Optimal schedules for use of interferon in the corneas of rabbits with herpes simplex keratitis

The 50% infectious dose of a preparation of herpes simplex virus was measured in eyes of rabbits by a multiple corneal inoculation method. One hour after inoculation of virus, one eye was treated with drops of human leukocyte interferon, and the other was treated with saline or with a different dose of interferon. Results from groups of three to four rabbits were combined for analysis. Treatment reduced the 50% infectious dose of virus in proportion to the concentration of interferon applied (within the range of 6.5 X 10(4)-1.3 X 10(6) units/ml) and not according to the total number of units instilled. Different treatment schedules were tried. Two applications of interferon each day were as effective as eight applications at intervals of 15 min or 1 hr. One application produced near-maximal antiviral effects for 18-24 hr. Thus, in human herpetic keratitis, a single daily application of the most concentrated available preparation of human interferon might be the most efficient schedule of treatment.