Pharmacokinetics of human leukocyte interferon

Most of the human leukocyte interferon or rabbit serum interferon administered intravenously to rabbits was detectabble in their plasma 1 min after injection. An increase in the dose did not affect the early clearance of human interferon but did prolong its persistence in the serum. Repeated intramuscular injections had no effect on the kinetics of circulating interferon. The purity of the preparation influenced the rate at which interferon entered the blood after intramuscular or subcutaneous injection but did not affect clearance from the blood after intravenous injection. The circulating interferons obtained after intravenous or intramuscular administration cleared at similar rates. During the first 1-2 hr after intravenous or intramuscular injection into rats, the interferon levels were lower in lymph than in serum; after 2 hr lymph and serum samples contained similar amounts of interferon.