Total-cost analysis favors infliximab over etanercept for treatment of psoriatic arthritis

March 1, 2008

In a recent psoriatic arthritis study, infliximab was associated with lower total medical costs, including hospitalizations, physician visits and OTC drug purchases.

Key Points

Buenos Aires, Argentina - For patients with psoriatic arthritis (PsA), the use of Remicade (infliximab, Centocor) results in lower medical costs compared to using Enbrel (etanercept, Amgen/Wyeth), according to a recent study.

"The assumption people usually make is that if one uses biologics, medical costs are going to go up," says Mirza I. Rahman, M.D., M.P.H., senior director, health economics and clinical outcomes research in the medical affairs department of Centocor, Horsham, Pa., and a study co-author.

However, he says that in the study - which considered total medical costs, including costs of inpatient care, outpatient visits, physician visits, emergency room visits and laboratory services - use of infliximab was associated with lower costs than use of etanercept.

Additionally, patients spend more than $350 million on over-the-counter (OTC drugs) to treat psoriasis, including PsA, Dr. Rahman tells Dermatology Times.

The retrospective study analyzed claims data from the PharMetrics Patient-Centric database, a managed-care resource aggregating information from more than 40 million patients served by various insurers, he says.

"We looked at the data from January 2001 to January 2004, and at any point within that period when someone would have started on a biologic, we used that as the index biologic starting date," Dr. Rahman says. Researchers also incorporated PsA-related claims data from a period beginning six months before an actual biologic starting date, until 12 months after that index biologic starting date.

Methodologically, researchers considered all claims - except for adverse events (AE) costs and pharmacy costs - that occurred on the same day as a claim for infliximab (or etanercept) in their total cost analysis.

This method had the potential to overstate true medical costs, but researchers preferred this approach to potentially understating these costs.

"For example, if a patient went to see their doctor and got an infliximab infusion, but unfortunately developed an unrelated second medical problem on that day, we would have no way of knowing if the second cost was or was not related to infliximab," Dr. Rahman says. "But usually, we factor in costs from the claim date so as not to underestimate the true medical costs."

Additionally, if a patient had an adverse drug reaction and required hospitalization, "Those costs would turn up in the inpatient charges and are thus captured in our medical costs, even if we cannot separate them individually," he says.

Calculated costs

Researchers calculated total costs in two ways: once based on total claims during the enrollment period, and a second time excluding patients with total costs more than two standard deviations from the mean to adjust for outliers. The second analysis encompassed 95 percent of the sample population, Dr. Rahman says.

"Then we developed a multivariate model that adjusts for the covariates. We looked at age, gender, Charlson Comorbidity Index (CCI) score and pre-biologic healthcare costs," he says.

The CCI helps account for the fact that a person with PsA and other conditions such as diabetes, hypertension and rheumatoid arthritis, for instance, likely will have more severe PsA than a patient who has only PsA, Dr. Rahman says.

Ultimately, researchers focused on a total of 360 patients, 308 of whom took etanercept or etanercept plus methotrexate and 52 who took infliximab or infliximab plus methotrexate. Those in the latter group were nearly three years older (P = 0.046), which was the only variable that reached statistical significance, Dr. Rahman says.

Patients treated with infliximab also were slightly more likely to be treated by rheumatologists, and to have higher CCI scores.

Overall, etanercept-treated patients had more medical visits and associated total costs than those treated with infliximab, he says.

In particular, etanercept-treated patients had a mean of 10.54 medical visits versus 8.65 in the infliximab group.

Mean total medical costs per patient per month were nearly $670 in the etanercept group versus slightly more than $402 in the infliximab group, while total medical visit costs were $499 and $247, respectively.

Dr. Rahman says when treating a patient with a biologic drug, along with efficacy, safety and patient preferences, one also should consider medical costs and resource utilization.

"For managed care organizations that may have to provide healthcare to millions of people," he says, "these incremental costs, while they may be small on an individual basis, may become quite large in aggregate."

Disclosure: This study was supported by Centocor.

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