The preliminary analysis of a clinical trial for a potential successor to
Vioxx provided mixed results about the experimental drug's safety compared with a prescription pain reliever that has been on the market since 1988.
The experimental drug is Arcoxia, which Merck had been developing long before the
company removed Vioxx from the market in September 2004, citing safety concerns. Arcoxia, a chemical cousin to Vioxx, received conditional approval from the Food and Drug Administration in October 2004, but the agency wanted to see more clinical-trial data on safety and effectiveness.
Merck's study says the rate of blood clots leading to heart damage in Arcoxia patients was statistically similar to the clot rate for people taking the generic pain-reliever diclofenac. However, the study, which uses the acronym MEDAL, says the rate of people dropping out of the trial due to high blood pressure "was significantly higher for Arcoxia compared to diclofenac."
The study consisted of three clinical trials involving patients who have osteoarthritis or rheumatoid arthritis. Some received diclofenac, some received 60 milligrams of Arcoxia and others received 90 milligrams of Arcoxia.
Merck said patients taking the higher dose of Arcoxia had a "significantly higher" dropout rate from the clinical trials because of edema-related side effects vs. people who took diclofenac. Edema is the buildup of fluid in the body.
Additionally, patients taking the higher dose of Arcoxia had a higher rate of congestive heart failure compared with those taking diclofenac. Merck said diclofenac patients had a much higher quit rate because of gastrointestinal side effects and liver problems.
"After four years of conducting this arthritis study program in more than 34,000 patients, we are looking forward to sharing the full MEDAL program results in the future," said Dr. Peter S. Kim, president of Merck Research Laboratories, in a prepared statement. The company didn't provide details or a timetable for presenting the data at scientific meetings or in science journals.
Merck said the data is being "verified by an independent statistical center." Preliminary data has been sent to the FDA, its counterpart at the European Union and other countries' regulatory agencies. Arcoxia is available in 62 countries.
Like Vioxx, Arcoxia belongs to a class of drugs known as COX-2 inhibitors. The only COX-2 drug available in the U.S. is
In April 2005, Pfizer suspended sales of another COX-2 drug, Bextra, at the request of the FDA. Last September, the FDA
rejected Pfizer's application to sell another COX-2 drug called Dynastat. Next year, Novartis is expected to seek FDA approval for its COX-2 drug.
Merck continues to develop Arcoxia more than a year after the FDA ordered
tougher safety warnings for prescription and nonprescription pain relievers, alerting patients to potential cardiovascular risks.
The warnings cover COX-2 drugs such as Celebrex as well as medications like diclofenac, which belong to the class known as nonselective, nonsteroidal anti-inflammatory drugs. Diclofenac reached the U.S. market under the brand name Voltaren from
and is now generic. Merck says diclofenac is the most-prescribed pain reliever in the world.
The category of nonsteroidal drugs includes ibuprofen and naproxen, which are sold via prescription or over the counter.
Merck withdrew Vioxx, citing a company-sponsored clinical trial that showed patients who took it for more than 18 months were at greater cardiovascular risk than those getting a placebo.
Merck says the cardiovascular risk for taking Vioxx for less than 18 months is statistically similar to a placebo. Critics have disagreed, arguing that the drug can present a heightened risk even if it's taken for less than a year and a half.
Merck is defending at least 14,200 personal injury suits against Vioxx in the U.S.