How Pennsaid Topical Solution Helps Knee Osteoarthritis

Pennsaid is a topical NSAID solution that received FDA approval on November 4, 2009, to treat pain and symptoms associated with knee osteoarthritis. The generic name for Pennsaid is diclofenac sodium. Pennsaid was developed by Nuvo Research Inc. This is a topical version of diclofenac, also available as a pill.

How Does Pennsaid Work?

All non-steroidal anti-inflammatory drugs (NSAIDs) work by a similar mechanism. They inhibit cyclooxygenase, an enzyme responsible for the production of prostaglandins, which are chemical messengers key to the inflammatory cascade. By inhibiting that enzyme, NSAIDs lead to decreased levels of prostaglandins and thus less inflammation. Unfortunately, prostaglandins are instrumental in other functions of the body, and thus NSAIDs have some adverse side effects. Notably, prostaglandins are key in the production of the mucous membrane of the stomach which is important in protecting the stomach lining from acid. NSAIDs, by decreasing prostaglandins, leading to impairment of this protective barrier and can lead to stomach irritation and ulcers.

The theory behind using topical NSAIDs is that a local application of the drug will lead to a decrease in inflammation, and associated decrease in pain at the site of application, but the drug will not reach high enough blood concentrations to lead to the systemic side effects such as stomach ulcers. In fact, studies have shown that with topical application of NSAIDs the systemic levels of the drug are only about 5% of what they are inside the tissues where the drug was applied. 

Adverse Effects Similar to Oral NSAIDs

The use of topical NSAIDs in the treatment of knee osteoarthritis offers potential significant gastrointestinal safety benefits for certain patients. The mechanism behind these benefits as described above. Localized treatment may be safer and more tolerable compared to oral NSAIDs.

The potential for adverse events such as ulcers, gastrointestinal bleeding, and cardiovascular risks still exist but are lower comparing to the pill form of these drugs.

The most common side effect associated with Pennsaid is mild dryness or irritation where it is applied.

Does It Work?

A review done by The Cochrane Collaboration looked at 61 studies that investigated whether topical NSAIDs work. In short, the answer is yes. When combining data from all the studies, the approximately 75% of people experienced significant relief of muscle/joint pain (significant relief defined as a decrease in pain by half) when using topical diclofenac, this is in contrast to approximately 50% of people that received placebo.