The interaction of the penetration enhancer DDAIP with a phospholipid model membrane.

Differential scanning calorimetry (DSC) was used to investigate the mechanism of action of a proprietary skin penetration enhancer, dodecyl-2-(N,N-dimethylamino)propionate (DDAIP) in dipalmitoylphosphatidylcholine (DPPC) liposomes. Furthermore, the effect of enhancer concentration on lipid thermotropic transitions was investigated. With increasing concentrations of DDAIP (from 5 to 50 mol%), the main transition peak shifted to lower temperatures and became more broad. The pretransition peak also shifted to lower temperatures with increasing concentrations of DDAIP and disappeared completely above an enhancer concentration of 20 mol%. Main transition and pretransition enthalpies of reaction decreased with increasing DDAIP concentration, indicating that enhancer treatment destabilized both rippled gel and liquid crystal phases within the bilayer. At and above a DDAIP concentration of 33.3 mol%, an additional transition was evident, indicating the presence of two phases of enhancer-lipid complex. Results suggest that DDAIP enhances drug transport by interacting with the polar region of the phospholipid bilayer and also by increasing the motional freedom of lipid hydrocarbon chains.

Enhanced skin permeation of sex hormones with novel topical spray vehicles.

The feasibility of using some novel topical spray vehicles for enhanced transdermal delivery of the sex hormones, testosterone (Tes), estradiol (E2), progesterone (Prog), and norethindrone acetate (NA) has been investigated. The new penetration enhancers, padimate O (PadO) and octyl salicylate (OSal) were used and compared with laurocapram (AZ) and oleic acid (OA). A finite dose (5 microL/cm2) of each vehicle was applied to either shed snake skin or swine skin in vitro, and the amount penetrated was measured with flow-through diffusion cells. Partitioning into swine skin was determined after an exposure time of 1 min. Rapid partitioning of Tes and PadO into swine skin occurred after 1 min with 70% and 60% of the applied dose, respectively, remaining in the skin after the unabsorbed dose was removed by rinsing with absolute ethanol. The cumulative amount at 24 h (Q24 h) of Tes penetrating across the snake skin was significantly enhanced (p < 0.05) up to 6-fold for OSal, 3-fold for OA and AZ, and 2-fold for PadO compared to control. Using PadO or AZ, the Q24 h ranged from three- to thirteen-fold over control (p < 0.05) for E2, Prog, and NA. Extrapolation of these data to predict what would happen in humans suggests that it should be possible to deliver clinically relevant amounts of sex hormones in this manner with once daily dosing.

Enhanced transdermal delivery of sex hormones in swine with a novel topical aerosol.

This study investigated the enhanced transdermal delivery of testosterone (Tes) and estradiol (E2) in swine in vivo with novel metered-dose topical aerosols containing the penetration enhancer padimate O (PadO) and predicted the dose deliverable in humans from the calculated drug flux across the skin. Weanling swine were catheterized and castrated under general anaesthesia and used as a conscious hypogonadal model. Tes and E2 (with and without PadO) were applied once, and venous blood samples were taken over 24 h. Tes and E2 plasma levels were determined by radioimmunoassay. After daily topical dosing of Tes for 6 days, the plasma Tes levels were determined and the transdermal flux was calculated by correcting the pseudo steady-state plasma concentration versus time profile with the clearance of an iv dose within the same swine. After a single application of the E2 aerosol over 30 cm2, or the Tes aerosol over 180 cm2, the mean AUC0-24 h when PadO was included in the spray was 14.1- and 2.0-fold greater than control, respectively (p < 0.03). After the sixth application of the Tes spray with PadO, the mean flux (+/-SE, n = 4) across swine skin in vivo was 2.12 +/- 0.35 microg/cm2.h, which gave a predicted flux in humans of 0.95 microg/cm2.h. From these data the expected plasma levels of Tes in hypogonadal men would compare well with the normal diurnal Tes profile in healthy men. These novel topical aerosols are capable of enhanced transdermal delivery of sex hormones in vivo, and they have the potential to deliver clinically relevant doses to humans.

Transdermal delivery of estradiol in postmenopausal women with a novel topical aerosol.

The objective of this study was to determine if a novel metered-dose topical aerosol (MDTA) formulation containing the new dermal penetration enhancer, padimate O, could enhance the transdermal delivery of estradiol to an extent that would result in clinically relevant plasma concentrations. The estradiol MDTA (with padimate O) was applied once daily at 0800 h to postmenopausal women for 9 days, and plasma estradiol and estrone was measured daily (24 h postapplication) by radioimmunoassay. The topical dose was administered as three 1 mg doses of estradiol, each applied as a single spray over 10 cm2 which were placed adjacent to each other on the subject's ventral forearm. None of the subjects tested showed any sign of skin irritation at the application site over the entire study period using the Draize irritation score. In four postmenopausal women (age 54-63 years, weight 67-93 kg) the mean estradiol level 24 h postapplication over the 9 day study period was 53 pg/mL. This result was significantly greater (p < 0.001) than the baseline value of 13 pg/mL. The mean estradiol/estrone ratio also rose significantly (p < 0.04) from a baseline value of 0.2 up to 0.8. We conclude that this novel MDTA formulation significantly enhances the transdermal delivery of estradiol to allow a clinically relevant dose of estradiol to be delivered in postmenopausal women with once daily dosing.

Self-association of nicotinamide in aqueous solution: mass transport, freezing-point depression, and partition coefficient studies.

The steady-state flux (SSF) of nicotinamide from an aqueous donor phase across a model Silastic membrane did not increase proportionally with increasing donor phase concentration. The suspected self-association of the drug in aqueous solution was evaluated by studying the concentration-dependent changes in (i) the molal osmotic coefficient of nicotinamide (freezing-point depression studies) and (ii) the partition coefficient between water and n-octanol. The freezing points of aqueous solutions of nicotinamide were measured and a plot of osmolality vs molality was nonlinear. The partition coefficient of nicotinamide, studied at 15, 25, and 32 degrees C, also decreased with increasing concentration of drug. Mathematical models describing dimerization and higher orders of association were applied to the data. The results indicated the involvement of higher orders of association and it was found that an isodesmic (step-association) model was an adequate description of the freezing-point depression and partition coefficient data. The association constant, K, ranged between 1.59 +/- 0.02 M-1 at the freezing point and 0.48 +/- 0.01 M-1 as estimated from the partition coefficient data at 32 degrees C. These models for the self-association of nicotinamide allowed estimation of the apparent concentration of "monomeric" nicotinamide in the donor phase solutions studied in the SSF experiments. When the SSF data were analyzed with regard to the concentration of monomeric nicotinamide in the donor phase, a relationship close to linearity was observed.

Characterization of biopolymers by pyrolysis gas chromatography and multidimensional analysis. Application to synthetic melanins.

A method for characterization of the melanin biopolymer has been developed and validated by the use of synthetic melanins derived from tyrosine, dopamine or hydroquinone. The technique involved pyrolysis gas-liquid chromatography with capillary columns. A back-flushing technique is described which improves pyrogram reproducibility such that closely related melanins can be distinguished with the aid of principal components analysis and non-metric multidimensional scaling.

The lysosomal permeability test modified for toxicity testing with cultured heart endothelioid cells.

A modified lysosomal fragility test is described which is suitable for use with cultured cells. The permeability (fragility) of the lysosomal membranes of the cells to the substrate beta-glycerophosphate is measured by assessing the degree of particulate lysosomal straining seen after exposing the cells to the Gomori acid phosphatase staining reaction under carefully controlled conditions. Monolayer cultures of endothelioid cells from the hearts of neonatal rats have been used in all experiments. The time-course of lysosomal straining for cells exposed to various treatments (normal saline, isotonic sucrose, 0.25 m sucrose, distilled water, acetate buffer pH 5.0, cold acetone, neutral formalin, acetic-ethanol, Triton X-100, hydrocortisone, choloroquine and vitamin A) was compared with that of control cells stained under identical conditions. Statistical differences in staining between the test and control cells were determined by the Wilcoxin Signed Rank Test and also by regression analysis following a transformation designed to allow for the saturation character of the reaction. The success of the modified technique depends upon meticulous methodology. It is capable of demonstrating both lysosomal membrane labilization and stabilation, second- and third-stage lysosomal activation, and apparent lysosomal enzyme loss or destruction in situ. The technique also allows the degree of reversible or first-stage lysosomal activation to be subdivided on an almost continous basis and is suitable for investigating the effects of drugs and other agents on the integrity of the lysosome in situ.