The 'magic mouthwash' I was a prescribed was a 'swish and swallow' teaspoon dose of a prescription 2% Lidocaine Hydrochloride Oral Topical Solution containing 20mg or Lidocaine HCL per mL.

The manufacture was Hi-Tech Pharmacal (NDC 0383-774-04).
http://www.hitechpharm.com/product

It works OK, but a noted side-effect was it seemed to numb the whole throat and made swallowing a lot less painful but a bit more difficult for a half hour or so.

Don
TXN2bM0 Stage IVa SCC-Occult Primary
FNA 6/6/08-SCC in node<2cm
PET/CT 6/19/08-SCC in 2nd node<1cm
HiRes CT 6/21/08
Exploratory,Tonsillectomy(benign),Right SND 6/23/08
PEG 7/3/08-11/6/08
35 TomoTherapy 7/16/08-9/04/08 No Chemo
Clear PET/CT 11/15/08, 5/15/09, 5/28/10, 7/8/11