Zovirax for canker sores? Is that a thing?

[Larry Mudd]

My wife asked her doctor for something for canker sores which have been annoying her lately, and when I picked up her prescription, it was Zovirax - in pill and cream form.

My initial reaction is that her doctor simply misunderstood her. On the other hand, I did find one website (belonging to a DDS in Nebraska) that says:

Canker Sore Updates

Valacyclovir (Valtrex) has just been approved for one day treatment of cancer sores. It shortens outbreaks of these painful sores by about one day.-acyclovir pills (Zovirax) and penciclovir cream (Denavir) and docosanol (Abreva) need to be used for four days or more and the creams must be applied throughout the day.

At $26.00 per treatment (two 2gram doses) is costs significantly less than Zovirax which runs about $71 per course or ($53 for generic). The creams are about $23 for a course of penciclovir and $14 for docosanol.

If you have recurrent sores, ask your doctor to prescribe Valacyclovir or other treatments you can keep on hand to use at the START of an outbreak. Or ask about taking acyclovir regularly, which can reduce the number of episodes by more than 80%.
Consumer Reports on Health pg 7 August 2003

I am still not sure about this, partly because a page that misspells "canker sores" as "cancer sores" doesn't inpire confidence, and partly because I'd think that after ten years there would be online reference to this use. On the other hand, this is hard to search for, because the search results are polluted by an inordinate number of dodgy online drug peddlars that have no actual content.

What's the straight dope on this? Legit use or vaguely embarrassing mistake?