Measuring the concentration of Humira (adalimumab) in the blood of patients with psoriatic arthritis being treated with the drug—something that’s not currently part of routine medical care—could lead to better clinical outcomes, according to a study published in August in the Annals of Rheumatic Disease.
Over a year, Dutch researchers periodically evaluated 103 psoriatic arthritis patients being treated with Humira to measure both their disease activity and their blood serum concentrations of the drug. This allowed the investigators to pinpoint the ideal blood concentration range for Humira, which they determined is 5 to 8 mg/L, said rheumatologist and study lead author Dr. Erik Vogelzang.
Concentrations above this range produced no additional benefits, while levels below it resulted in a less-than-optimal response.
A third of people in the study had blood serum concentrations below 5 milligrams per liter (mg/L), and more than half of these individuals developed antibodies to Humira. People with these antibodies, proteins that act specifically against Humira and lower concentrations of the drug in the blood, had more swollen and tender joints and a poorer clinical outcome overall than people without the antibodies.
In contrast, about half the patients had blood serum concentrations above 8 mg/L. “Based on the concentration effect curve, we believe patients with high adalimumab levels might still respond well on a lower dose,” Vogelzang said.
The researchers also found that the patients who were being treated with both Humira and methotrexate, a systemic drug used to treat inflammatory conditions, had higher concentrations of the biologic in their blood and were much less likely to develop antibodies to Humira.
Vogelzang said that, while there is an ongoing debate among experts about how well methotrexate works for the treatment of psoriatic arthritis, this research suggests that giving patients the drug at the same time as Humira can enhance patient outcomes.
Earlier research in patients with psoriasis who were using Humira also identified the development of anti-drug antibodies as a problem; about half the patients in a small 2010 study developed antibodies to the biologic that curbed clinical response.
Humira is not the only biologic to which patients develop anti-drug antibodies, said Vogelzang. A similar effect has also been seen in patients with rheumatoid arthritis who are using Remicade (infliximab).
“Information on drug concentrations could lead to a more tailored, evidence-based therapy for patients that is potentially cost saving,” he said.
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