Three bellwether trials against drug manufacturer Merck & Co. are scheduled to take place this year. Opening statements for two consolidated Fosamax lawsuits are expected to begin today in the New Jersey state court.

Two women, Jo Ann Sessner and Ameila Flores, claim they developed osteonecrosis of the jaw (ONJ) after taking Fosamax. Osteonecrosis is a painful condition which causes the jaw bone to decay requiring surgery to remove portions of it.

Merck maintains that Fosamax did not cause Sessner and Flores to suffer jaw injuries. According to a statement released by the company’s legal counsel, “Unfortunately, both plaintiffs had medical problems that cause people to develop jaw problems regardless of whether they were taking Fosamax.”

Fosamax was introduced by Merck and approved by the Food and Drug Administration in October 1995 for the treatment of osteoporosis, a chronic condition which causes bones to become brittle and weak leading to possible breakage. It is included in a class of bone strengthening medications known as bisphosphonates. Prior to the release of a generic, Fosamax generated more than $3 billion in 2010.

An increased number of reported problems associated with bisphosphonate drugs such as Fosamax, Boniva®, and Reclast® caused the Food and Drug Administration to issue a bisphosphonate warning and later require manufacturers to update warning labels.

Currently Merck faces more than 1,000 Fosamax side effects lawsuits filed by women who have taken Fosamax for the treatment of osteoporosis. The lawsuits allege that Fosamax causes adverse side effects such as osteonecrosis of the jaw and atypical femur fracture injuries when taken for long periods of time, usually 12 months or more.

All femur fracture lawsuits have been consolidated in the U.S. District Court for the District of New Jersey while jaw decay lawsuits have been consolidated in the U.S. District Court for the Southern District of New York.