to placebo) of minor adverse effects, including diarrhea, nausea and headache. Dose and Cost: Acute herpes zoster: famciclovir, 500 mg TID for 7 days ($155.61), valacyclovir, 1 g TID for 7 days ($126.84), acyclovir, 800 mg 5 times daily for 7 days ($138.60). Longer durations of therapy are not more effective; shorter courses have not been tested. Conclusions: Anti-viral drugs have a modest beneficial effect if given early (rash \<72 hr) to immunocompetent patients (\>50 yr) with moderate to severe rash or pain associated with acute herpes zoster (shingles). References: 1.Tyring S, Barbarash RA, Nahlik JE, et al. Famciclovir for the treatment of acute herpes zoster: effects on acute disease and postherpetic neuralgia. A randomized, double-blind, placebo-controlled trial. Collaborative Famciclovir Herpes Zoster Study Group. Annals of Internal Medicine. 1995 July 15; 123(2):89-96. 2.Beutner KR, Friedman DJ,Forszpaniak C, et al. Valaciclovir compared with acyclovir for improved therapy for herpes zoster in immunocompetent adults. Antimicrob Agents Chemother. 1996;39:1546-53. 3.Whitley RJ, Weiss H, Gnann JW, et al. Acyclovir with and without prednisone for the treatment of Herpes Zoster. A placebo-controlled trial. Ann Intern Med. 1996; 125:376-383. 4.Kost RG, Straus SE. Postherpetic neuralgia - pathogenesis, treatment, and prevention. NEJM. 1996 July 4; 335:32-42. ----------------------- Joel Lexchin Joel Lexchin MD 121 Walmer Rd. Toronto, Ontario CANADA M5R 2X8 Phone: (416)-964-7186 Fax: (416)-923-9515 e mail: joel.lexchin@utoronto.ca -- Send mail for the `E-Drug' conference to `e-drug@usa.healthnet.org'. Mail administrative requests to `majordomo@usa.healthnet.org'. For additional assistance, send mail to: `owner-e-drug@usa.healthnet.org'.