The relationship between hydrocortisone acetate distribution and efficacy in inflamed eyes: continuous vs intermittent delivery

Hydrocortisone acetate was administered to rabbit eyes intermittently in 250mug doses (given twice daily or once hourly) or continuously at 10mug/hr from an experimental ocular therapeutic system. Tissue drug distribution was measured over a 1 to 4 day period in experimental conjunctivitis. Anti-inflammatory efficacy was evaluated over a 4 day period in the same model. Statistically significant improvement in inflammation was observed 48 hours after initiation of continuous delivery treatment and after 4 days of the twice daily eyedrop regimen. Drug uptake by ocular tissues correlated with drug efficacy. Continuous delivery at 10mug/hr produced conjunctival steriod concentrations exceeding 1mug/g during 8 through 24 hours of treatment, and average levels of 1mug/g from days 2 through 4. Conjunctival steroid concentations generally did not exceed 1mug/g in eyedrop treated eyes until the fourth treatment day, when their clinical improvement matched that observed in the continuously treated eyes.

Intermittent vs continuous steroid administration. Efficacy in experimental conjunctivitis

The development of techniques for the continuous administration of drugs to the eye raises the question of whether a conjunctivitis can be controlled by continuous low rates of steroid release, or whether large, intermittent doses of steroid, as provided by eyedrops, are necessary. Efficacy of the two modes of drug administration was evaluated in a conjunctivitis model produced in immunized rabbits by daily topical ocular challenge with antigen. The acetates of hydrocortisone and prednisolone were released from a drug delivery system inserted in the cul-de-sac of the eye or were provided in eyedrops. The model was sufficiently sensitive to differentiate between the effectiveness of hydrocortisone and prednisolone. The continuous delivery of either steroid from the drug delivery system was as efficacious, or more so, than the corresponding steroid dose given as eyedrops.

In situ and pilot organ perfusion techniques for the study of metabolic dynamics

Two techniques for organ perfusion with blood are described which provide a basis for exploring metabolic or endocrine dynamics. The technique of in situ perfusion with autogenous arterial blood is suitable for glands or small organs which receive a small fraction of the animal's cardiac output; thus, test stimulatory or inhibitory substances can be added to the perfusing blood and undergo sufficient dilution in systemic blood after passage through the perfused organ so that recirculation does not compromise experimental control over test substance concentration in the perfusate. Experimental studies with the in situ perfused adrenal are described. The second technique, termed the pilot organ method, is suitable for organs which receive a large fraction of the cardiac output, such as the liver. Vascular connections are made between the circulation of an intact, anaesthetized large (> 30 kg) dog and the liver of a small (< 3 kg) dog. The small dog's liver (pilot liver) is excised and floated in a bath of canine ascites, and its venous effluent is continuously returned to the large dog. Test substances are infused into either the hepatic artery or portal vein of the pilot liver, but the small size of the pilot liver and its blood flow in relation to the large dog minimize recirculation effects. A number of functional parameters of the pilot liver are described.