The makers of Absorbine Jr. do consider their "horse liniment" (Absorbine Veterinary Liniment) to be useful for humans. Here's the link to one of the their descriptions of the product:
http://www.absorbine.com/absorbinejr...s/liniment.htm
The National Institutes of Health offers a
Low Back Bain Fact Sheet that includes a section of treatments. It also mentions topical analgesics that have salicylates in them, which includes products like Absorbine Veterinary Liniment as well as Ben-Gay and its immitations put out by the drug stores. The last time I had sharp back pain, I treated it with a drug-store knockoff of extra-strength Ben-Gay.
Here's a host of links from the Federal Government's Medline Plus regarding back pain:
http://www.nlm.nih.gov/medlineplus/backpain.html