Valtrex Launched In Its First Markets

Wellcome has launched its new-generation antiviral drug, Valtrex (valaciclovir), onto the UK and Irish markets, just seven months after the applications for approval were submitted. This is the first launch of the new agent, which is a prodrug of aciclovir (Wellcome's best-selling Zovirax) and offers improved bioavailability and dosing, as well as increased efficacy in its first indication, Herpes zoster or shingles.

Valtrex is approved for the treatment of shingles at a recommended dose of 1,000mg three times daily for seven days. The compound is the valine ester of aciclovir and is converted into the active antiviral and valine in the body. Once inside the infected cell, aciclovir is activated by a viral enzyme (thymidine kinase) and then phosphorylated further by host enzymes to become the triphosphate form. In addition, it prevents further elongation of the viral DNA strand by a process known as obligate chain termination.

This dual mode of action is the key to aciclovir's (and valaciclovir's) potency and safety, said Graham Darby, senior molecular scientist at Wellcome's research facilities in Beckenham, UK. He believes that aciclovir remains the only active antiviral with both of these characteristics, and that this is the reason behind the drug's impressive safety profile. For example, SmithKline Beecham's recently introduced Famvir (famciclovir) does not have both these properties, but whether this will make any difference clinically in the tolerability of the drugs remains to be established. Certainly, there is no evidence to suggest a lower degree of tolerability with famciclovir from trials published to date.