Bioavailability of gamma-globulin after subcutaneous infusions in patients with common variable immunodeficiency

Replacement therapy, using subcutaneous infusions of gamma-globulin, is being applied increasingly for antibody-deficient patients, as this form of treatment has been found to be related to a very low frequency of adverse systemic reactions. However, the uptake of IgG from subcutaneous tissue may be low, owing to degradation locally, especially for the IgG3 molecule. Therefore, the kinetics of IgG and IgG-subclass concentrations in the sera of 23 patients with common variable immunodeficiency was investigated during 18 months of subcutaneous infusions of gamma-globulin (100 mg/kg/week). Seventeen patients were previously treated with intramuscular injections or intravenous infusions. The mean serum IgG level increased twice in the previously treated patients and four times in the previously untreated patients. A steady state was reached after 6 months if the subcutaneous infusions were given weekly and after 1 week if the patients were given daily infusions for 5 consecutive days and, thereafter, weekly infusions. The fractional catabolic rate of IgG (4.1-5.9% per day) was found to be at the lower limit reported for normal controls, if 100% bioavailability of the infused IgG was assumed. The fractional contents of IgG subclasses in the patients' serum IgG resembled the physiological pattern, with the exception of IgG4, which was not present in the gamma-globulin preparations used. Significantly increased levels of IgG1 and -2 were seen in both previously treated and untreated patients during the treatment.