May 2 (Reuters) - Drugmaker Regeneron Pharmaceuticals Inc said on Monday its experimental drug to treat moderate-to-severe osteoarthritis pain was successful in a late-stage study.

The drug, fasinumab, was tested on 421 patients with a history of inadequate pain relief or intolerance to current painkillers.

After 16 weeks, patients given fasinumab reported less pain, as measured on a physician-grade scale, than those given a placebo, Regeneron said in a statement.

Current treatments for pain management include non-steroidal anti-inflammatory drugs, anti-seizure agents, and opiates. However, these drugs cause multiple side-effects and often prove to be toxic with long-term use.

Fasinumab binds to nerve growth factor (NGF) proteins and block their activity, reducing pain.

A number of companies, including Pfizer Inc and Eli Lilly & Co, are developing drugs that target NGFs.

The U.S. Food and Drug Administration placed fasinumab and other experimental agents targeting NGF on partial clinical hold in December 2012 after reports that animals treated with these drugs had nerve damage.

Fasinumab is no longer on clinical hold, according to Regeneron's website.

(Reporting by Amrutha Penumudi in Bengaluru; Editing by Savio D'Souza)