Circulating interferon in rabbits and monkeys after administration of human gamma interferon by different routes

Rabbits and rhesus monkeys were injected with 3 X 10(5) units of human gamma interferon (IFN) prepared in human leukocyte suspensions. Circulating IFN was detected up to 4 h after intravenous administration. Intramuscular injection maintained a relatively stable serum IFN level of about 50 units/ml for 7 to 9 h. The results in both species were similar. Little or no circulating IFN was detected after subcutaneous injection of 3 X 10(5) units, but 1.5 X 10(6) units maintained about 50 units per ml of serum for 30 h. Pharmacokinetically, human gamma IFN resembled human alpha interferons rather than human beta IFN.