Effects of interleukin 1 receptor antagonist alone and in combination with methotrexate in adjuvant arthritic rats

To determine the benefit of combination treatment with the interleukin 1 receptor antagonist (IL-1ra) and methotrexate (MTX) in adjuvant arthritic rats.

Rats with adjuvant arthritis were treated by continuous sc infusion with IL-1ra (5 mg/kg/h). Effects of IL-1ra treatment alone were compared to treatment with daily oral MTX (0.048, 0.06, or 0.075 mg/kg) or MTX in combination with IL-1ra. Efficacy was monitored by sequential caliper measurement of ankle joints, final paw weights, and histologic evaluation with particular emphasis on bone lesions.

Treatment with IL-1ra alone resulted in 6% inhibition of paw swelling assessed by final paw weight. Treatment with MTX (0.075 mg/kg PO) gave 47% inhibition and the combination resulted in an 84% decrease in swelling. Histologic evaluation of ankle joints revealed 53% inhibition of bone resorption with IL-1ra alone, 58% inhibition with MTX alone, and 97% inhibition in combination treated rats. Lower doses of MTX in combination with IL-1ra also provided additive benefit on arthritis variables.

Combination therapy with IL-1ra and MTX results in additive or synergistic benefit, with excellent inhibition of all arthritis variables. These data support clinical investigation of the use of combination therapy of IL-1ra and MTX in patients with rheumatoid arthritis.