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The FDA today approved a new low-dose formulation of for the treatment of osteoarthritis pain, manufacturer Iroko Pharmaceuticals announced.

This formulation consists of submicron particles that are about 20 times smaller than in the conventional drug, which provides a greater surface area and more rapid drug dissolution and absorption, according to the company.

Zorvolex is intended to be a safer alternative to conventional nonsteroidal anti-inflammatory drugs (NSAIDs), which have been associated with potentially serious adverse events such as myocardial infarction and stroke, particularly if used in high doses and for extended periods.

Its efficacy and safety were assessed in a phase III trial that included 305 adults age 40 and older with radiologically evident osteoarthritis of the hip or knee who routinely used NSAIDs or acetaminophen.

They were randomized to receive submicron diclofenac, 35 mg either twice or three times per day, or placebo for 3 months.

Patients in the thrice-daily group had decreases on Western Ontario and McMasters Universities (WOMAC) 100-mm osteoarthritis index pain subscale of 44.1 mm compared with 32.5 mm for the placebo group (P=0.0024), according to , and colleagues.

The twice-daily regimen was numerically, though not statistically, superior to placebo for pain relief, with a decrease of 35.9 mm (P=0.0795), the investigators reported online in Current Medical Research and Opinion.

The most common adverse events in the active treatment groups were diarrhea, nausea, constipation, and headache.

Safety of the drug also was tested in a yearlong open-label study that included 600 patients.

The submicron formulation was previously approved for the treatment of mild to moderate acute pain in adult patients.

"NSAIDs continue to be an integral part of the management of osteoarthritis, the most common type of arthritis, and their use is likely to increase as the U.S. population continues to age and the incidence of osteoarthritis rises," commented Roy Altman, MD, of the University of California Los Angeles.

The availability of the submicron formulation of diclofenac "is a welcome and meaningful advance," Altman said in a news release.

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