Anakinra (Kineret) is the first antirheumatic agent that acts by blocking the action of IL-1. This drug was re-cently approved for the treatment of moderately to se-verely active rheumatoid arthritis in adults who have not responded to therapy with one or more DMARDs. Anakinra may be used alone or in combination with DMARDs other than the TNF antagonists. Clinical trials have shown anakinra to be more effective than placebo, either alone or in conjunction with methotrexate.
Anakinra is a nonglycosylated form of the human IL-1 receptor antagonist (IL-1ra). It is produced in a recom-binant Escherichia coli expression system and has an additional methionine residue at its amino terminus. In rheumatoid arthritis patients, the amount of naturally occurring IL-1ra in the synovial fluid is not sufficient to counteract the high levels of locally produced IL-1. Anakinra acts as a competitive antagonist of the type 1 IL-1 receptor and decreases the pain and inflammation produced by IL-1. It is administered as a daily subcuta-neous injection.
The most common adverse reactions to anakinra are redness, bruising, pain, and inflammation at the injec-tion site. Neutropenia may occur, and the risk of serious infection is somewhat elevated, particularly in asth-matic patients. Antibodies to anakinra can develop with long-term therapy, but no correlation between antibody development and clinical response or adverse effects has been observed.
No drug interaction studies have been conducted in hu-mans. Animal studies indicate no change in the clear-ance or toxicity of either methotrexate or anakinra when the two agents are administered together. Con-comitant administration of a TNF blocker appears to increase the risk of serious infection. The response to vaccines may be diminished in patients taking anakinra.