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.