Absorption of topically applied hydrocortisone from the eye of the rhesus monkey

Blood samples were collected from anaesthetized monkeys during one h a) after topical application of an eyedrop of hydrocortisone acetate suspension, b) after topical application of a drop of the vehicle alone, and c) after no application at all. Radioimmunoassay (RIA) showed a rapid and similar increase of hydrocortisone plasma levels in all 3 kinds of experiments. RIA revealed that in monkeys the anaesthetic procedure alone was sufficient to cause a considerable increase of endogenous hydrocortisone levels overshadowing any systemic absorption of topical hydrocortisone. Using tritiated hydrocortisone instead a rapid increase of systemic absorption after topical application was found. A plasma concentration of 1% of the dose was found one min after topical instillation increasing to a maximum of 6-7% at 30 min. The half time of the show phase of elimination was about 19 h.