The Influence of Liquid Crystalline Phases on Drug Percutaneous Absorption. I. Development of a Vehicle

A phase diagram approach has been used to formulate topically applied vehicles containing liquid crystalline phases. The current paper describes the construction of a major portion of the polyoxyethylene(20)cetyl ether:dodecanol:water phase diagram. Known mixtures of the three components were equilibrated and centrifuged to separate the resultant conjugate phases. These were identified and analyzed quantitatively to determine phase boundaries in relevant portions of the phase diagram. Two isotropic liquid phases, several two- and three-phase regions, a solid surfactant phase, and at least three distinct liquid crystalline phases were identified. The determination of tie lines was undertaken in a two-phase region containing an aqueous isotropic micellar solution and a liquid crystalline gel. This information will be used to prepare a number of vehicles of known phase composition and concentration for a systematic evaluation of the effect of liquid crystalline phases on transdermal drug delivery.__________________________     

Qualitative differences in the visual retention test performance of older non-insulin dependent diabetic patients

To evaluate the qualitative and quantitative differences in the performance of older diabetic patients on Benton’s Visual Retention Test (BVRT), a cross sectional study of 46 non-insulin dependent diabetic men and 59 nondiabetic men over the age of 55 years was carried out. The recent memory was assessed with the Benton’s Visual Retention Test. Diabetic patients had a significantly higher error score (10.96 ± 4.07) compared to nondiabetic subjects (9.08 ± 4.45), F (1,103) = 4.923, p<0.029. Diabetic patients were more likely to make the following types of errors: omissions, distortions, size errors and left errors. Older diabetic patients appear to have mild impairment in recent memory compared to nondiabetic subjects. The qualitative pattern of the test results is suggestive of cerebrovascular etiology of the cognitive changes.     

The Influence of Liquid Crystalline Phases on Drug Percutaneous Absorption. II. Permeation Studies Through Excised Human Skin

The influence of liquid crystalline (LC) phases on the percutaneous absorption of a model compound (ploxicromil; PXC) was studied with the use of the phase diagram for the surfactant, oil, and water comprising the vehicles. Two separate sets of vehicles, representing two different tie lines lying in the Ll + LC phase region, were prepared in which the concentration of LC was varied over the range 0 to 100% along each tie line. In vitro permeation studies of PXC from these systems were conducted using excised human skin and the flux values determined as a function of the percentage LC present in the vehicles. In virtually all cases, the flux reached a peak at 5-10% LC and then decreased significantly as the fraction of LC present increased further. The pattern of behavior observed is discussed in terms of current theories describing membrane-controlled and vehicle-controlled diffusion, none of which adequately model the results obtained.