I just recently attended a continuing Ed course taught by a very knowledgable, compounding pharmacist. Subjects included new meds for treatment of herpes simplex, as well as other ailments we see in dentistry. He stated the new products are as effective, if not more so, on Herpes Simplex as the systemic Valtrex....if you can find them.
HsPLEX is sold as 25 over-the-counter capsules for $27.95 US dollars, but wholesale cost is about $16 so you might find it for less. It contains B-complex, L-lysine, Vit C, Magnisium, and Zinc Sulfate...(but remember Zinc exacerbates the effectiveness of Xeloda, so if you're on Xeloda, talk to your Onc first before taking it). Follow the directions on the bottle.
But the better option, if you can catch it when you first notice symptoms, is the "new" RX, A-VIR LIP BALM. It's obviously topical and won't be subjecting your body systemically to the comparatively huge anti-viral load of Valtrex. It contains Acyclovir and L-lysine. Apply it 5 times a day as soon as you start feeling symptoms until symptoms disappear (a few days). The tube will last 1-2 years. Sorry, didn't catch the cost.
Again, it goes without saying, if you're on chemo run everything by your Onc first, That was the same advise the pharmacist gave, although he went on to say the minute amounts of anti-viral load you would be applying in the topical lip balm would seem to be the safest, most effective route, chemo or not.