Many Primary immunodeficiency diseases are characterized by the inability of the immune system to produce antibodies to various microbes. Therefore, one method of treatment is to medically replace antibodies. These products do not help the immune system itself to produce antibodies.
Blood plasma is collected from thousands of healthy people who are free from infectious diseases. Then antibodies (IgG) are isolated and purified to be used for many therapeutic purposes, including antibody replacement in some cases of primary immunodeficiency.
Antibodies are periodically administered through subcutaneous injection (on a weekly, biweekly, or monthly basis) or intravenous injection (every 3-4 weeks). A Patient continues to take this replacement therapy for life unless the condition resolves or the immune dysfunction is corrected through stem cell transplantation or gene therapy based on the type of disease.
Intravenously administered antibodies may result in the following side effects: Mild fever, muscle pain, or headache. Very rarely severe allergic reaction occurs with skin rash, shortness of breath, and hypotension.
In addition, subcutaneously administered antibodies may result local injection site swelling and redness which improve over time.
In case of intravenously administered antibodies, the dose usually starts with 400-600 mg per each kilogram of patient's weight per month.
In case of subcutaneously administered antibodies, the dose is 100-175 mg per each kilogram of patient’s weight per week. The final dose is eventually the same as the intravenous form.
Dosages are to be then adjusted in accordance with patient's response and the level of antibodies in blood (trough target level of IgG is about 8-10 g/l).