Biologics are a recent addition to the clinician’s list of prescribable drugs for psoriatic arthritis.
They act by mimicing the effects of substances naturally made by the immune system of the patient. They are manufactured using genetic engineering, meaning that human genes that normally guide the production of these natural human immune proteins (i.e., an antibody to TNF) are used in artificial ways to produce large amounts of a biologic drug. These drugs are given to lessen inflammation by interfering with biologic substances that cause or worsen inflammation.
Biologic agents have been approved to treat moderate to severe psoriatic arthritis that has not responded to one or more of the traditional disease modifying antirheumatic drugs DMARDs. They are not generally considered as first-line treatments because of their expense and side effects, unless patients are unable to take methotrexate because of side effects or other conditions. Biologic agents may be used alone, but are often given in conjunction with other DMARDs to increase the benefit and limit potential side effects. When patients start biologic agents, they usually also remain on their current dose of non-steroidal anti-inflammatory NSAIDs and/or corticosteroids (i.e., prednisolone) medicines.
Currently available biologic agents act as inhibitors of the cytokines, IL-1 or TNF. Cytokines are messenger molecules made by many of the body's cells that act to excite other immune system cells. Interleukin-1 (IL-1) and tumour necrosis factor (TNF) are made in large amounts in rheumatoid arthritis and other forms of inflammation. TNF or IL-1 acts to increase inflammation, similar to the effect of adding petrol to a fire. Hence, these molecules amplify and worsen inflammation and joint damage. Biologic agents specifically attach to TNF or IL-1 and inhibit or inactivate them.
Biologic agents are given by injection and usually work quickly to relieve the symptoms and swelling associated with psoriatic arthritis. Although the studies show that most patients will improve within 4-6 weeks of treatment, most patients will notice some improvement after the first or second injection.
The most common side effects seen with all injectable medicines include skin reactions at the injection site. These occur in less than 30% of patients. These skin reactions may last for between 1 and 2 weeks. The most significant side effect of these medications is an increase the risk of all types of infections, including tuberculosis (TB). Before starting an anti-TNF medication a TB skin test is usually done. Treatment with these agents should be stopped while you have an active infection and are taking an antibiotic or if you have a high fever. People with significant congestive heart failure should not take the anti-TNF agents.
Current available biologic agents