PG-116800 is a member of the hydroxyproline-based hydroxamic acid class of matrix metalloproteinase (MMP) inhibitors. PG-116800 did not modify matrix structure in osteoarthritic patients. Also, it had unexpected side effects on muscle and skeleton; it limited joint mobility, and caused arthralgia, hand oedema, palmar fibrosis, Dupuytren’s contracture and persistent tendon thickness or nodules. PG-116800 failed to reduce left ventricular remodeling or improve clinical outcomes after myocardial infarction.

Ruzadolane (previously known as UP 26-91) is a serotonin receptor antagonist that was developed as a non-narcotic, centrally acting analgesic agent for the treatment of anxiety disorder and pain. However, these studies were discontinued.