Interferon: pharmacokinetics and toxicity.

Interferons disappear rapidly from the serum of animals and man, and the kidney may be the major site of interferon destruction. The relevance of serum levels of interferons to their therapeutic activity has not been clearly established, particularly as the stimulation of host defence mechanisms by interferons may be important. Relatively low serum levels of antiviral activity are seen after intramuscular injections of fibroblast interferon compared with those after the same dose of leucocyte interferon. Injections of very pure leucocyte and lymphoblastoid interferons from several sources cause fever, headaches, malaise and myalgia associated with a corticosteroid response and probably with inflammatory prostaglandin synthesis. These reactions become less with repeated dosing but very large doses of lymphoblastoid interferon have been shown to cause liver damage and serious metabolic disturbances. Treatment with moderate doses of exogenous interferons may occasionally be associated with the development of neutralizing antibodies.