Stereoselective disposition of ibuprofen enantiomers in the isolated perfused rat kidney

The renal clearance of ibuprofen enantiomer was studied separately in the isolated perfused rat kidney at initial perfusate concentrations of 10 micrograms/ml (n = 4) and 100 micrograms/ml (n = 4). Perfusate and urine samples were measured for R(-) and S(+)-ibuprofen using a stereospecific HPLC assay; urine samples were also analyzed after alkaline hydrolysis. Functional viability of the kidney was assured by determining the fractional excretion of glucose and glomerular filtration rate (GFR) at similar perfusion pressures. The clearance of ibuprofen was equivalent to the apparent formation clearance of conjugated enantiomer since unchanged ibuprofen could not be detected in the urine. At 10 and 100 micrograms/ml, the clearance (+/- SD) of R(-)-ibuprofen was 2.50 +/- 1.28 and 2.19 +/- 1.42 microliters/min, respectively. At 100 micrograms/ml, the clearance of S(+)-ibuprofen was 0.805 +/- 0.290 microliters/min. The protein binding of ibuprofen was found to be concentration dependent and favored the R(-)-enantiomer. The excretion ratio (clearance corrected for free fraction and GFR) of R(-)-ibuprofen was 0.398 +/- 0.209 and 0.295 +/- 0.209 for perfusate concentrations of 10 and 100 micrograms/ml, respectively. The excretion ratio of S(+)-ibuprofen was 0.0886 +/- 0.0335 for perfusate concentrations of 100 micrograms/ml. These results demonstrate that the sum of renal mechanisms involved for the clearance of R(-)- and S(+)-ibuprofen was net reabsorption. Ibuprofen was recovered in the urine solely as conjugated material and no evidence of R(-) to S(+) conversion was observed. In addition, the data suggest that R(-)-ibuprofen is cleared through the kidney faster than its S(+)-enantiomer.

Topical delivery of liposomally encapsulated interferon evaluated by in vitro diffusion studies

The topical delivery of several liposomal interferon formulations was evaluated by in vitro diffusion experiments in an effort to understand the effects of liposomal composition and method of preparation on the deposition of interferon into the stratum corneum and deeper strata of the skin. Application of liposomes prepared from lipids with a composition similar to that of the stratum corneum resulted in almost twice the amount of interferon being deposited in the deeper skin layers than did application of liposomes prepared from phospholipids. Topical application of "skin lipid" liposomes prepared by the dehydration-rehydration method was twice as effective as was topical application of liposomes prepared by the reverse-phase evaporation method with respect to their ability to deposit interferon into the skin strata where the basal cell layers reside. These results are consistent with the effects of liposomal composition and method of preparation on the ability of the formulation to reduce lesion scores in the cutaneous herpes simplex virus type 1 guinea pig model.