IgG subclasses in epileptic patients treated with phenytoin.

IgG1, IgG2, IgG3 and IgG4 serum concentrations were determined in 49 phenytoin-treated epileptic patients and in 19 untreated epileptic controls, using subclass-specific monoclonal antibodies in an ELISA technique. The IgG3 and IgG4 concentrations were significantly reduced in patients with IgA deficiency (P less than 0.05, P less than 0.01 respectively). In contrast, IgG4 was elevated in the patients in whom phenytoin did not induce an IgA deficiency (P less than 0.05). IgG1 and IgG2 concentrations did not differ in phenytoin-treated and untreated epileptic patients. IgG1, IgG2, IgG3 and IgG4 did not change after withdrawal of phenytoin. IgG subclass concentrations were not significantly correlated with frequency of respiratory tract infections.